Tipping point (climatology)

A climate tipping point is a point when global climate changes from one stable state to another stable state, in a similar manner to a wine glass tipping over. After the tipping point has been passed, a transition to a new state occurs. The tipping event may be irreversible, comparable to wine spilling from the glass - standing up the glass will not put the wine back. As regards climate, Geoengineering may be proposed or used to prevent or reverse a tipping point event.

Global warming proceeds by changing the composition of gases in the Earth's atmosphere by the emission of greenhouse gases such as carbon dioxide and methane. Remedial action to restrain the rate of change may be proposed by reducing greenhouse gas emissions to slow down and stop and eventually reduce their build up.

As warming proceeds it brings about changes to the natural environment which may result in other changes. For example, warming may begin to melt the Greenland ice sheet. At some level of temperature rise, the melt of the entire ice sheet will become inevitable, even though complete melting may not occur for millennia. Thus a "tipping point" may be passed without any immediately obvious consequences. Nor does the use of tipping point imply any acceleration of the warming process.

Some eminent scientists, notably James Hansen, NASA's top climate scientist believe this point has already been reached with carbon dioxide levels currently at 385 ppm.

"Further global warming of 1 °C defines a critical threshold. Beyond that we will likely see changes that make Earth a different planet than the one we know." Jim Hansen, director of NASA's Goddard Institute for Space Studies in New York.

Other scientists maintain the term is too vague for a non-linear system such as the Earth's climate where they may be a number of states where conditions may flip and go rapidly into another state and other conditions which may return it to equilibrium. It has been suggested the phrase is more a political slogan to rally support for action to mitigate greenhouse gas emissions.

Examples

Lenton et al. highlights a number of tipping points including

* Boreal forest dieback
* Amazon rainforest dieback
* ENSO
* Loss of Arctic and Antarctic sea ice and melting of Greenland and Antarctic ice sheets
* Ozone hole
* Disruption to Indian and West African monsoon
* Formation of Atlantic deep water near the Arctic ocean, which is a component process of the thermohaline circulation.
* Loss of permafrost, leading to potential Arctic methane release and Clathrate gun effect

From http://en.wikipedia.org/