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Rate of Greenland ice sheet melt

A climate tipping point is a somewhat ill-defined concept of 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.

Global warming proceeds by changing the composition of gases in the Earth's atmosphere and Oceans by the emission of greenhouse gases such as carbon dioxide and methane. 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 and/or West Antarctic Ice Sheet. At some level of temperature rise, the melt of the entire ice sheet will become inevitable; but the ice sheet itself may persist for millennia[citation needed]. A tipping point may be passed without any immediately obvious consequences, nor any acceleration of the warming process. Carbon dioxide as of May 2012 makes up 396.18 ppm of Earth's atmosphere[1] and monitoring stations in the Arctic spring 2012 measuring more than 400 ppm of the heat-trapping gas in the atmosphere.[2] James E. Hansen said that this tipping point had already been reached in April 2008 when the CO
2 level was 385 ppm. (Hansen states 350 ppm as the upper limit.) "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."[3] He has further suggested potential projections of runaway climate change on Earth creating more Venus-like conditions in his book Storms of My Grandchildren.

Scientists and other specialists continue to express concern about global warming and irreversible tipping points. They have used metaphors such as "the door is closing"[4] and warned of global food[citation needed] and water shortages[citation needed], hundreds of millions of people being displaced by rising sea levels, famine, unhealthy and unlivable conditions, and storms becoming ever more frequent and severe worldwide.[5]

Others have tried systematically to short-list large scale components of the Earth system that may be subject to tipping points, defining tipping points as a variety of phenomena, including the onset of positive feedback, hysteresis effects, and the possible effect of statistical noise at critical points.[6]

Examples


The climate change in the Arctic image above shows where average air temperatures (October 2010-September 2011) were up to 3 degrees Celsius above (red) or below (blue) the long-term average (1981-2010).

Lenton et al. highlights a number of tipping elements, including:[6]