Stratospheric sulfur aerosols

Stratospheric sulfur aerosols are tiny sulfur-rich particles of solid or liquid, or a mixture of the two, which exist in the stratosphere region of the Earth's atmosphere. When present, after a strong volcanic eruption such as Mount Pinatubo, they produce a cooling effect for a few years before the particles fall out, by reflecting sunlight, and by modifying clouds as they fall out of the stratosphere.

An aerosol is a suspension of fine solid particles or liquid droplets in a gas. The sulfate particles in the atmosphere are about 0.1 to 1.0 micrometer (a millionth of a meter) in diameter.

Sulfur aerosols are common in the troposphere as a result of pollution with sulfur dioxide from burning coal, and from natural processes. Volcanos are the major source of particles in the stratosphere as the force of the volcanic eruption propels sulfur-containing gases into the stratosphere.

Creating stratospheric sulfur aerosols deliberately is a proposed geoengineering technique which offers a possible solution to some of the problems caused by global warming. However, this will not be without side effects and it has been suggested that the cure may be worse than the disease.

Origins



Natural sulfur aerosols are formed in vast quantities from the SO2 ejected by volcanoes, which may be injected directly into the stratosphere during very large (Volcanic Explosivity Index (VEI) of 4 or greater) eruptions. A comprehensive analysis, dealing largely with tropospheric sulfates in the atmosphere, is provided by Bates et al.

The IPCC AR4 says explosive volcanic events are episodic, but the stratospheric aerosols resulting from them yield substantial transitory perturbations to the radiative energy balance of the planet, with both shortwave and longwave effects sensitive to the microphysical characteristics of the aerosols. There have been no explosive and climatically significant volcanic events since Mt. Pinatubo. Consequently, stratospheric aerosol concentrations are now at the lowest concentrations since the satellite era and global coverage began in about 1980.

During periods lacking volcanic activity (and thus direct injection of SO2 into the stratosphere), oxidation of COS (carbonyl sulfide) dominates the production of stratospheric sulfate aerosol.

Chemistry

The chemistry of stratospheric sulfur aerosols varies significantly according to their source. Volcanic emissions vary significantly in composition, and have complex chemistry due to the presence of ash particulates and a wide variety of other elements in the plume.

The chemical reactions affecting both the formation and elimination of sulfur aerosols are not fully understood. It is difficult to estimate accurately, for example, whether the presence of ash and water vapour is important for aerosol formation from volcanic products, and whether high or low atmospheric concentrations of precursor chemicals (such as SO2 and H2S) are optimal for aerosol formation. This uncertainty makes it difficult to determine a viable approach for geoengineering uses of sulfur aerosol formation.

Scientific study



Understanding of these aerosols comes in large part from the study of volcanic eruptions,notably Mount Pinatubo in the Philippines, which erupted in 1991 when scientific techniques were sufficiently far advanced to study the effects carefully.

The formation of the aerosols and their effects on the atmosphere can also be studied in the lab. Samples of actual particles can be recovered from the stratosphere using balloons or aircraft.

Computer models can be used to understand the behaviour of aerosol particles, and are particularly useful in modelling their effect on global climate.

Biological experiments in the lab, and field/ocean measurements can establish the formation mechanisms of biologically-derived volatile sulfurous gases.

Effects

Effect on climate

It has been established that emission of precursor gases for sulfur aerosols is the principle mechanism by which volcanoes cause episodic global cooling.

The Intergovernmental Panel on Climate Change AR4 regards stratospheric sulfate aerosols as having a low level of scientific understanding.

The aerosol particles form a whitish haze in the sky. This creates a global dimming effect, where less of the sun's radiation is able to reach the surface of the Earth. This leads to a global cooling effect. In essence, they act as the reverse of a greenhouse gas, which tends to allow visible light from the sun through, whilst blocking infra-red emitted from the Earth's surface and its atmosphere. The particles also radiate infra red energy directly, as they lose heat into space.

Effects on light transmission through the atmosphere



All aerosols both absorb and scatter solar and terrestrial radiation. This is quantified in the Single Scattering Albedo (SSA), the ratio of scattering alone to scattering plus absorption (extinction) of radiation by a particle. The SSA tends to unity if scattering dominates, with relatively little absorption, and decreases as absorption increases, becoming zero for infinite absorption. For example, sea-salt aerosol has an SSA of 1, as a sea-salt particle only scatters, whereas soot has an SSA of 0.23, showing that it is a major atmospheric aerosol absorber.

Aerosols, natural and anthropogenic, can affect the climate by changing the way radiation is transmitted through the atmosphere. Direct observations of the effects of aerosols are quite limited so any attempt to estimate their global effect necessarily involves the use of computer models. The Intergovernmental Panel on Climate Change, IPCC, says: While the radiative forcing due to greenhouse gases may be determined to a reasonably high degree of accuracy... the uncertainties relating to aerosol radiative forcings remain large, and rely to a large extent on the estimates from global modelling studies that are difficult to verify at the present time.However, they are mostly talking about tropospheric aerosol.

Effect on ozone

The aerosols have a role in the destruction of ozone due to surface chemistry effects.Destruction of ozone has in recent years created large holes in the ozone layer, initially over the Antarctic and then the Arctic. These holes in the ozone layer have the potential expand to cover inhabited and vegetative regions of the planet, leading to catastrophic environmental damage.

Ozone destruction occurs principally in polar regions, but the formation of ozone occurs principally in the tropics. Ozone is distributed around the planet by the Brewer-Dobson circulation. Therefore, the source and dispersal pattern of aerosols is critical in understanding their effect on the ozone layer.

Effect on sky appearance



Aerosols scatter light, which affects the appearance of the sky and of sunsets. Changing the concentration of aerosols in the atmosphere can dramatically affect the appearance of sunsets. A change in sky appearance during the year without a summer (attributed to the eruption of Tambora) was the inspiration for the paintings of J. M. W. Turner. Further volcanic eruptions and geoengineering projects involving sulfur aerosols are likely to affect the appearance of sunsets significantly, and to create a haze in the sky.

Effect on the biosphere

Aerosol particles are eventually deposited from the stratosphere onto land and ocean. Depending on the volume of particles descending, the effects may be significant to ecosystems, or may not be. Modelling of the quantities of aerosols used in likely geoengineering scenarios suggest that effects on terrestrial ecosystems from deposition is not likely to be significantly harmful.

Geoengineering

The ability of stratospheric sulfur aerosols to create this global dimming effect has made them a possible candidate for use in geoengineering projects to limit the effect and impact of climate change due to rising levels of greenhouse gases. Delivery of precursor gases such as H2S and SO2 by artillery, aircraft and balloons has been proposed.

Understanding of this proposed technique is partly based on the fact that it is the adaptation of an existing atmospheric process. The technique is therefore potentially better understood than are comparable (but purely speculative) geoengineering schemes. It is also partly based on the speed of action of any such solution deployed, in contrast to carbon sequestration projects such as carbon dioxide air capture which would take longer to work. However, gaps in understanding of these processes exist, for example the effect on stratospheric climate and on rainfall patterns, and further research is needed.

This technique has been studied more extensively than most other geoengineering techniques, and is suggested by commentators including Tom Wigley.

From http://en.wikipedia.org/

Step It Up 2007

Step It Up 2007 is a nationwide grassroots environmental campaign started by environmentalist Bill McKibben to demand action on global warming by the U.S. Congress.

Step It Up

In late summer 2006 McKibben helped lead a five-day walk across Vermont to demand action on global warming that some newspaper accounts called the largest demonstration to date in America about climate change. Beginning in January 2007, he founded Step It Up 2007, which organized rallies in hundreds of American cities and towns on April 14, 2007 to demand that Congress enact curbs on carbon emissions by 80 percent by 2050. The campaign quickly won widespread support from a wide variety of environmental, student, and religious groups, with 1400 rallies taking place.

Step It Up 2

In August 2007 McKibben announced Step It Up 2, to take place November 3, 2007. In addition to the 80% by 2050 slogan from the first campaign, the second adds "Green Jobs Now, and No New Coal,"

From http://en.wikipedia.org/

Space sunshade

A space sunshade or sunshield can be described as analogous to a parasol that diverts or otherwise reduces some of a star's rays, preventing them from hitting a planet and thereby reducing its insolation, which results in less heating of the planet. This can be of particular interest towards mitigating global warming through solar radiation management. Such shades could also be used to produce space solar power, acting as solar power satellites.

Cloud of small spacecraft near L1

One proposed such sunshade for use towards that effect would be composed of 16 trillion small disks at an altitude of 1.5 million kilometers, otherwise known as the L1 Orbit. A sunshade that blocks 2% of the sunlight, reflecting it off into space, would be enough to halt global warming, giving us ample time to cut our emissions back on earth.



Such a sunshade would have a diameter of 1800 km; it would cost tens of trillions of dollars to get the disks into space. It has been proposed that this would be accomplished most easily with a large railgun or coilgun which fires a capsule containing a million 1-gram shades into space.

Even so, it would still take years to launch enough of the disks into orbit before they have any effect. Thus, if using this technology should become essential, enough time would be needed to implement it.

