By Sid Perkins
To prevent Earth’s average temperature from rising more than 2 degrees Celsius above preindustrial levels, several teams of researchers suggest that policymakers limit cumulative carbon emissions to no more than 1 trillion metric tons.
The researchers suggested the goal and a possible road map during an April 27 teleconference and in the April 30 Nature. The task is daunting because human activity has already exhausted more than half that allotment since the Industrial Revolution began. Human activity will likely emit the rest of that budget in just a few decades, even if emissions are held at the current rate.
The two-degree limit comes from the most recent report by the Intergovernmental Panel on Climate Change as a way to reduce the risks of severe impacts from a warming climate.
The recent studies may be the first to suggest a limit on the total amount of anthropogenic carbon and therefore carbon dioxide emissions, rather than a particular atmospheric concentration of the greenhouse gas. Establishing a ceiling for human emissions of carbon dioxide “actually makes the problem simpler than it’s often portrayed … because it treats emissions as an exhaustible resource,” says David Frame, an atmospheric scientist at the University of Oxford and a coauthor of the Nature papers. “If you burn a ton of carbon today, then you can’t burn it tomorrow.”