News•December 21, 2012

It’s Not Too Late to Limit Global Temperatures - But Almost

For a couple of years now, climate scientists have agreed that to avoid the most serious consequences of global warming we need to cap the planet’s average temperature at no more than 2 degrees C (or 3.6°F) above where it stood in the 1800s. The temperature has already risen by about 1°C—the longer we wait to rein in greenhouse-gas emissions, the harder it will be to reach that goal — and the recent international climate talks in Doha made it clear that emissions aren’t likely to be reined in anytime soon.

This raises the question of how much more those emissions could grow before the 2°C target becomes physically impossible to achieve. And a recent paper in Nature Climate Change has a somewhat encouraging answer. Even if annual emissions nearly double by 2020 from today’s 30 billion tons or so, it would still be possible to cap the temperature rise at 2°C, or at worst, rise slightly above that level before coming back down.

Emissions from portable asphalt plant in Wisconsin.
Credit: flickr/Wisconsin Department of Natural Resources

That’s the good news. The bad news is that “possible” doesn’t mean “easy,” by a long shot. Capping temperatures after such a large increase in emissions would be “technically feasible,” co-author Brian O’Neill said in an interview, “but so many things would have to go right that you’d have to be a very optimistic person to bet that it would actually happen.”

O’Neill said the problem is that emissions would have to be cut quickly and drastically after 2020. The technology for doing so already exists, including nuclear power, biofuels and the capture and storage of carbon from power-plant smokestacks before it can enter the atmosphere.

“It would have to be feasible to scale all of them up globally, and they couldn’t be prohibitively expensive,” he said. “You’d have to retire most of the world’s coal-burning plants, and countries would have to work together to make it all happen.”

The good news, say the study’s authors, is that emissions needn’t double by 2020, especially if energy-hungry nations put some effort into improving the efficiency of cars, buildings, factories and other energy hogs.

Coal fired power plant’s smokestack emissions.
Credit:flickr/Emilian Robert Vicol

“If we did nothing other than reduce energy demand through efficiency and lifestyle changes before 2020,” O’Neill said, “we could meet the 2°C target even if we didn’t build more nukes, or if we put limits on the amount of land devoted to biofuels” — two options that would otherwise be impossible.

Still, without some strong new agreements on emissions, meeting the 2°C target is likely to be a tall order given that nations would have to work together.

“Politics is a separate question,” O’Neill said, noting that the 2°C number is an international target that many countries have publicly agreed to in principle. “Whether they’re serious about it or not, we’re not judging.”

But this kind of study can still be useful. “It can inform what’s technically and economically feasible,” O’Neill said. “People need to understand implications of the temperature targets they’re agreeing to. I’m not sure they always do.”