Roger Angel of the University of Arizona presented the idea for the Sunshade at the U.S. National Academy of Sciences in April, 2006 and won a NASA Institute for Advanced Concepts grant for further research in July, 2006. His team members working on the grant are David Miller of the Massachusetts Institute of Technology, Nick Woolf of UA's Steward Observatory, and NASA Ames Research Center Director S. Pete Worden.

Creating this sunshade in space was estimated to cost in excess of US$5 trillion, thus leading Professor Angel to conclude that "the sunshade is no substitute for developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out."

From http://en.wikipedia.org/

Solar radiation management

Solar radiation management (SRM) projects are a type of geoengineering which seek to reflect sunlight and thus reduce global warming. They do not reduce greenhouse gas concentrations in the atmosphere, and thus do not address problems such as ocean acidification caused by these gases. Their principle advantage as an approach to geoengineering is the speed with which they can be deployed and become fully active. By comparison, other geoengineering techniques based on greenhouse gas remediation, such as ocean iron fertilization need to sequester the anthropogenic carbon excess before they can arrest global warming. Solar radiation management projects can therefore be used as a geoengineering 'quick fix' while levels of greenhouse gases can be brought under control by greenhouse gas remediation techniques.

A study by Lenton and Vaughan suggest that marine cloud brightening and stratospheric sulfur aerosols are each capable of reversing the warming effect of a doubling of the level of CO2 in the atmosphere when compared to pre-industrial levels.

Background

The phenomenon of global dimming is widely-known, and is not necessarily a geoengineering technique. It occurs in normal conditions, due to aerosols caused by pollution, or caused naturally as a result of volcanoes and major forest fires. However, its deliberate manipulation is a tool of the geoengineer. The majority of recent global dimming has been in the troposphere, except that resulting from volcanos, which affect mainly the stratosphere.

By intentionally changing the Earth's albedo, or reflectivity, scientists propose that we could reflect more heat back out into space, or intercept sunlight before it reaches the Earth through a literal shade built in space. A 0.5% albedo increase would roughly halve the effect of CO2 doubling.

The idea goes back at least to Hoyle (1957) and was expanded on by Kahle and Deirmendjian (1973) of Rand Corporation.

As early as 1974, Russian expert Mikhail Budyko suggested that if global warming became a problem, we could cool down the planet by burning sulfur in the stratosphere, which would create a haze. Paul Crutzen suggests that this would cost 25 to 50 billion dollars per year. It would, however, increase the environmental problem of acid rain. However, this is now believed to be a minor side effect.

These geoengineering projects have been proposed in order to reduce global warming. The effect of rising greenhouse gas concentrations in the atmosphere on global climate is to create a warming effect on the planet. By modifying the albedo (whiteness) of the Earth's surface, or by preventing sunlight reaching the Earth by using a solar shade, this warming effect can be cancelled out - although it should be noted that the cancellation is imperfect, with time of day and regional discrepancies remaining.

The applicability of many techniques listed here has not been comprehensively tested. Even if the effects of small-scale interventions are known, there may be cumulative problems such as ozone depletion, which only become apparent from large scale experiments.

Various small-scale experiments have been carried out on techniques such as cloud seeding, increasing the volume of stratospheric sulfur aerosols and implementing cool roof technology.

A preliminary study by Edward Teller and others in 2002 presented the pros and cons of various relatively "low-tech" proposals to mitigate global warming through scattering/reflecting sunlight away from the Earth via insertion of various materials in the upper stratosphere, low earth orbit, and L1 locations.

Limitations

As well as the imperfect cancellation of the effect of greenhouse gases on global warming, there are other significant problems with solar radiation management as a from of geoengineering not least of these are effects on the global hydrological cycle and the inability of such techniques to reduce ocean acidification. A comprehensive list of problems with geoengineering is available here

However, it should be noted that this type of geoengineering can have indirect benefits, such as keeping permafrost frozen and thus keeping methane locked up within it.

Atmospheric projects

These projects seek to modify the atmosphere, either by enhancing natural processes such as the sulfur cycle, or by using artificial techniques such as reflective balloons.

Stratospheric sulfur aerosols

Stratospheric sulfur aerosols: proposed by Paul Crutzen, with the purpose to modify the Earth's albedo with reflective or absorptive materials spread over portions of its surface. This would typically be achieved using hydrogen sulfide or sulfur dioxide, delivered using artillery, aircraft (such as the high-flying F15-C) or balloons. Ozone depletion is a risk of such techniques, but only if high enough quantities of aerosols drift to, or are deposited in, polar stratospheric clouds before the levels of CFCs and other ozone destroying gases fall naturally to safe levels. This proposal, not unlike the others, carries with it considerable risks, including increased drought or acid rain. Broadly speaking, this technique is seen as a credible geoengineering scheme, although not one without major risks, and challenges for its implementation. This technique can give >3.7W/m2 of globally-averaged negative forcing, which is sufficient to entirely offset the warming caused by a doubling of CO2.

Reflective aerosols or dust

Methods based on increasing the aerosol content in the lower stratosphere for climate modification were proposed by a Russian scientist, Budyko.

United States Patent 5003186 suggested that tiny metal flakes could be "added to the fuel of jet airliners, so that the particles would be emitted from the jet engine exhaust while the airliner was at its cruising altitude." Alternative proposals, not known to have been published in peer-reviewed journals, include the addition of silicon compounds to jet fuel to make silicon dioxide particles in the exhaust.

Alleged secret experiments with aircraft exhaust modification are referred to as the 'Chemtrail Mystery'. or Chemtrail conspiracy theory.

In 1992, a report by the US National Academy of Sciences (NAS) on geoengineering noted that dust is a better choice compared to sulphur, because dust is from natural soil and so should have no noticeable effect on the ground as it gradually falls into the troposphere and rains out. It estimated that about 1010 kg dust would be required to mitigate the warming from a doubling of atmospheric CO2 or about 1 kg dust per 100 t of carbon emissions.

An example of the effects of the imposition of aerosol particles in the atmosphere can be found in history. Comets have been blamed for the dramatic but brief cooling period which commenced in 1159 BCE, and resulted in widespread disruption to civilisations at the time. However, this mechanism, and even the involvement of a comet, is not universally accepted. If a comet was indeed to blame, the action of its aerosols could also have been by the mechanism of cloud condensation nuclei. Other examples of climate change events linked to comets include the famines around 536 CE.

Cloud whitening / marine cloud brightening / cloud reflectivity enhancement



Various schemes have been suggested, such as that proposed by John Latham and Stephen Salter, which works by spraying seawater in the atmosphere to increase the reflectiveness of clouds. The extra condensation nuclei created by the spray will change the size distribution of the drops in existing clouds to make them whiter. The sprayers would use fleets of unmanned Rotor ships known as Flettner vessels to spray mist created from seawater into the air to thicken clouds and thus reflect more radiation from the Earth. The whitening effect is created by using very small cloud condensation nuclei, which whiten the clouds due to the Twomey effect.

This technique can give >3.7W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of a doubling of CO2.

Ocean sulfur cycle enhancement

Enhancing the natural sulfur cycle in the Southern Ocean ocean by fertilizing a small portion with iron in order to enhance dimethyl sulfide production and cloud reflectivity. The goal is to slow Antarctic ice from melting and raising sea level. Such techniques also tend to sequester carbon, but in this specific project the enhancement of cloud albedo was both the desired outcome and measured result. An alternative technique proposes the vertical mixing of ocean water, to bring deep-water nutrients to surface plankton. This technique can give only 0.016W/m2 of globally-averaged negative forcing, which is essentially insignificant for geoengineering purposes.

Reflective balloons

Place billions of aluminized, hydrogen-filled balloons in the stratosphere has been suggested to provide a reflective screen.

These reflectors would be placed at a high enough altitude so that they do not interfere with air traffic. The cost estimate is about 20 times as much as the distribution of dust in the stratosphere, making these schemes economically nonviable. The large number of reflectors and the trash problem posed by their fall make the system unattractive.

Low stratospheric soot

Decreasing the efficiency of burning in engines of aircraft flying in the low stratosphere would maintain a thin cloud of soot to intercept sunlight. However, the relationship between soot or other combustion products and climate change is complex, with some types causing a warming effect. Almost all aircraft cannot reach the stratosphere in most parts of the world.

Cloud seeding

Cloud stimulation can be carried out using a variety of methods, such as burning sulfur in ships or power plants to form sulfate aerosol in order to stimulate additional low marine clouds to reflect sunlight. Liquid nitrogen can also be used, as can silver iodide "Earlier, Reck (1978) studied the effect of increases in cloud cover and, using a radiative-convective atmospheric model, found that a 4 to 5 percent increase in low-level cloud cover would be sufficient to offset the warming predicted from a doubling of preindustrial CO2. This value is in reasonable agreement with Randall et al. (1984), who estimated that a 4 percent increase was required in the amount of marine stratocumulus, which comprises the bulk of the low clouds on a global basis."

