The United States would suffer the largest costs of climate change

Climate change is a classic tragedy of the commons: each country acting in its own interest contributes to the depletion of a common resource, thus worsening the world for all. If you have ever lived with bad roommates, the concept will be easy to understand. The social cost of carbon (or CCS) is a way to quantify the outcome of this tragedy, quantifying how much climate change will cost the world in generations to come.

But a paper in Nature Climate Change this week is trying to bring costs closer to home by estimating what CSC could be for each country. These new calculations indicate a wide range of different cost opportunities, but with some consistent messages: the cost will likely be higher than previous estimates; the United States will be one of the most affected countries; and many of the countries that contribute the least to the problem will be criticized anyway.

Transparency, uncertainty and rigor

The concept of SCC has existed for a long time, with many different ways of calculating it. Since it is impossible to know with certainty what the future holds, these estimates lead to quite different results according to the hypotheses they have formulated. For example, it is impossible to know for sure what economic growth will be, and such different assumptions will lead to different estimates of CCS.

This type of uncertainty has led to a recent report from the National Academy of Sciences recommending three important qualities that SCC estimates should prioritize. Estimates must be transparent, making it easy to see the assumptions used in the calculations. they must scrupulously explain where the uncertainties are and what is the range of estimates; and they should focus on basing their estimates on high quality scientific data.

Katharine Ricke and her colleagues took this advice seriously, providing a new estimate with open material so that others could delve into the weeds and check their work. They focused on making their estimate based on the best available data and how uncertainty about the future affects the results.

These uncertainties are omnipresent. There is the uncertainty of the carbon emissions themselves, how the climate will react exactly and what the damage of this reaction will be. There are schools of thought on the weight of the interests of future citizens compared to ours. And there is no way to know exactly what exactly the population growth and GDP will look like.

Uncertain costs, but robust rankings

Ricke and his colleagues relied heavily on empirical data for their calculations. They use updated climate data, as well as recent estimates of the impact of rainfall and temperature on the GDP growth rate. Their range of uncertainty was wide: for global CSC, the range ranged from around the previous estimates to around USD 40 per tonne of CO₂up to $ 5,000, with some estimates as high as $ 10,000. The average estimate of the global CSC was US $ 417, about 10 times the recent estimates of the Environmental Protection Agency.

The results suggest that India is the country likely to bear the highest cost per tonne of CO₂at an average estimate of US $ 86. The United States occupies second place with $ 48, followed by Saudi Arabia, Brazil and China. The estimates themselves are uncertain, but the rankings, write the authors, are not: they remain almost identical, regardless of where you look.

The costs per country are largely unfair: the countries that contribute the least to global carbon emissions are likely to pay some of the higher costs. India, for example, is expected to pay about four times its fair share of costs in relation to its emissions. China, on the other hand, is the exact opposite. Cold Nordic countries like Canada and Russia even have estimates suggesting that they could reap a net benefit from a warmer climate, although this does not take into account other ways that climate change can transform their economy, as the evolution of international business models.

It's far from being the last word, as Ricke and his colleagues themselves write: "More research is needed to estimate the geographic diversity of climate change impacts and not to incite all countries to clean up their law, although other considerations exist, of course. Regardless of the uncertainties in what the model fact Many factors have not even been taken into account, such as sea level rise and changing patterns of migration.

But for the United States, India, China and others, these numbers create a new way to understand their incentives to act on climate change. "Some of the biggest emitters in the world," write Ricke and his colleagues, "also have a lot to lose from their effects."

Nature Climate Change, 2018. DOI: 10.1038 / s41558-018-0282-y (About the DOIs).