Warming in danger zone

Humans have already released half the total carbon dioxide emissions permissible before the planet is at risk of warming to dangerous levels, a draft United Nations scientific assessment says.

The final draft of a major assessment by the Intergovernmental Panel on Climate Change suggests that keeping warming to 2 degrees - regarded as a guard-rail against the worst impacts of climate change - will require deep global emissions cuts in coming decades.

Under the future emissions scenarios considered by the IPCC, only the most stringent would keep the world within the remaining CO2 allowance for 2 degrees. It would mean an average global emission cut of 50 per cent by mid-century on 1990 levels, and possibly require removal of carbon dioxide from the atmosphere by 2100.

The draft report lifts the IPCC's scientific certainty that human activity - such as burning fossil fuels - caused more than half the warming since the middle of last century to a 95 per cent confidence.

For the first time, the IPCC draft also includes an estimate of the total cumulative CO2 emissions that can be released since pre-industrial times to give the world above a 66 per cent chance of keeping warming below 2 degrees.

The draft estimates total human CO2 emissions need to be limited to about 3670 billion tonnes of carbon dioxide to keep below 2 degrees. If the world proceeds along the highest future emissions path, a further 6183 billion tonnes of CO2 would be released by 2100, the draft says, meaning potential temperature rises of 2.6 to 4.8 degrees by century's end.

 

http://www.smh.com.au/environment/climate-change/warming-in-danger-zone-20130920-2u5jx.html