Terrestrial albedo modification

Cool roof



Painting pavements and roof materials in white or pale colours to reflect solar radiation, known as 'cool roof' technology, and encouraged by legislation in some areas (notably California).This is a benign technique, although limited in its ultimate effectiveness by the costrained surface area available for treatment. This technique can give between 0.01-0.19W/m2 of globally-averaged negative forcing, depending on whether cities or all settlements are so treated.This is generally insignificant when compared to the 3.7W/m2 of positive forcing from a doubling of CO2. However, in many cases it can be achieved at little or no cost by simply selecting different materials. Further, it can reduce the need for air conditioning, which causes CO2 emissions which worsen global warming. For this reason alone it is still demonstrably worth pursuing.

Reflective sheeting

Reflective plastic sheets covering 67,000 square miles of desert, to reflect the Sun’s energy. This technique can give globally-averaged 1.74W/m2 of negative forcing, which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but is still a very significant contribution and is sufficient to offset the current level of warming (approx. 1.7W/m2). However, the effect would be strongly regional, and would not be ideal for controlling Arctic shrinkage, which is one of the most significant problems resulting from global warming.

Ocean litter

An early geoengineering idea was to use pale coloured floating litter within certain stable oceanic gyres. This litter would tend to group into large and stable areas, such as the Great Pacific Garbage Patch.

Farming, forestry, and land management

Forestry

Reforestation in tropical areas has a cooling effect. Deforestation of high-latitude and high-altitude forests exposes snow and this increases albedo.

Grassland management

Changes to grassland have been proposed to increase albedo. This technique can give 0.64W/m2 of globally-averaged negative forcing, which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but could make a minor contribution towards it.

High-albedo crop varieties

Selecting or genetically-modifying commercial crops with high albedo has been suggested.This has the advantage of being relatively simple to implement, with farmers simply switching from one variety to another. Temperate areas may experience a 1°C cooling as a result of this technique. This technique is an example of bio-geoengineering. This technique can give 0.44W/m2 of globally-averaged negative forcing, which is insufficient to offset the 3.7W/m2 of positive forcing from a doubling of CO2, but could make a minor contribution towards it.

Space projects

Space-based geoengineering projects are seen by many commentators and scientists as being far-fetched at present.

Space mirrors

Mirrors in space: proposed by Roger Angel with the purpose to deflect a percentage of solar sunlight into space, using mirrors orbiting around the Earth.

Moon dust

Mining moon dust to create a shielding cloud was proposed by Curtis Struck at Iowa State University in Ames

Dispersive solutions



Several authors have proposed dispersing light before it reaches the Earth by putting a very large diffraction grating or lens in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early, and in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde. In 2004, physicist and science fiction author Gregory Benford calculated that a concave rotating Fresnel lens 1000 kilometres across, yet only a few millimeters thick, floating in space at the L1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. He estimated that this would cost around US$10 billion up front, and another $10 billion in supportive cost during its lifespan. Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water that could be disastrous to ocean life.

Putting a very large diffraction grating (thin wire mesh) or lens in space, perhaps at the L1 point between the Earth and the Sun.

From http://en.wikipedia.org/

Season creep

In phenology, season creep is a neologism that refers to observed changes in the timing of the seasons, especially earlier indications of spring widely observed in temperate areas across the Northern Hemisphere. Phenological records analyzed by climate scientists have shown significant temporal trends in the observed time of seasonal events, from the end of the 20th century and continuing into the 21st century. In Europe, season creep has been associated with the arrival of spring moving up by approximately one week in a recent 30 year period. Other studies have put the rate of season creep measured by plant phenology in the range of 2–3 days per decade advancement in spring, and 0.3–1.6 days per decade delay in autumn, over the past 30–80 years.

Observable changes in nature related to season creep include birds laying their eggs earlier and buds appearing on some trees in late winter. In addition to advanced budding, flowering trees have been blooming earlier, for example the culturally important cherry blossoms in Japan, and Washington, D.C. Northern hardwood trees have been trending toward leafing out sooner, and retaining their green canopies longer. The agricultural growing season has also expanded by 10–20 days over the last few decades.

The effects of season creep have been noted by non-scientists as well, including gardeners who have advanced their spring planting times, and experimented with plantings of less hardy warmer climate varieties of non-native plants. While summer growing seasons are expanding, winters are getting warmer and shorter, resulting in reduced winter ice cover on bodies of water, earlier ice-out, earlier melt water flows, and earlier spring lake level peaks. Some spring events, or "phenophases", have become intermittent or unobservable; for example, bodies of water that once froze regularly most winters now freeze less frequently, and formerly migratory birds are now seen year-round in some areas.

Relationship to global warming

The full impact of global warming is forecast to happen in the future, but climate scientists have cited season creep as an easily observable effect of climate change that has already occurred. A large systematic phenological examination of data on 542 plant species in 21 European countries from 1971–2000 showed that 78% of all leafing, flowering, and fruiting records advanced while only 3% were significantly delayed, and these observations were consistent with measurements of observed warming. Similar changes in the phenology of plants and animals are occurring across marine, freshwater, and terrestrial groups studied, and these changes are also consistent with the expected impact of global warming.

While phenology fairly consistently points to an earlier spring across temperate regions of North America, a recent comprehensive study of the sub-arctic showed greater variability in the timing of green-up, with some areas advancing, and some having no discernible trend over a recent 44-year period. Another 40 year phenological study in China found greater warming over that period in the more northerly sites studied, with sites experiencing cooling mostly in the south, indicating that the temperature variation with latitude is decreasing there. This study also confirmed that season creep was correlated with warming, but the effect is non-linear—phenophases advanced less with greater warming, and retarded more with greater cooling.

Shorter winters and longer growing seasons may appear to be a benefit to society from global warming, but the effects of advanced phenophases may also have serious consequences for human populations. Modeling of snowmelt predicted that warming of 3° to 5°C in the Western United States could cause snowmelt-driven runoff to occur as much as two months earlier, with profound effects on hydroelectricity, land use, agriculture, and water management. Since 1980, earlier snowmelt and associated warming has also been associated with an increase in length and severity of the wildfire season there.

From http://en.wikipedia.org/

Scientific opinion on climate change

National and international science academies and professional societies have assessed the current scientific opinion, in particular on recent global warming. These assessments have largely followed or endorsed the Intergovernmental Panel on Climate Change (IPCC) position of January 2001 that states:

An increasing body of observations gives a collective picture of a warming world and other changes in the climate system... There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.

Since 2007, no scientific body of national or international standing has maintained a dissenting opinion. A few organisations hold non-committal positions.

Synthesis reports

Synthesis reports are assessments of scientific literature that compile the results of a range of stand-alone studies in order to achieve a broad level of understanding, or to describe the state of knowledge of a given subject.

Intergovernmental Panel on Climate Change (IPCC) 2007

In February 2007, the IPCC released a summary of the forthcoming Fourth Assessment Report. According to this summary, the Fourth Assessment Report finds that human actions are "very likely" the cause of global warming, meaning a 90% or greater probability. Global warming in this case is indicated by an increase of 0.75 degrees in average global temperatures over the last 100 years.

The New York Times reported:

The world's leading climate scientists said global warming has begun, is very likely caused by man, and will be unstoppable for centuries.... The phrase very likely translates to a more than 90 percent certainty that global warming is caused by man's burning of fossil fuels. That was the strongest conclusion to date, making it nearly impossible to say natural forces are to blame.

The report said that an increase in hurricane and tropical cyclone strength since 1970 more likely than not can be attributed to man-made global warming. The scientists said global warming's connection varies with storms in different parts of the world, but that the storms that strike the Americas are global warming-influenced.

The Associated Press summarized the position on sea level rise:

On sea levels, the report projects rises of 7-23 inches by the end of the century. That could be augmented by an additional 4-8 inches if recent polar ice sheet melt continues.

U.S. Global Change Research Program

formerly the Climate Change Science Program

The U.S. Global Change Research Program reported in June, 2009 that:

Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities.

The report, which is about the effects that climate change is having in the United States, also says:

Climate-related changes have already been observed globally and in the United States. These include increases in air and water temperatures,reduced frost days, increased frequency and intensity of heavy downpours, a rise in sea level, and reduced snow cover, glaciers, permafrost, and sea ice. A longer ice-free period on lakes and rivers, lengthening of the growing season, and increased water vapor in the atmosphere have also been observed. Over the past 30 years, temperatures have risen faster in winter than in any other season, with average winter temperatures in the Midwest and northern Great Plains increasing more than 7°F. Some of the changes have been faster than previous assessments had suggested.

Arctic Climate Impact Assessment

In 2004, the intergovernmental Arctic Council and the non-governmental International Arctic Science Committee released the synthesis report of the Arctic Climate Impact Assessment:

Climate conditions in the past provide evidence that rising atmospheric carbon dioxide levels are associated with rising global temperatures. Human activities, primarily the burning of fossil fuels (coal, oil, and natural gas), and secondarily the clearing of land, have increased the concentration of carbon dioxide, methane, and other heat-trapping ("greenhouse") gases in the atmosphere...There is international scientific consensus that most of the warming observed over the last 50 years is attributable to human activities.

