The so-called social cost of carbon is a mathematical evaluation of how much the emission of 1 ton of carbon dioxide is likely to cost society through future climate change — given damages to infrastructure, agriculture, human health, and otherwise. It's a little-known value in the public sphere, but one that contains tremendous potential to influence the cost-benefit analyses that help shape environmental policy, and it's long been the subject of controversy.
In its proposed repeal of U.S. EPA's Clean Power Plan — a 2015 rule to limit power plants' greenhouse gas emissions — the Trump team included a lengthy report that dramatically altered the costs projected by the last administration.
The Obama administration pegged the social cost of carbon at about $42 per ton by 2020. But the new EPA document significantly lowers that estimate, placing it between $1 and $6 per ton.
More broadly, that number crunching suggests that Trump's aides will place a much lower emphasis on the costs of climate change in future rule makings across government; the administration is in the process of reconsidering a swath of President Obama's climate regulations at EPA and other agencies. It comes after some federal courts have chided agencies for failing to adequately consider the climate impacts of fossil fuel projects. Some have also noted that although Trump has previously called climate change a "hoax," his administration did account for costs of climate change in its draft rule.
Obama's social cost of carbon was an early target for the Trump team. In the same March executive order in which Trump directed EPA to review the Clean Power Plan, he also revoked Obama's social cost of carbon calculation.
Some of Trump's supporters, including advocates of the oil and gas industry, have long criticized the use of the social cost of carbon in environmental regulations or suggested that its value is too high. Indeed, higher values of the social cost of carbon suggest greater damage caused by carbon emissions, which generally justifies more stringent regulation of the fossil fuel industry.
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Some experts feel EPA has failed to provide adequate scientific rationale for its revised estimates.
Michael Greenstone, an economist at the University of Chicago and former chief economist for Obama's Council of Economic Advisers, suggested in an interview with E&E News that the methods behind the revised estimates constituted little more than "just an effort to find the dials that you could turn to bring the number down." Greenstone helped convene the first federal working group to begin assessing the social cost of carbon in 2009.
"This was not evidence-based policymaking, this was policy-based evidence-making," he said. "What that means is the policy gets set, and then you have to go backwards and create the evidence to support it."
Meanwhile, a new report from the Government Accountability Office released this week is urging the Trump administration to seriously consider the economic risks of climate change and develop the appropriate federal responses. While research on these risks is still emerging, it notes, studies suggest that extreme weather events have already cost the federal government hundreds of billions of dollars over the last decade, and the costs will likely rise as the planet continues to heat up.
Trump 'entitled to disagree'
The social cost of carbon relies on a series of complex calculations involving models, which help predict the damages likely to be incurred by future climate change, and an economic principle known as a "discount rate," a kind of interest rate that helps address the idea of how much society is willing to pay now to avoid damages in the future. Changes to any of the steps involved in the calculations can result in drastically different values.
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A National Academy of Sciences report released earlier this year on the calculation of the social cost of carbon included a number of recommendations for updating the methods used in the calculations to make them more scientifically sound.
But the new administration's revised calculations involve methods that largely ignore those recommendations, according to Richard Newell, co-chair of the committee that released that report and president and CEO of think tank Resources for the Future.
For one thing, the lowest value presented in EPA's report relies on the use of a higher discount rate than was applied in the Obama-era calculations. In simple terms, a higher discount rate results in a lower social cost of carbon and vice versa, and there's been considerable debate about what rate is appropriate. The previous estimate of $42 relied on a rate of 3 percent, while the revised calculations' lower estimate of $1 uses a rate of 7 percent, which some experts say is too high.
"There are good reasons to think that such a high discount rate is inappropriate for use in estimating the SCC," Newell wrote in a blog post.
And EPA's report also considers only the domestic social cost of carbon, rather than its cost at a global scale, as has been the focus previously — a highly controversial shift that requires deep consideration of "our values as a society," according to Frances Moore, a professor of environmental science and policy at the University of California, Davis, who has conducted research on the social cost of carbon.
"By using a domestic number, what essentially we're saying in our evaluation of climate policy is that the U.S. does not care about impacts happening to people not in the United States," she noted.
The Trump EPA said it was following guidelines from the White House budget office and the president that domestic — and not global — damages be calculated.
Other experts have taken issue with what they feel is a lack of justification, scientific or otherwise, from the federal government for making this shift in the first place.
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Some argue Obama underestimated climate costs
Values aside, some scientists have previously pointed out that climate impacts in other parts of the world have the potential to trickle back to the United States. Damage to agriculture in one nation, for instance, could affect consumers downstream in other parts of the world.
But even if that were not the case, Moore suggests that the models used to evaluate the climate impacts in the United States — or anywhere for that matter — may not be entirely up to date. In fact, some researchers believe that the current models significantly underestimate the economic impacts of future climate change and that even the Obama-era estimates were far too low.
Moore has published research that suggests the models don't accurately account for the impact of higher temperatures on gross domestic product and that correcting for this issue could result in a social cost of carbon approximately six times higher than previous estimates have reflected. She's conducting similar research on the economic impacts of climate change on agriculture, which could be similarly underestimated.
Read more at Trump Team's Wonky CO2 Calculation Is a Big Deal
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