The U.S. Environmental Protection Agency recently issued a landmark proposal to limit carbon dioxide emissions from existing fossil fuel–fired power plants in an effort to combat climate change. Surprisingly, the agency’s analysis of its proposal fails to say how much global warming the proposal would prevent.

Fossil fuel–fired plants that power air conditioning, lighting, laptops, and plug-in vehicles are the biggest source of greenhouse gases in the United States. Regulating emissions from those plants is the best opportunity for the Obama administration to deliver on its promises to combat climate change. Yet the EPA’s analysis of its proposal, which runs 376 pages, provides questionable estimates of the dollar benefits in 2030 of the climate change averted—$30 billion—without estimating the projected change in the global average temperature from the proposal.

The EPA’s benefits estimates rely on the tons of carbon emissions reduced by its proposal and federal estimates of the “social cost of carbon” (SCC). The SCC represents total global damages from all foreseeable future climate change associated with one ton of carbon emissions. This estimate, however, is contentious.

Massachusetts Institute of Technology economist Robert Pindyck wrote in the Fall 2013 Journal of Economic Literature that “models [used to estimate the SCC] have crucial flaws that make them close to useless as tools for policy analysis.” He added that “the models’ descriptions of the impact of climate change are completely ad hoc, with no theoretical or empirical foundation.” He noted that arbitrary assumptions about certain inputs, such as the choice of discount rate, have huge effects on the SCC estimates.

The SCC also relies on an assumption quite rare in government analyses of regulatory policies. It includes benefits to foreigners as well as Americans, while the typical approach focuses only on effects on Americans. The Obama administration elsewhere has estimated that benefits to foreigners could range from 77 to 93 percent of the global climate benefits in the SCC.

The EPA has previously provided quantitative estimates of the various measures of climate change averted by regulation. In a 2012 regulation setting emissions standards for light-duty cars and trucks, the EPA stated that as a result of the emissions reductions from the rule, by 2100 “the global mean temperature is projected to be reduced by approximately 0.007–0.018° C, and global mean sea level rise is projected to be reduced by approximately 0.07–0.16 cm.” The Cato Institute’s Paul Knappenberger and Patrick Michaels estimated that a comparable amount of warming would be averted by the EPA’s proposed utility rule—about 0.018° C in 2100—using a publicly available model developed by academic researchers with support from the EPA and other organizations.

Global issue / The modest and even insignificant size of those projected effects reflects the huge inertia present in the planet’s climate and, more importantly, the limited effect of unilateral U.S. action. Actions by other countries—especially China and India, where emissions are growing—are essential to efforts to reduce global warming. The U.S. Energy Information Agency predicts that virtually all growth in global emissions of carbon related to energy use—the single biggest source of greenhouse gases—will occur in countries that are not industrialized democracies. Under current policies, such countries will account for more than two-thirds of global emissions by 2040, and China and India are responsible for the lion’s share of that emissions growth.

It is unclear how the EPA’s action may affect efforts by other countries to limit emissions. On Nov. 11th, President Xi of China and President Obama jointly announced new emissions targets:

The United States intends to achieve an economy-wide target of reducing its carbon emissions 26%–28% below its 2005 level in 2025 and to make best efforts to reduce its emissions by 28%. China intends to achieve the peaking of [carbon dioxide] emissions around 2030 and to make best efforts to peak early and intends to increase the share of non–fossil fuels in primary energy consumption to around 20% by 2030.

The idea that Chinese carbon emissions will peak around 2030 is not new. Researchers affiliated with the Lawrence Berkeley National Laboratory made projections of peaks by 2030 in 2013. Further, the shift in electricity generation toward non–fossil fuels is driven by China’s concern with extreme local air pollution. China’s announcement thus does not appear to represent much change relative to recent forecasts. But it is new that the Chinese president has endorsed such a peak as a goal, even if—as our Resources for the Future colleague Nathan Richardson has noted—the endorsement does not legally bind anyone now or in the future.

India, whose emissions are the fourth largest in the world and growing at 5 percent annually, seems unlikely to adopt greenhouse gas controls as a result of the EPA rulemakings. At the September United Nations climate summit, India was not represented by its prime minister, but by its environment minister, Prakash Javadekar, who said, “India remains committed to pursuing a path of sustainable development through eradication of poverty, both of income as well as energy.”

The EPA is issuing greenhouse gas regulations partly because Congress has not been able to agree on what to do to control U.S. emissions that increase risks to the global ecosystem. An administrative agency acting without express congressional authorization ought to meet the highest standards of accountability and transparency when analyzing policy proposals. The power plant emissions proposal analysis fails to meet those standards.

The EPA should immediately report, as it has previously done, how much global warming its new proposed rule would avert by specific dates, such as 2100. Such information is essential to giving Congress and the public the full information they need to see and navigate the long, hot road ahead.