Statements by concurring organizations

Academies of Science

European Academy of Sciences and Arts

In 2007, the European Academy of Sciences and Arts issued a formal declaration on climate change titled Let's Be Honest:

Human activity is most likely responsible for climate warming. Most of the climatic warming over the last 50 years is likely to have been caused by increased concentrations of greenhouse gases in the atmosphere. Documented long-term climate changes include changes in Arctic temperatures and ice, widespread changes in precipitation amounts, ocean salinity, wind patterns and extreme weather including droughts, heavy precipitation, heat waves and the intensity of tropical cyclones. The above development potentially has dramatic consequences for mankind’s future.

InterAcademy Council

As the representative of the world’s scientific and engineering academies, the InterAcademy Council (IAC) issued a report in 2007 titled Lighting the Way: Toward a Sustainable Energy Future.

Current patterns of energy resources and energy usage are proving detrimental to the long-term welfare of humanity. The integrity of essential natural systems is already at risk from climate change caused by the atmospheric emissions of greenhouse gases.

Concerted efforts should be mounted for improving energy efficiency and reducing the carbon intensity of the world economy.

International Council of Academies of Engineering and Technological Sciences

In 2007, the International Council of Academies of Engineering and Technological Sciences (CAETS) issued a Statement on Environment and Sustainable Growth

As reported by the Intergovernmental Panel on Climate Change (IPCC), most of the observed global warming since the mid-20th century is very likely due to human-produced emission of greenhouse gases and this warming will continue unabated if present anthropogenic emissions continue or, worse, expand without control.

CAETS, therefore, endorses the many recent calls to decrease and control greenhouse gas emissions to an acceptable level as quickly as possible.

Joint science academies' statements

Since 2001, 32 national science academies have come together to issue joint declarations confirming anthropogenic global warming, and urging the nations of the world to reduce emissions of greenhouse gases. The signatories of these statements have been the national science academies of Australia, Belgium, Brazil, Cameroon, Canada, the Caribbean, China, France, Ghana, Germany, Indonesia, Ireland, Italy, India, Japan, Kenya, Madagascar, Malaysia, Mexico, Nigeria, New Zealand, Russia, Senegal, South Africa, Sudan, Sweden, Tanzania, Uganda, United Kingdom, United States, Zambia, and Zimbabwe.

* 2001-Following the publication of the IPCC Third Assessment Report, sixteen national science academies issued a joint statement explicitly acknowledging the IPCC position as representing the scientific consensus on climate change science. The sixteen science academies that issued the statement were those of Australia, Belgium, Brazil, Canada, the Caribbean, China, France, Germany, India, Indonesia, Ireland, Italy, Malaysia, New Zealand, Sweden, and the United Kingdom.

* 2005-The national science academies of the G8 nations, plus Brazil, China and India, three of the largest emitters of greenhouse gases in the developing world, signed a statement on the global response to climate change. The statement stresses that the scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action, and explicitly endorsed the IPCC consensus. The eleven signatories were the science academies of Brazil, Canada, China, France, Germany, India, Italy, Japan, Russia, the United Kingdom, and the United States.

* 2007-In preparation for the 2007 G8 summit, the national science academies of the G8+5 nations issued a declaration referencing the position of the 2005 joint science academies' statement, and acknowledging the confirmation of their previous conclusion by recent research. Following the IPCC Fourth Assessment Report, the declaration states, "It is unequivocal that the climate is changing, and it is very likely that this is predominantly caused by the increasing human interference with the atmosphere. These changes will transform the environmental conditions on Earth unless counter-measures are taken." The thirteen signatories were the national science academies of Brazil, Canada, China, France, Germany, Italy, India, Japan, Mexico, Russia, South Africa, the United Kingdom, and the United States.

* 2008-In preparation for the 34th G8 summit, the national science academies of the G8+5 nations issued a declaration reiterating the position of the 2005 joint science academies’ statement, and reaffirming “that climate change is happening and that anthropogenic warming is influencing many physical and biological systems.” Among other actions, the declaration urges all nations to “(t)ake appropriate economic and policy measures to accelerate transition to a low carbon society and to encourage and effect changes in individual and national behaviour.”The thirteen signatories were the same national science academies that issued the 2007 joint statement.

* 2009-In advance of the UNFCCC negotiations to be held in Copenhagen in December 2009, the national science academies of the G8+5 nations issued a joint statement declaring, "Climate change and sustainable energy supply are crucial challenges for the future of humanity. It is essential that world leaders agree on the emission reductions needed to combat negative consequences of anthropogenic climate change". The statement references the IPCC's Fourth Assessment of 2007, and asserts that "climate change is happening even faster than previously estimated; global CO2 emissions since 2000 have been higher than even the highest predictions, Arctic sea ice has been melting at rates much faster than predicted, and the rise in the sea level has become more rapid." The thirteen signatories were the same national science academies that issued the 2007 and 2008 joint statements.

Network of African Science Academies

In 2007, the Network of African Science Academies submitted a joint “statement on sustainability, energy efficiency, and climate change” to the leaders meeting at the G8 Summit in Heiligendamm, Germany:

“A consensus, based on current evidence, now exists within the global scientific community that human activities are the main source of climate change and that the burning of fossil fuels is largely responsible for driving this change.”

“The IPCC should be congratulated for the contribution it has made to public understanding of the nexus that exists between energy, climate and sustainability.”

The thirteen signatories were the science academies of Cameroon, Ghana, Kenya, Madagascar, Nigeria, Senegal, South Africa, Sudan, Tanzania, Uganda, Zambia, Zimbabwe, as well as the African Academy of Sciences.

Royal Society of New Zealand

Having signed onto the first joint science academies' statement in 2001, the Royal Society of New Zealand released a separate statement in 2008 in order to clear up "the controversy over climate change and its causes, and possible confusion among the public":

The globe is warming because of increasing greenhouse gas emissions. Measurements show that greenhouse gas concentrations in the atmosphere are well above levels seen for many thousands of years. Further global climate changes are predicted, with impacts expected to become more costly as time progresses. Reducing future impacts of climate change will require substantial reductions of greenhouse gas emissions.

Polish Academy of Sciences

In December 2007, the General Assembly of the Polish Academy of Sciences (PAN) issued a statement endorsing the IPCC conclusions, and states:

"it is the duty of Polish science and the national government to, in a thoughtful, organized and active manner, become involved in realisation of these ideas".

"Problems of global warming, climate change, and their various negative impacts on human life and on the functioning of entire societies are one of the most dramatic challenges of modern times."

"PAS General Assembly calls on the national scientific communities and the national government to actively support Polish participation in this important endeavor."

General science

American Association for the Advancement of Science

In 2006, the American Association for the Advancement of Science adopted an official statement on climate change in which they stated, "The scientific evidence is clear: global climate change caused by human activities is occurring now, and it is a growing threat to society....The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now."

European Science Foundation

In 2007, the European Science Foundation issued a Position Paper on climate change:

There is now convincing evidence that since the industrial revolution, human activities, resulting in increasing concentrations of greenhouse gases have become a major agent of climate change. These greenhouse gases affect the global climate by retaining heat in the troposphere, thus raising the average temperature of the planet and altering global atmospheric circulation and precipitation patterns.
While on-going national and international actions to curtail and reduce greenhouse gas emissions are essential, the levels of greenhouse gases currently in the atmosphere, and their impact, are likely to persist for several decades. On-going and increased efforts to mitigate climate change through reduction in greenhouse gases are therefore crucial.

National Research Council (US)

In 2001, the Committee on the Science of Climate Change of the National Research Council published Climate Change Science: An Analysis of Some Key Questions. This report explicitly endorses the IPCC view of attribution of recent climate change as representing the view of the scientific community:

The changes observed over the last several decades are likely mostly due to human activities, but we cannot rule out that some significant part of these changes is also a reflection of natural variability. Human-induced warming and associated sea level rises are expected to continue through the 21st century... The IPCC's conclusion that most of the observed warming of the last 50 years is likely to have been due to the increase in greenhouse gas concentrations accurately reflects the current thinking of the scientific community on this issue.

Biology and life sciences

American Association of Wildlife Veterinarians

The American Association of Wildlife Veterinarians (AAWV) has issued a position statement regarding "climate change, wildlife diseases, and wildlife health":

There is widespread scientific agreement that the world’s climate is changing and that the weight of evidence demonstrates that anthropogenic factors have and will continue to contribute significantly to global warming and climate change. It is anticipated that continuing changes to the climate will have serious negative impacts on public, animal and ecosystem health due to extreme weather events, changing disease transmission dynamics, emerging and re-emerging diseases, and alterations to habitat and ecological systems that are essential to wildlife conservation. Furthermore, there is increasing recognition of the inter-relationships of human, domestic animal, wildlife, and ecosystem health as illustrated by the fact the majority of recent emerging diseases have a wildlife origin.

American Society for Microbiology

In 2003, the American Society for Microbiology issued a public policy report in which they recommend “reducing net anthropogenic CO2 emissions to the atmosphere” and “minimizing anthropogenic disturbances of” atmospheric gasses:

Carbon dioxide concentrations were relatively stable for the past 10,000 years but then began to increase rapidly about 150 years ago…as a result of fossil fuel consumption and land use change.

Of course, changes in atmospheric composition are but one component of global change, which also includes disturbances in the physical and chemical conditions of the oceans and land surface. Although global change has been a natural process throughout Earth’s history, humans are responsible for substantially accelerating present-day changes. These changes may adversely affect human health and the biosphere on which we depend.

