About three-quarters of the world's fossil fuel reserves must be left unused if society is to avoid dangerous climate change, scientists warn.
More than 100 nations support the goal of keeping temperature rise below 2C.
But the scientists say that without major curbs on fossil fuel use, 2C will probably be reached by 2050.
Writing in Nature, they say politicians should focus on limiting humanity's total output of CO2 rather than setting a "safe" level for annual emissions.
The UN climate process focuses on stabilising annual emissions at a level that would avoid major climate impacts.
But this group of scientists says that the cumulative total provides a better measure of the likely temperature rise, and may present an easier target for policymakers.
"To avoid dangerous climate change, we will have to limit the total amount of carbon we inject into the atmosphere, not just the emission rate in any given ...