two degrees apart

The world can still prevent dangerous global warming if it acts fast / Michael A. Mann

The article was published with the approval of Scientific American Israel and the Ort Israel network

The world will have a very hard time preventing its surface temperatures from rising by more than 2 degrees Celsius: the threshold above which the planet will be hit hard. This number is behind the commitments that many countries will make at the UN Climate Conference (COP21) held in early December 2015 in Paris in order to reduce their greenhouse gas emissions.

However, some argue that this "goal of two virtues" is impossible. They say that it is impossible to install and operate the technologies necessary to reduce economic dependence on carbon in the near future. But it is possible. The difficulty is not physical but a matter of political and public willpower.

No one claims that this will be easy. More than 70 climate experts, who advised the United Nations Framework Convention on Climate Change, said that limiting global warming to 2 degrees "requires radical change ... and not just fine-tuning of current trends."

We can only emit another 270 billion tons of carbon into the atmosphere before warming leads to an increase of 2 degrees. At the current rate of emissions, which is more than 10 billion tons per year, we will burn this "carbon allowance" in only thirty years. According to one recent analysis, to stay below the 2 degree limit we will have to leave in the ground a third of the proven oil reserves, half of all the natural gas reserves and 80% of the coal reserves.

This is therefore a huge demand. This means that we must begin immediately to say goodbye to coal mining and we must abandon most, if not all, of Canada's tar sands (goodbye to the Keystone XL pipeline). It also means that we cannot burn increasing amounts of natural gas as a "bridge" to a cleaner climate future achieved by renewable energy sources.

The parallel is often drawn between the 2 degree threshold and maintaining the concentration of carbon dioxide in the atmosphere below 450 parts per million. This challenge is harder to meet as coal use declines. When coal is burned, it releases sulfuric aerosol particles into the atmosphere, and these return some of the sun's energy to space. For an article I wrote in Scientific American in 2014 called "False Hope", I calculated and found that in order to offset the complete cessation of sulfur emissions we would have to meet a CO2 concentration target of 405 parts per million, but slightly higher than today's concentration.

Do we have a chance to succeed? Climate scientist James A. Hansen has shown convincingly that we can remove 100 billion tons of carbon from the air by extensive forests. Such reforestation is possible by restricting land use to the extent that allows forests to grow and cover again the areas they covered before humans started cutting them down. Such afforestation and the reduction of carbon emissions by a few percent per year, a difficult but possible task, will allow us to meet the goal of stabilization below 2 degrees.

History is full of early declarations of impossibility that prevented action and later turned out to be wrong. As Joe Rome of the American Center for Progress said in response to the climate skeptics: "Thank God these scholars weren't around when we had to do something really hard, like take literally thousands of lives and rebuild our entire economy almost overnight to win World War II." " An inspiring agreement at the COP21 climate summit in Paris in December could set in motion an ambitious but certainly doable move.

The key is that there are technological developments and cost reductions due to the large volumes, which are only revealed when the actual implementation begins. The price of solar cells in the world, for example, has fallen by more than 50% in recent years as China increased their production. Those who say "it is impossible" are building a self-fulfilling prophecy. The United States has never been a nation of "can'ts".

Even with innovations and increased scope, it is possible that at some point we will have to use the technology of "direct capture from the air" to absorb carbon dioxide from the atmosphere. It would be expensive, but Klaus Leckner, an engineering professor at the University of Arizona, is confident that the cost could be brought down to $30 per ton by mass production.

The price of the action is only half the price of avoiding it. This is not the conclusion of the Intergovernmental Panel on Climate Change (IPCC), but of the oil company ExxonMobil, which found that the true cost to society of carbon emissions is $60 per ton. And there are higher estimates than that. Can we afford to stabilize global warming below 2 degrees Celsius? We cannot afford not to.

About the writers

Michael A. Mann
Research Professor of Meteorology at the University of Pennsylvania. His latest book, co-authored with Lee R. Kemp, is "Bitter Predictions: Understanding Climate Change"