Outbreaks of a number of diseases, including Lyme disease, hantavirus infections, dengue fever, bubonic plague, and cholera, have been linked to climate change.

Australian Coral Reef Society

In 2006, the Australian Coral Reef Society issued an official communique regarding the Great Barrier Reef and the "world-wide decline in coral reefs through processes such as overfishing, runoff of nutrients from the land, coral bleaching, global climate change, ocean acidification, pollution", etc.:

There is almost total consensus among experts that the earth’s climate is changing as a result of the build-up of greenhouse gases. The IPCC (involving over 3,000 of the world’s experts) has come out with clear conclusions as to the reality of this phenomenon. One does not have to look further than the collective academy of scientists worldwide to see the string (of) statements on this worrying change to the earth’s atmosphere.

There is broad scientific consensus that coral reefs are heavily affected by the activities of man and there are significant global influences that can make reefs more vulnerable such as global warming....It is highly likely that coral bleaching has been exacerbated by global warming.

Institute of Biology (UK)

The UK's Institute of Biology states “there is scientific agreement that the rapid global warming that has occurred in recent years is mostly anthropogenic, ie due to human activity.” As a consequence of global warming, they warn that a “rise in sea levels due to melting of ice caps is expected to occur. Rises in temperature will have complex and frequently localised effects on weather, but an overall increase in extreme weather conditions and changes in precipitation patterns are probable, resulting in flooding and drought. The spread of tropical diseases is also expected.” Subsequently, the Institute of Biology advocates policies to reduce “greenhouse gas emissions, as we feel that the consequences of climate change are likely to be severe.”

Society of American Foresters

In 2008, the Society of American Foresters (SAF) issued two position statements pertaining to climate change in which they cite the IPCC and the UNFCCC:

Forests are shaped by climate....Changes in temperature and precipitation regimes therefore have the potential to dramatically affect forests nationwide. There is growing evidence that our climate is changing. The changes in temperature have been associated with increasing concentrations of atmospheric carbon dioxide (CO2) and other GHGs in the atmosphere.

Forests play a significant role in offsetting CO2 emissions, the primary anthropogenic GHG.

The Wildlife Society (international)

The Wildlife Society has issued a position statement titled Global Climate Change and Wildlife:

Scientists throughout the world have concluded that climate research conducted in the past two decades definitively shows that rapid worldwide climate change occurred in the 20th century, and will likely continue to occur for decades to come. Although climates have varied dramatically since the earth was formed, few scientists question the role of humans in exacerbating recent climate change through the emission of greenhouse gases. The critical issue is no longer “if” climate change is occurring, but rather how to address its effects on wildlife and wildlife habitats.

The statement goes on to assert that “evidence is accumulating that wildlife and wildlife habitats have been and will continue to be significantly affected by ongoing large-scale rapid climate change.”

The statement concludes with a call for “reduction in anthropogenic (human-caused) sources of carbon dioxide and other greenhouse gas emissions contributing to global climate change and the conservation of CO2- consuming photosynthesizers (i.e., plants).”

Earth sciences

American Geophysical Union

The American Geophysical Union (AGU) statement, adopted by the society in 2003 and revised in 2007, affirms that rising levels of greenhouse gases have caused and will continue to cause the global surface temperature to be warmer:

The Earth's climate is now clearly out of balance and is warming. Many components of the climate system—including the temperatures of the atmosphere, land and ocean, the extent of sea ice and mountain glaciers, the sea level, the distribution of precipitation, and the length of seasons—are now changing at rates and in patterns that are not natural and are best explained by the increased atmospheric abundances of greenhouse gases and aerosols generated by human activity during the 20th century. Global average surface temperatures increased on average by about 0.6°C over the period 1956–2006. As of 2006, eleven of the previous twelve years were warmer than any others since 1850. The observed rapid retreat of Arctic sea ice is expected to continue and lead to the disappearance of summertime ice within this century. Evidence from most oceans and all continents except Antarctica shows warming attributable to human activities. Recent changes in many physical and biological systems are linked with this regional climate change. A sustained research effort, involving many AGU members and summarized in the 2007 assessments of the Intergovernmental Panel on Climate Change, continues to improve our scientific understanding of the climate.

European Federation of Geologists

In 2008, the European Federation of Geologists (EFG) issued the position paper Carbon Capture and geological Storage :

The EFG recognizes the work of the IPCC and other organizations, and subscribes to the major findings that climate change is happening, is predominantly caused by anthropogenic emissions of CO2, and poses a significant threat to human civilization.

It is clear that major efforts are necessary to quickly and strongly reduce CO2 emissions. The EFG strongly advocates renewable and sustainable energy production, including geothermal energy, as well as the need for increasing energy efficiency.

CCS Carbon Capture and geological Storage should also be regarded as a bridging technology, facilitating the move towards a carbon free economy.

European Geosciences Union

In 2005, the Divisions of Atmospheric and Climate Sciences of the European Geosciences Union (EGU) issued a position statement in support of the joint science academies’ statement on global response to climate change. The statement refers to the Intergovernmental Panel on Climate Change (IPCC), as "the main representative of the global scientific community", and asserts that the IPCC “represents the state-of-the-art of climate science supported by the major science academies around the world and by the vast majority of science researchers and investigators as documented by the peer-reviewed scientific literature.”

Additionally, in 2008, the EGU issued a position statement on ocean acidification which states, "Ocean acidification is already occurring today and will continue to intensify, closely tracking atmospheric CO2 increase. Given the potential threat to marine ecosystems and its ensuing impact on human society and economy, especially as it acts in conjunction with anthropogenic global warming, there is an urgent need for immediate action." The statement then advocates for strategies "to limit future release of CO2 to the atmosphere and/or enhance removal of excess CO2 from the atmosphere."

Geological Society of America

In 2006, the Geological Society of America adopted a position statement on global climate change:

The Geological Society of America (GSA) supports the scientific conclusions that Earth’s climate is changing; the climate changes are due in part to human activities; and the probable consequences of the climate changes will be significant and blind to geopolitical boundaries. Furthermore, the potential implications of global climate change and the time scale over which such changes will likely occur require active, effective, long-term planning.

International Union of Geodesy and Geophysics

In July 2007, the International Union of Geodesy and Geophysics (IUGG) adopted a resolution titled “The Urgency of Addressing Climate Change”. In it, the IUGG concurs with the “comprehensive and widely accepted and endorsed scientific assessments carried out by the Intergovernmental Panel on Climate Change and regional and national bodies, which have firmly established, on the basis of scientific evidence, that human activities are the primary cause of recent climate change.” They state further that the “continuing reliance on combustion of fossil fuels as the world’s primary source of energy will lead to much higher atmospheric concentrations of greenhouse gasses, which will, in turn, cause significant increases in surface temperature, sea level, ocean acidification, and their related consequences to the environment and society.”

National Association of Geoscience Teachers

In July 2009, the National Association of Geoscience Teachers (NAGT) adopted a position statement on climate change in which they assert that "Earth's climate is changing and "that present warming trends are largely the result of human activities":

NAGT strongly supports and will work to promote education in the science of climate change, the causes and effects of current global warming, and the immediate need for policies and actions that reduce the emission of greenhouse gases.

Stratigraphy Commission of the Geological Society of London

In its position paper on global warming, the Stratigraphy Commission of the Geological Society of London declares, "Global climate change is increasingly recognised as the key threat to the continued development – and even survival - of humanity." They refer to the IPCC as providing the "most authoritative assessment of climate change", and further state, "We find that the evidence for human-induced climate change is now persuasive, and the need for direct action compelling."

Human health

American Academy of Pediatrics

In 2007, the American Academy of Pediatrics issued the policy statement Global Climate Change and Children's Health:

There is broad scientific consensus that Earth's climate is warming rapidly and at an accelerating rate. Human activities, primarily the burning of fossil fuels, are very likely (>90% probability) to be the main cause of this warming. Climate-sensitive changes in ecosystems are already being observed, and fundamental, potentially irreversible, ecological changes may occur in the coming decades. Conservative environmental estimates of the impact of climate changes that are already in process indicate that they will result in numerous health effects to children.

Anticipated direct health consequences of climate change include injury and death from extreme weather events and natural disasters, increases in climate-sensitive infectious diseases, increases in air pollution–related illness, and more heat-related, potentially fatal, illness. Within all of these categories, children have increased vulnerability compared with other groups.

American College of Preventive Medicine

In 2006, the American College of Preventive Medicine issued a policy statement on “Abrupt Climate Change and Public Health Implications”:

The American College of Preventive Medicine (ACPM) accept the position that global warming and climate change is occurring, that there is potential for abrupt climate change, and that human practices that increase greenhouse gases exacerbate the problem, and that the public health consequences may be severe.

American Medical Association

In 2008, the American Medical Association issued a policy statement on global climate change declaring that they:

Support the findings of the latest Intergovernmental Panel on Climate Change report, which states that the Earth is undergoing adverse global climate change and that these changes will negatively effect public health.

Support educating the medical community on the potential adverse public health effects of global climate change, including topics such as population displacement, flooding, infectious and vector-borne diseases, and healthy water supplies.

