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Monday, October 24, 2011

Joeri Rogelj et al., Nature Climate Science: Temperature targets slipping away

Temperature targets slipping away

by Genelle Weule, ABC, October 24, 2011

The international community will not meet agreed temperature targets unless it puts the brakes on current levels of carbon emissions now, warn climate scientists.
The team of scientists led by Dr Joeri Rogelj from the Institute for Atmospheric and Climate Science in Zurich, analysed emission scenarios to identify the likelihood of limiting global temperature rises to 2 °C above pre-industrial levels.

Their analysis, published online in today's Nature Climate Science, shows global median CO2 equivalent emissions need to peak and fall to 44 gigatonnes by 2020 to have a likely chance of meeting targets set in Cancun.

"At the moment we are about 48 gigatonnes [of CO2 equivalent] so we are at higher levels globally," says study co-author Dr Malte Meinshausen, a German climate scientist currently based at the University of Melbourne.

To maintain the two-degree limit beyond 2020, emissions would need to fall to a median of 20 gigatonnes by 2050, Meinshausen says.

"That means global emissions have to peak within this decade and then have to go down again. At the moment, although the world recognises the climate problem, we are producing more and more emissions every year and accelerating the problem."

Optimal trajectory

The researchers assessed the economic and technical feasibility of 193 emissions pathways from the scientific literature and predicted whether these scenarios would be very likely, likely or have a 50:50 chance of meeting the 2 °C temperature target.

"These pathways look at what is the optimal trajectory in economic terms to reach a certain climate target like 2 °C or 450 ppm CO2."

"What we get out of these pathways is a smooth trajectory that will realistically with our current knowledge allow us to say there are economically [and] technically feasible pathways to reduce emissions back to very low levels," says Meinshausen.

But he says the study shows pledges made from the international community are "insufficient to move the world onto a 2 °C trajectory."

"This analysis shows us if you want to have a more optimal pathway without betting on very dramatic emission reductions after 2020, then by 2020 you should aim for the milestone of 44 gigatonnes of CO2 [equivalent]," says Meinshausen.

Higher 2020 emissions and later peaking as a result of weaker early mitigation action would reduce the chances of staying below the 2 °C target, say the researchers.

"It is not that the 2 °C target has slipped out of reach already, but if there is 10 years more of inaction, if there is 10 years of following only low ambition pathways, then we are very close to the point where we don't know that there are technologies that would be able reduce the emissions fast enough to be able to reach the two-degree pathway," says Meinshausen. "So we are very close to the cliff."

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