The air pollution over downtown Los Angeles on Sept. 20, 2006. (Gabriel Bouys/Agence France-Presse/Getty Images)

A sweeping Obama-era climate rule could prevent up to 4,500 premature deaths per year by 2030, the Trump administration has found in its analysis of the plan, projecting that the plan could save more lives than the Obama administration said it would.

The Trump administration’s Environmental Protection Agency is moving to repeal the plan.

The rule in question is the Clean Power Plan, which consists of regulations on U.S. power plants aimed at decreasing the country’s contribution to global climate change by reducing its greenhouse gas emissions. In practice, the rule is projected to move the energy sector away from coal-fired power plants and toward more natural gas-fired power plants, as well as wind and solar power sources.

Such power sources have lower emissions of greenhouse gases, but they also produce lower quantities of other pollutants, such as sulfur dioxide. Such pollutants can cause respiratory problems, heart disease and lung cancer, conditions that would therefore be made less prevalent by the climate regulations.

The Obama administration loudly touted the Clean Power Plan’s health benefits while the EPA put measure in place in 2015. At the time, President Barack Obama’s EPA asserted that the plan could prevent 1,500 to 3,600 premature deaths annually by 2030.

But when President Trump’s EPA released a draft analysis of its repeal of the plan last month, it said that in one scenario, the plan would prevent 1,900 to 4,500 premature deaths per year by 2030.

That scenario is based on a 2017 “annual energy outlook” by the federal Energy Information Administration — which contained projections for the evolution of the U.S. power sector with, and without, the Clean Power Plan. It’s a more recent analysis than the ones EPA used under the Obama administration.

“The right way to do this is update your model, your analysis for more recent conditions,” said Alan Krupnick, an economist with the think tank Resources for the Future. “Which is what that second analysis does. And then the chips fall where they may.”

The new figure appears deep in a long, technocratic document called a Regulatory Impact Analysis (RIA) that the EPA released last month when it moved to repeal the plan.

The Trump administration’s EPA has said that, in its analysis of the Clean Power Plan, it has deliberately provided a range of different numbers to outline different possibilities. The agency suggests that this is necessary because there were “numerous concerns and uncertainties associated with the previous administration’s approach.”

“In keeping with Administrator [Scott] Pruitt’s commitment to a heightened level of transparency, the Agency provided a vast series of scenarios of the potential effects of the proposed rule, including those based on EIA’s 2017 Energy Outlook; and we welcome any public comments on the RIA,” said Michael Abboud, an agency spokesman.

From the perspective of the Trump administration’s EPA, the Clean Power Plan was illegally drawn, going beyond the agency’s authority, specifically because it sought to change the broad nature of the energy system, rather than to reduce pollution levels at individual plants. How many lives the policy would save is not central to this legal determination and presumably would not change the agency’s decision to repeal it.

Still, some advocates who support the plan are touting the revision. “The benefits of the Clean Power Plan are even greater than EPA forecast two years ago,” said Paul Billings, the senior vice president for advocacy at the American Lung Association.

The draft Regulatory Impact Analysis provides a formal accounting of the costs and benefits of the EPA’s decision to withdraw from the rule to cut greenhouse gas emissions. It is open for public comment until December 15.

It remains to be seen how the agency ultimately decides to treat the health benefits of addressing climate change in its final analysis — given that, after all, it wants to withdraw the Clean Power Plan. Kathy Fallon Lambert, a researcher at the Harvard Forest, said she worries that there’s a possibility that the agency will ultimately opt to dismiss these “co-benefits” entirely.

When the regulatory analysis document first emerged, it was instantly controversial — the agency had tweaked a variety of tools used to calculate the benefits and costs of environmental actions like this one, shrinking the “social cost of carbon,” changing the assumptions used to determine the present value of actions to aid future generations, and more. Critics quickly denounced the seemingly selective math used to justify a foregone conclusion.

Since then, though, experts poring over the document have found additional details, including one that makes the Clean Power Plan appear considerably better than before. This would indeed appear to bolster the EPA’s contention that it is simply running the numbers and presenting them transparently.

The new data underscore that although the battle over the Clean Power Plan has been cast as one about how the United States does, or doesn’t, address climate pollution emanating from coal plants and other electricity generating stations, the “co-benefits” of reducing air pollution in some ways loom even larger.

After all, even if the United States cuts its greenhouse gas emissions, the entire world would need to do the same to affect the trajectory of climate change in a large way. But air pollution unleashes deadly, tiny particles called PM2.5 that can get into the lungs and bloodstream and cause dangerous outcomes. We’re in fact still learning how bad it really is.

In 2015, the Obama EPA had estimated that sulfur dioxide emissions – which the agency calls a “major precursor” to levels of fine particulate matter, or PM2.5 — would have been as much as 318,000 tons lower in 2030 under the plan than they would have been without it.

Those reductions translated, under one approach to the plan’s implementation, into the avoidance of about 1,500 to 3,600 premature deaths from air pollution each year and $14 to $34 billion in annual benefits in 2030, the agency calculated, most of which were attributable to reductions in sulfur dioxide emissions and resulting fine particles in the air. (Another implementation approach yielded somewhat smaller numbers – 280,000 tons of avoided sulfur dioxide emissions, about 1,300 to 2,900 avoided deaths annually, and $12 to $ 28billion annual benefits in 2030.)

But in the new Trump administration document, the air pollution benefits now appear even better in one version of the analysis. In that scenario, the plan would avoid as much as 423,000 tons of sulfur dioxide emissions in 2030, which translates into the avoidance of an even larger number of premature deaths (as many as 1,900 to 4,500 per year in 2030) and even greater potential benefits, $18 billion to $42 billion.

“The difference is approximately 400-900 deaths per year, or around $4-8 billion each year in health costs,” said Jonathan Levy, a professor at the Boston University School of Public Health, in an emailed comment on the differences in the two analyses. “This is a non-trivial amount of money, not to mention the importance of the public health toll.”

The change, according to an analysis by Dallas Burtraw of Resources for the Future, appears to be because the Energy Information Administration in 2017 estimated that the Clean Power Plan would have an even sharper effect in reducing emissions from the burning of coal than previously predicted — which would mean an even larger effect on air pollution.

It’s important to underscore that all of the numbers presented above are based on different sets of assumptions, many of which can be individually questioned. In essence, they are scenarios, where if you assume a certain set of developments then you can predict an outcome based on those assumptions. But whether the developments will actually happen in the real world is another matter.

The agency also cautions against comparing its 2015 estimates with those made on the basis of the 2017 Energy Information Administration analysis — but that appears to involve how the agency treated the subject of changes in power plant energy efficiency, not air pollution.

“My interpretation is that this would influence costs and net benefits but would not influence the health benefits calculation,” Levy said.

The current data exemplify the connection between climate policy and conventional, non-climate air pollutants, whose concentrations on a local level can be a matter of life and death.

And although critics have harshly criticized the EPA for tweaking its numbers, in this respect at least, it found a result that complicated its argument that the rule should be repealed.

“It’s down in the weeds, but I think it does point to a big picture story that’s important,” Lambert said. “Which is, will these kinds of benefits and emissions reductions occur absent the Clean Power Plan?”

Read more at Energy & Environment:

Trump administration will propose repealing Obama’s key effort to combat climate change

New EPA document reveals sharply lower estimate of the cost of climate change

In unprecedented move, EPA to block scientists who get agency funding from serving as advisers

For more, you can sign up for our weekly newsletter here, and follow us on Twitter here.