American Public Health Association

In 2007, the American Public Health Association issued a policy statement titled ‘’Addressing the Urgent Threat of Global Climate Change to Public Health and the Environment’’:

The long-term threat of global climate change to global health is extremely serious and the fourth IPCC report and other scientific literature demonstrate convincingly that anthropogenic GHG emissions are primarily responsible for this threat….US policy makers should immediately take necessary steps to reduce US emissions of GHGs, including carbon dioxide, to avert dangerous climate change.

Australian Medical Association

In 2004, the Australian Medical Association issued the position statement Climate Change and Human Health in which they recommend policies "to mitigate the possible consequential health effects of climate change through improved energy efficiency, clean energy production and other emission reduction steps."

This statement was revised again in 2008:

The world’s climate – our life-support system – is being altered in ways that are likely to pose significant direct and indirect challenges to health. While ‘climate change’ can be due to natural forces or human activity, there is now substantial evidence to indicate that human activity – and specifically increased greenhouse gas (GHGs) emissions – is a key factor in the pace and extent of global temperature increases.

Health impacts of climate change include the direct impacts of extreme events such as storms, floods, heatwaves and fires and the indirect effects of longer-term changes, such as drought, changes to the food and water supply, resource conflicts and population shifts.

Increases in average temperatures mean that alterations in the geographic range and seasonality of certain infections and diseases (including vector-borne diseases such as malaria, dengue fever, Ross River virus and food-borne infections such as Salmonellosis) may be among the first detectable impacts of climate change on human health.

Human health is ultimately dependent on the health of the planet and its ecosystem. The AMA believes that measures which mitigate climate change will also benefit public health. Reducing GHGs should therefore be seen as a public health priority.

European Centre for Disease Prevention and Control

In 2009, the European Centre for Disease Prevention and Control (ECDC) stated:

While climate variability is an ongoing process attributed to natural causes, climate change is ascribed to human activities that alter atmospheric conditions. These changes are due to anthropogenic activity such as the combustion of fossil fuels, which generates heat-trapping gases.
The impact on public health from climate change can be far reaching and include deaths and hospitalizations due to heat waves; hypothermia from blizzards; injuries and death from flooding; and the (re)emergence of hantavirus, West Nile virus, tick-borne encephalitis, Lyme disease, Malaria and Dengue.
Vector-borne diseases are transmitted by arthropods such as ticks (e.g. tick-borne encephalitis (TBE), Lyme disease), mosquitoes (e.g. Chikungunya fever, Dengue fever), or sandflies (e.g. visceral leishmaniasis). Climatic changes, such as hotter and longer summers, warmer winters, and/or increased annual rainfalls could enable these organisms to expand their habitats, thus introducing diseases to areas previously unfamiliar with them.

World Federation of Public Health Associations

In 2001, the World Federation of Public Health Associations issued a policy resolution on global climate change:

Noting the conclusions of the United Nations' Intergovernmental Panel on Climate Change (IPCC) and other climatologists that anthropogenic greenhouse gases, which contribute to global climate change, have substantially increased in atmospheric concentration beyond natural processes and have increased by 28 percent since the industrial revolution….Realizing that subsequent health effects from such perturbations in the climate system would likely include an increase in: heat-related mortality and morbidity; vector-borne infectious diseases,… water-borne diseases…(and) malnutrition from threatened agriculture….the World Federation of Public Health Associations…recommends precautionary primary preventive measures to avert climate change, including reduction of greenhouse gas emissions and preservation of greenhouse gas sinks through appropriate energy and land use policies, in view of the scale of potential health impacts....

World Health Organization

In 2008, the United Nations' World Health Organization issued their report Protecting health from climate change:

There is now widespread agreement that the earth is warming, due to emissions of greenhouse gases caused by human activity. It is also clear that current trends in energy use, development, and population growth will lead to continuing – and more severe – climate change.

The changing climate will inevitably affect the basic requirements for maintaining health: clean air and water, sufficient food and adequate shelter. Each year, about 800,000 people die from causes attributable to urban air pollution, 1.8 million from diarrhoea resulting from lack of access to clean water supply, sanitation, and poor hygiene, 3.5 million from malnutrition and approximately 60,000 in natural disasters. A warmer and more variable climate threatens to lead to higher levels of some air pollutants, increase transmission of diseases through unclean water and through contaminated food, to compromise agricultural production in some of the least developed countries, and increase the hazards of extreme weather.

Meteorology/oceanography

American Meteorological Society

The American Meteorological Society (AMS) statement adopted by their council in 2003 said:

There is now clear evidence that the mean annual temperature at the Earth's surface, averaged over the entire globe, has been increasing in the past 200 years. There is also clear evidence that the abundance of greenhouse gases in the atmosphere has increased over the same period. In the past decade, significant progress has been made toward a better understanding of the climate system and toward improved projections of long-term climate change... Human activities have become a major source of environmental change. Of great urgency are the climate consequences of the increasing atmospheric abundance of greenhouse gases... Because greenhouse gases continue to increase, we are, in effect, conducting a global climate experiment, neither planned nor controlled, the results of which may present unprecedented challenges to our wisdom and foresight as well as have significant impacts on our natural and societal systems.

Australian Meteorological and Oceanographic Society

The Australian Meteorological and Oceanographic Society has issued a Statement on Climate Change, wherein they conclude, “Global climate change and global warming are real and observable…It is highly likely that those human activities that have increased the concentration of greenhouse gases in the atmosphere have been largely responsible for the observed warming since 1950. The warming associated with increases in greenhouse gases originating from human activity is called the enhanced greenhouse effect. The atmospheric concentration of carbon dioxide has increased by more than 30% since the start of the industrial age and is higher now than at any time in at least the past 650,000 years. This increase is a direct result of burning fossil fuels, broad-scale deforestation and other human activity.”

Canadian Foundation for Climate and Atmospheric Sciences

In November 2005, the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS) issued a letter to the Prime Minister of Canada stating that "We concur with the climate science assessment of the Intergovernmental Panel on Climate Change (IPCC) in 2001 ... We endorse the conclusions of the IPCC assessment that 'There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities'. ... There is increasingly unambiguous evidence of changing climate in Canada and around the world. There will be increasing impacts of climate change on Canada’s natural ecosystems and on our socio-economic activities. Advances in climate science since the 2001 IPCC Assessment have provided more evidence supporting the need for action and development of a strategy for adaptation to projected changes."

Canadian Meteorological and Oceanographic Society

"CMOS endorses the process of periodic climate science assessment carried out by the Intergovernmental Panel on Climate Change and supports the conclusion, in its Third Assessment Report, which states that the balance of evidence suggests a discernible human influence on global climate."

Royal Meteorological Society (UK)

In February 2007, after the release of the IPCC’s Fourth Assessment Report, the Royal Meteorological Society issued an endorsement of the report. In addition to referring to the IPCC as “world’s best climate scientists”, they stated that climate change is happening as “the result of emissions since industrialization and we have already set in motion the next 50 years of global warming – what we do from now on will determine how worse it will get.”

World Meteorological Organization

In its Statement at the Twelfth Session of the Conference of the Parties to the U.N. Framework Convention on Climate Change presented on November 15, 2006, the World Meteorological Organization (WMO) confirms the need to “prevent dangerous anthropogenic interference with the climate system.” The WMO concurs that “scientific assessments have increasingly reaffirmed that human activities are indeed changing the composition of the atmosphere, in particular through the burning of fossil fuels for energy production and transportation.” The WMO concurs that “the present atmospheric concentration of CO2 was never exceeded over the past 420,000 years;” and that the IPCC “assessments provide the most authoritative, up-to-date scientific advice.”

Paleoclimatology

American Quaternary Association

The American Quaternary Association (AMQUA) has stated, “Few credible Scientists now doubt that humans have influenced the documented rise of global temperatures since the Industrial Revolution,” citing “the growing body of evidence that warming of the atmosphere, especially over the past 50 years, is directly impacted by human activity.”

International Union for Quaternary Research

The statement on climate change issued by the International Union for Quaternary Research reiterates the conclusions of the IPCC, and urges all nations to take prompt action in line with the UNFCCC principles.

“Human activities are now causing atmospheric concentrations of greenhouse gasses - including carbon dioxide, methane, tropospheric ozone, and nitrous oxide - to rise well above pre-industrial levels….Increases in greenhouse gasses are causing temperatures to rise…The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action….Minimizing the amount of this carbon dioxide reaching the atmosphere presents a huge challenge but must be a global priority.”

Miscellaneous

American Astronomical Society

The American Astronomical Society has endorsed the AGU statement:

In endorsing the "Human Impacts on Climate" statement issued by the American Geophysical Union, the AAS recognizes the collective expertise of the AGU in scientific subfields central to assessing and understanding global change, and acknowledges the strength of agreement among our AGU colleagues that the global climate is changing and human activities are contributing to that change.

