EDIT
For a 50:50 chance of keeping a global temperature rise within 2 °C by 2100, we must halve emissions by 2050. This is the message of climate models by Keywan Riahi of the International Institute for Applied Systems Analysis in Laxenburg, Austria, and colleagues. That means 70 per cent of global energy production must be zero-emissions by 2050.
To see if that target was realistic, the team used factors such as the average rate of technology diffusion in the past. Our prospects are poor even if we roll out sources like wind and nuclear power as fast as we can, plus any new ones that become available before 2050.
"We have only a slim chance," says Mark New at the Tyndall Centre for Climate Change Research in Norwich, UK. "It looks like we'll have to prepare for warming greater than 2 °C or hope that geoengineering will get us out of trouble."
EDIT/END
http://www.newscientist.com/article/dn18374-avoiding-dangerous-warming-by-2100-barely-feasible.html?DCMP=OTC-rss&nsref=climate-change