President Donald Trump's aggressive rollback of the Obama administration's climate policies is already changing the trajectory of the world's efforts on global warming, with some analysts estimating it will mean billions more tons of greenhouse gases entering the atmosphere during the next decade and a half.

It could be one of the most durable legacies of his young presidency — regardless of whether Trump decides to withdraw the U.S. from the Paris climate agreement.


Trump has spent much of his first 100 days in office launching a series of efforts to undo former President Barack Obama’s domestic climate policies, seeking to ease pollution limits on power plants, vehicle tailpipes, coal mining, and oil and gas wells. And while Democrats and environmental groups promise fierce resistance, analysts say Trump’s efforts could bring an effective halt to U.S. efforts to cut the carbon pollution that scientists blame for warming the planet.

"This is an experiment we can only run once, and then it’s too late," said Princeton University climate scientist Michael Oppenheimer. "We were in a lot of trouble with climate change already. This only makes it more risky. It's hard to quantify how much it matters, but it makes attainment of a difficult-to-achieve target more or less impossible."

The United States is the world’s second-largest carbon polluter, but its greenhouse gas output has slid sharply in the past decade — a trend driven partly by increases in energy efficiency and a shift from coal to natural gas as a power source. Obama had pledged to continue those reductions in the coming decade to meet U.S. commitments in the 2015 Paris agreement, in which nearly 200 nations made non binding promises to cut their carbon pollution. Hillary Clinton had promised even steeper reductions.

Trump, in contrast, has vowed to reverse Obama’s policies, lift restrictions on the energy industry and “save our wonderful coal miners” — pledges that helped him win fossil fuel-producing swing states like Pennsylvania and Ohio.

And his actions will have a real-world effect, based on POLITICO's analysis of estimates from the Democratic-leaning consultant Rhodium Group and the World Resources Institute. Instead of falling, Rhodium's projection estimated that Trump’s policies, if fully implemented, will cause U.S. carbon pollution to continue more or less at current levels. That means that by 2025, according to POLITICO's analysis, the U.S. would be pumping 900 more megatons of greenhouse gases into the atmosphere each year than under Obama's most ambitious target.

That extra U.S. carbon would exceed the annual output of Germany, one of the world’s top greenhouse gas polluters. That would be enough to increase the world’s annual carbon emissions by almost 2 percent, Pennsylvania State University climate scientist Michael Mann said — at a time when climate researchers say the world urgently needs to accelerate its cuts.

Through 2030, the cumulative gap between the Trump and Obama policies could exceed 4 billion metric tons of carbon dioxide, based on Rhodium's estimates.

In other words, Trump’s domestic actions on energy would be his real contribution to global climate policy — a fact obscured by the noisy political fight on whether the U.S. should withdraw from Paris. The figures don’t even account for the possibility that a U.S. retreat on climate efforts would cause other major polluters, such as China and India, to pull back on their commitments.

"If you’re going after the Clean Power Plan and going after everything else and all the other rules, then whether or not you stay in Paris appears to be symbolic from the perspective of U.S. emissions," said Andrew Light, a fellow at the World Resources Institute who worked for the State Department under Obama.

Rhodium based its analysis on a March 28 executive order in which Trump directed his agencies to take the first steps toward reversing some of Obama's most significant climate actions, including regulations on coal miners, oil and gas drillers, and thousands of power plants.

Trump and his appointees have made no secret of their disdain for Obama’s attempts to rally the world on climate change, an issue the president has labeled a Chinese-inspired “hoax” that's wiped out American jobs. White House budget director Mick Mulvaney dismissed climate programs last month as “a waste of your money,” telling reporters that “we’re not spending money on that anymore.”

Mulvaney was defending Trump’s proposal for a 31 percent budget cut for the Environmental Protection Agency, whose carbon regulations on the power, auto, coal, oil and gas industries had provided the heart of Obama’s climate policies.

Among other steps to erase Obama's climate legacy, Trump has ordered the EPA to begin unwinding Obama’s 2015 regulations on greenhouse gases from power plants, moved toward easing the agency’s vehicle fuel-efficiency requirements and signed off on Congress’ repeal of stream-pollution restrictions that had threatened to hinder some coal mining activity. He is also due to take steps this week toward opening up vast new offshore regions for oil and gas production — a sharp break from the limits Obama imposed late in his second term.