American Chemical Society

The American Chemical Society stated:

Careful and comprehensive scientific assessments have clearly demonstrated that the Earth’s climate system is changing rapidly in response to growing atmospheric burdens of greenhouse gases and absorbing aerosol particles (IPCC, 2007). There is very little room for doubt that observed climate trends are due to human activities. The threats are serious and action is urgently needed to mitigate the risks of climate change.
The reality of global warming, its current serious and potentially disastrous impacts on Earth system properties, and the key role emissions from human activities play in driving these phenomena have been recognized by earlier versions of this ACS policy statement (ACS, 2004), by other major scientific societies, including the American Geophysical Union (AGU, 2003), the American Meteorological Society (AMS, 2007) and the American Association for the Advancement of Science (AAAS, 2007), and by the U. S. National Academies and ten other leading national academies of science (NA, 2005).

American Institute of Physics

The Governing Board of the American Institute of Physics endorsed the AGU statement on human-induced climate change:

The Governing Board of the American Institute of Physics has endorsed a position statement on climate change adopted by the American Geophysical Union (AGU) Council in December 2003.

American Physical Society

In November 2007, the American Physical Society (APS) adopted an official statement on climate change: "Emissions of greenhouse gases from human activities are changing the atmosphere in ways that affect the Earth's climate. Greenhouse gases include carbon dioxide as well as methane, nitrous oxide and other gases. They are emitted from fossil fuel combustion and a range of industrial and agricultural processes.

"The evidence is incontrovertible: Global warming is occurring. If no mitigating actions are taken, significant disruptions in the Earth’s physical and ecological systems, social systems, security and human health are likely to occur. We must reduce emissions of greenhouse gases beginning now."

American Statistical Association

On November 30, 2007, the American Statistical Association Board of Directors adopted a statement on climate change:

The ASA endorses the IPCC conclusions.... Over the course of four assessment reports, a small number of statisticians have served as authors or reviewers. Although this involvement is encouraging, it does not represent the full range of statistical expertise available. ASA recommends that more statisticians should become part of the IPCC process. Such participation would be mutually beneficial to the assessment of climate change and its impacts and also to the statistical community.

Engineers Australia (The Institution of Engineers Australia)

"Engineers Australia believes that Australia must act swiftly and proactively in line with global expectations to address climate change as an economic, social and environmental risk... We believe that addressing the costs of atmospheric emissions will lead to increasing our competitive advantage by minimising risks and creating new economic opportunities. Engineers Australia believes the Australian Government should ratify the Kyoto Protocol."

Noncommittal statements

American Association of State Climatologists

The Association has no current statement. The previous statement, discussed below, became inoperative in 2008. A committee has been formed to develop a new statement.

The 2001 statement from the American Association of State Climatologists noted the difficulties with predicting impacts due to climate change, while acknowledging that human activities are having an effect on climate:

Climate prediction is difficult because it involves complex, nonlinear interactions among all components of the earth’s environmental system.... The AASC recognizes that human activities have an influence on the climate system. Such activities, however, are not limited to greenhouse gas forcing and include changing land use and sulfate emissions, which further complicates the issue of climate prediction. Furthermore, climate predictions have not demonstrated skill in projecting future variability and changes in such important climate conditions as growing season, drought, flood-producing rainfall, heat waves, tropical cyclones and winter storms. These are the type of events that have a more significant impact on society than annual average global temperature trends. Policy responses to climate variability and change should be flexible and sensible – The difficulty of prediction and the impossibility of verification of predictions decades into the future are important factors that allow for competing views of the long-term climate future. Therefore, the AASC recommends that policies related to long-term climate not be based on particular predictions, but instead should focus on policy alternatives that make sense for a wide range of plausible climatic conditions regardless of future climate... Finally, ongoing political debate about global energy policy should not stand in the way of common sense action to reduce societal and environmental vulnerabilities to climate variability and change. Considerable potential exists to improve policies related to climate.

American Association of Petroleum Geologists

The American Association of Petroleum Geologists (AAPG) Position Statement on climate change states that "the AAPG membership is divided on the degree of influence that anthropogenic CO2 has on recent and potential global temperature increases ... Certain climate simulation models predict that the warming trend will continue, as reported through NAS, AGU, AAAS and AMS. AAPG respects these scientific opinions but wants to add that the current climate warming projections could fall within well-documented natural variations in past climate and observed temperature data. These data do not necessarily support the maximum case scenarios forecast in some models."

Prior to the adoption of this statement in June 2007, the AAPG was the only major scientific organization that rejected the finding of significant human influence on recent climate, according to a statement by the Council of the American Quaternary Association. Explaining the plan for a revision, AAPG president Lee Billingsly wrote in March 2007 that "Members have threatened to not renew their memberships... if AAPG does not alter its position on global climate change.... And I have been told of members who already have resigned in previous years because of our current global climate change position.... The current policy statement is not supported by a significant number of our members and prospective members."

American Geological Institute

In 1999, the American Geological Institute (AGI) issued the position statement ‘’Global Climate Change’’:

The American Geological Institute (AGI) strongly supports education concerning the scientific evidence of past climate change, the potential for future climate change due to the current building of carbon dioxide and other greenhouse gases, and the policy options available.

Understanding the interactions between the solid Earth, the oceans, the biosphere, and the atmosphere both in the present and over time is critical for accurately analyzing and predicting global climate change due to natural processes and possible human influences.

American Institute of Professional Geologists

In 2009, the American Institute of Professional Geologists (AIPG) sent a statement to President Barack Obama and other US government officials:

The geological professionals in AIPG recognize that climate change is occurring and has the potential to yield catastrophic impacts if humanity is not prepared to address those impacts. It is also recognized that climate change will occur regardless of the cause. The sooner a defensible scientific understanding can be developed, the better equipped humanity will be to develop economically viable and technically effective methods to support the needs of society.

Geological Committee of the Polish Academy of Sciences

In February 2009, the Committee of Geological Sciences of the Polish Academy of Sciences released the statement "Attitude of the Committee of Geological Sciences of the Polish Academy of Sciences to the question of impending of global warming" which states in part

Considerable restraint is desirable if ascribing exclusive or predominant responsibility to man for increased emission of greenhouse gases. The reality of such arbitrary statement on human influence has not been demonstrated...During the last 400 thousand years – still without anthropogenic greenhouse influence – the content of carbon dioxide in the air, as indicated by ice cores from Antarctica, was repeatedly 4 times at similar or even slightly higher level than at present.

It continues

It is certain that increased content of greenhouse gases in the atmosphere is connected partly with human activity. Therefore, all steps that restrain this emission and agree with principles of sustainable development should be taken, starting from a cease of extensive deforestation, especially in tropical areas. Various adapting measures that can mitigate effects of the recent trend of climate warming should be implemented by political decision makers.

The Committee on Geological Sciences is one of 90 committees of the Polish Academy of Sciences, and part of its Division of Earth and Mining Sciences.

Canadian Federation of Earth Sciences

In 2001, the Canadian Federation of Earth Sciences issued the position paper Mitigating climate change: Putting our carbon dioxide back into the ground:

We contribute to the global problem of changing climate by our emissions of greenhouse gases - especially carbon dioxide – from industrial processes. A warming Earth has significant problems for Canada – instability in agricultural productivity, sinking of northern infrastructrure into melting permafrost, greater vulnerability of low-lying coastlines to storms.

While the Canadian Geoscience Council is not at this time taking a particular position specifically on the issue of global warming, the Council is establishing a position on the use of geological sinks to mitigate emissions of greenhouse gases, particularly CO2.

Statements by dissenting organizations

With the release of the revised statement by the American Association of Petroleum Geologists in 2007, no remaining scientific body of national or international standing is known to reject the basic findings of human influence on recent climate change.

Statements by individual scientists opposing the mainstream assessment of global warming do include claims that the observed warming is likely to be attributable to natural causes.

Scientific consensus

A question which frequently arises in popular discussion of climate change is whether there is a scientific consensus. Several scientific organizations have explicitly used the term "consensus" in their statements:

* American Association for the Advancement of Science, 2006: "The conclusions in this statement reflect the scientific consensus represented by, for example, the Intergovernmental Panel on Climate Change, and the Joint National Academies' statement."
* US National Academy of Science: "In the judgment of most climate scientists, Earth’s warming in recent decades has been caused primarily by human activities that have increased the amount of greenhouse gases in the atmosphere. ... On climate change, the National Academies’ reports have assessed consensus findings on the science..."
* Joint Science Academies' statement, 2005: "We recognise the international scientific consensus of the Intergovernmental Panel on Climate Change (IPCC)."
* Joint Science Academies' statement, 2001: "The work of the Intergovernmental Panel on Climate Change (IPCC) represents the consensus of the international scientific community on climate change science. We recognise IPCC as the world’s most reliable source of information on climate change and its causes, and we endorse its method of achieving this consensus."
* American Meteorological Society, 2003: "The nature of science is such that there is rarely total agreement among scientists. Individual scientific statements and papers—the validity of some of which has yet to be assessed adequately—can be exploited in the policy debate and can leave the impression that the scientific community is sharply divided on issues where there is, in reality, a strong scientific consensus.... IPCC assessment reports are prepared at approximately five-year intervals by a large international group of experts who represent the broad range of expertise and perspectives relevant to the issues. The reports strive to reflect a consensus evaluation of the results of the full body of peer-reviewed research.... They provide an analysis of what is known and not known, the degree of consensus, and some indication of the degree of confidence that can be placed on the various statements and conclusions."
* Network of African Science Academies: “A consensus, based on current evidence, now exists within the global scientific community that human activities are the main source of climate change and that the burning of fossil fuels is largely responsible for driving this change.”

* International Union for Quaternary Research, 2008: "INQUA recognizes the international scientific consensus of the Intergovernmental Panel on Climate Change (IPCC)."
* Australian Coral Reef Society, 2006: "There is almost total consensus among experts that the earth’s climate is changing as a result of the build-up of greenhouse gases.... There is broad scientific consensus that coral reefs are heavily affected by the activities of man and there are significant global influences that can make reefs more vulnerable such as global warming...."

Surveys of scientists and scientific literature

Various surveys have been conducted to determine a scientific consensus on global warming.

Doran and Kendall Zimmerman, 2009

A poll performed by Peter Doran and Maggie Kendall Zimmerman at Earth and Environmental Sciences, University of Illinois at Chicago received replies from 3,146 of the 10,257 polled Earth scientists. Results were analyzed globally and by specialization. 76 out of 79 climatologists who "listed climate science as their area of expertise and who also have published more than 50% of their recent peer-reviewed papers on the subject of climate change" believe that mean global temperatures have risen compared to pre-1800s levels, and 75 out of 77 believe that human activity is a significant factor in changing mean global temperatures. Among all respondents, 90% agreed that temperatures have risen compared to pre-1800 levels, and 82% agreed that humans significantly influence the global temperature. Petroleum geologists and meteorologists were among the biggest doubters, with only 47 percent and 64 percent, respectively, believing in human involvement. A summary from the survey states that:

"It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes."

STATS, 2007

In 2007, Harris Interactive surveyed 489 randomly selected members of either the American Meteorological Society or the American Geophysical Union for the Statistical Assessment Service (STATS) at George Mason University. The survey found 97% agreed that global temperatures have increased during the past 100 years; 84% say they personally believe human-induced warming is occurring, and 74% agree that “currently available scientific evidence” substantiates its occurrence. Only 5% believe that that human activity does not contribute to greenhouse warming; and 84% believe global climate change poses a moderate to very great danger.

Oreskes, 2004

A 2004 article by geologist and historian of science Naomi Oreskes summarized a study of the scientific literature on climate change. The essay concluded that there is a scientific consensus on the reality of anthropogenic climate change. The author analyzed 928 abstracts of papers from refereed scientific journals between 1993 and 2003, listed with the keywords "global climate change". Oreskes divided the abstracts into six categories: explicit endorsement of the consensus position, evaluation of impacts, mitigation proposals, methods, paleoclimate analysis, and rejection of the consensus position. 75% of the abstracts were placed in the first three categories, thus either explicitly or implicitly accepting the consensus view; 25% dealt with methods or paleoclimate, thus taking no position on current anthropogenic climate change; none of the abstracts disagreed with the consensus position, which the author found to be "remarkable". According to the report, "authors evaluating impacts, developing methods, or studying paleoclimatic change might believe that current climate change is natural. However, none of these papers argued that point."

Bray and von Storch, 2003

A survey was conducted in 2003 by Dennis Bray and Hans von Storch. Bray's submission to Science on December 22, 2004 was rejected, but the survey's results were reported through non-scientific venues. The survey received 530 responses from 27 different countries. One of the questions asked was "To what extent do you agree or disagree that climate change is mostly the result of anthropogenic causes?", with a value of 1 indicating strongly agree and a value of 7 indicating strongly disagree. The results showed a mean of 3.62, with 50 responses (9.4%) indicating "strongly agree" and 54 responses (9.7%) indicating "strongly disagree". The same survey indicates a 72% to 20% endorsement of the IPCC reports as accurate, and a 15% to 80% rejection of the thesis that "there is enough uncertainty about the phenomenon of global warming that there is no need for immediate policy decisions."

The survey has been criticized on the grounds that it was performed on the web with no means to verify that the respondents were climate scientists or to prevent multiple submissions. The survey required entry of a username and password, but the username and password were circulated to a climate skeptics mailing list and elsewhere on the internet. Bray and von Storch defended their results and accused climate change skeptics of interpreting the results with bias.

Bray and von Storch distributed an updated version of their survey in August 2008, sent to 1842 selected scientists drawn from authors in ISI listed climate related journals for the past 10 years, as well as lists used in previously published analyses. This survey contains a web link with a unique identifier for each respondent. Results of this survey are not yet available.

Survey of U.S. state climatologists, 1997

In 1997, the conservative think tank Citizens for a Sound Economy surveyed America's 48 state climatologists on questions related to climate change. Of the 36 respondents, 44% considered global warming to be a largely natural phenomenon, compared to 17% who considered warming to be largely man-made. The survey further found that 58% disagreed or somewhat disagreed with then-President Clinton's assertion that "the overwhelming balance of evidence and scientific opinion is that it is no longer a theory, but now fact, that global warming is for real". Eighty-nine percent agreed that "current science is unable to isolate and measure variations in global temperatures caused ONLY by man-made factors," and 61% said that historical data do not indicate "that fluctuations in global temperatures are attributable to human influences such as burning fossil fuels."

Sixty percent of the respondents said that reducing man-made CO2 emissions in the US by 15% below 1990 levels would not prevent global temperatures from rising, and 86% said that reducing emissions in the US to 1990 levels would not prevent rising temperatures. Thirty nine percent agreed and 33% disagreed that "evidence exists to suggest that the earth is headed for another glacial period," though the time scale for the next glacial period was not specified.

Bray and von Storch, 1996

In 1996, Dennis Bray and Hans von Storch undertook a survey of climate scientists on attitudes towards global warming and related matters. The results were subsequently published in the Bulletin of the American Meteorological Society. The paper addressed the views of climate scientists, with a response rate of 40% from a mail survey questionnaire to 1000 scientists in Germany, the USA and Canada. Most of the scientists believed that global warming was occurring and appropriate policy action should be taken, but there was wide disagreement about the likely effects on society and almost all agreed that the predictive ability of currently existing models was limited.

The abstract says:

The international consensus was, however, apparent regarding the utility of the knowledge to date: climate science has provided enough knowledge so that the initiation of abatement measures is warranted. However, consensus also existed regarding the current inability to explicitly specify detrimental effects that might result from climate change. This incompatibility between the state of knowledge and the calls for action suggests that, to some degree at least, scientific advice is a product of both scientific knowledge and normative judgment, suggesting a socioscientific construction of the climate change issue.

The survey was extensive, and asked numerous questions on many aspects of climate science, model formulation, and utility, and science/public/policy interactions. To pick out some of the more vital topics, from the body of the paper:

The resulting questionnaire, consisting of 74 questions, was pre-tested in a German institution and after revisions, distributed to a total of 1,000 scientists in North America and Germany... The number of completed returns was as follows: USA 149, Canada 35, and Germany 228, a response rate of approximately 40%....

...With a value of 1 indicating the highest level of belief that predictions are possible and a value of 7 expressing the least faith in the predictive capabilities of the current state of climate science knowledge, the mean of the entire sample of 4.6 for the ability to make reasonable predictions of inter-annual variability tends to indicate that scientists feel that reasonable prediction is not yet a possibility... mean of 4.8 for reasonable predictions of 10 years... mean of 5.2 for periods of 100 years...

...a response of a value of 1 indicates a strong level of agreement with the statement of certainty that global warming is already underway or will occur without modification to human behavior... the mean response for the entire sample was 3.3 indicating a slight tendency towards the position that global warming has indeed been detected and is underway.... Regarding global warming as being a possible future event, there is a higher expression of confidence as indicated by the mean of 2.6.

Older surveys of scientists

* Global Environmental Change Report, 1990: GECR climate survey shows strong agreement on action, less so on warming. Global Environmental Change Report 2, No. 9, pp. 1-3
* Stewart, T.R., Mumpower, J.L., and Reagan-Cirincione, P. (1992). Scientists' opinions about global climate change: Summary of the results of a survey. NAEP (National Association of Environmental Professionals) Newsletter, 17(2), 6-7.
* In 1991, the Center for Science, Technology, and Media commissioned a Gallup poll of 400 members of the American Geophysical Union and the American Meteorological Society along with an analysis of reporting on global warming by the Center for Media and Public Affairs, a report on which was issued in 1992. Accounts of the results of that survey differ in their interpretation and even in the basic statistical percentages:
o Fairness and Accuracy in Reporting states that the report said that 67% of the scientists said that human-induced global warming was occurring, with 11% disagreeing and the rest undecided.
o George Will reported "53 percent do not believe warming has occurred, and another 30 percent are uncertain." (Washington Post, September 3, 1992). In a correction Gallup stated: "Most scientists involved in research in this area believe that human-induced global warming is occurring now."
o A 1993 publication by the Heartland Institute reports: "A Gallup poll conducted on February 13, 1992 of members of the American Geophysical Union and the American Meteorological Society-the two professional societies whose members are most likely to be involved in climate research-found that 18 percent thought some global warming had occurred, 33 percent said insufficient information existed to tell, and 49 percent believed no warming had taken place."

From http://en.wikipedia.org/