More quietly, the administration has postponed Energy Department efficiency standards for commercial and consumer appliances such as freezers and boilers, withheld grants for research into next-generation energy technologies, and ordered the government to revise a metric called the “social cost of carbon” that seeks to factor the impacts of climate change into regulatory actions. Administration lawyers have also persuaded appellate judges to postpone rulings on several Obama-era rules facing industry challenges, giving Trump’s agencies more time to pull them back for reworking.

Rhodium's analysis of the effect of Trump’s executive order comes with plenty of caveats: It assumes that cities and states will fail to fill the gap in federal policy, and that a climate advocate will not take over the White House in 2020. It also does not allow for faster-than-expected advances in renewable energy technologies — notably battery storage — that could accelerate the shift to wind and solar power.

But Rhodium also doesn't include other measures that Trump could take, such as reneging on a 2016 treaty to limit the production of potent greenhouse gases known as hydrofluorocarbons. That agreement by itself could forestall 0.5 degrees Celsius in global warming during this century, according to U.N. estimates. The Paris agreement is meant to prevent the rise in average global temperatures from exceeding 2 degrees Celsius above pre-industrial levels.

Rhodium’s partners include Trevor Houser, who was a top outside adviser to the Clinton campaign on energy issues.

Environmental Protection Agency Administrator Scott Pruitt, left, shakes hands with coal miners during a visit to Consol Pennsylvania Coal Company's Harvey Mine in Sycamore, Pa. | AP Photo

Climate researchers say the world is so close to a tipping point that any backsliding would be dangerous.

For example, carbon dioxide levels in the Earth’s atmosphere have been hovering above 405 parts per million since November, the highest on record, according to the National Oceanic and Atmospheric Administration — significantly higher than the 350-parts-per-million level that some leading climate researchers say the world needs to move back to. The estimated change in emissions allowed by Trump's executive order would add 2 parts per million in the next 20 years, according to a rough estimate by Pieter Tans, chief of the Carbon Cycle Greenhouse Gases Group at the NOAA Earth Science Research Laboratory.

Put another way, those extra emissions alone would move the world 4 percent closer to 450 parts per million — the point at which the world still has a better-than-50-percent chance of stabilizing global temperatures, according to the Organization for Economic Cooperation and Development. Failing to stabilize temperatures would could mean intensifying extreme weather events at "unprecedented levels," the OECD says. It could also move the world to a point where temperature and emissions feedback loops make changes in the world's climate change irreversible.

"Thus far, we human beings have mostly controlled climate change through emissions of greenhouse gases," Tans said in an email. "Continuing on this path will likely lead to uncontrolled and potentially very large emissions of [carbon dioxide] and [methane] from the melting of permafrost in the Arctic, to name one plausible feedback effect."

Still, some advocates for deep cuts in carbon emissions, such as Mann, hold out hope that Obama's policies will prove difficult to uproot. They’re counting on the courts and resistant federal staffers to stall Trump's plans.

“Bureaucracy can be both a good and bad thing, depending on the circumstances," Mann said in an email. “In this case, I think it may save us.

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"Were Democrats to win back one or both houses of Congress in the mid-terms less than two years away, I think that much of the damage could almost certainly be mitigated," he added.

Skeptics of Obama’s policies argue that the U.S. would absorb most of the pain of the Paris agreement while countries such as China and India — the world’s biggest and fourth-biggest carbon polluters, respectively — would get off easy. Both countries are expected to produce more carbon dioxide in 2030 than they did in 2015.

"The Obama administration made really ambitious commitments in Paris with no clear way to get there under current regulations," said Robert Dillon, an energy expert with the American Council for Capital Formation, who contends that Trump's decision to ease off on Obama’s carbon rules puts the U.S. on a level playing field.

“Any time you have a concern where you're tying one hand behind your back to compete in the global market, there are legitimate concerns about how the country remains competitive and improves the standard of living for American families," he added.

Meanwhile, Trump’s rollback puts pressure on other countries to decide how to respond. The U.S. already butted heads with other G-7 nations this month when Energy Secretary Rick Perry's insistence that the Paris agreement should not be mentioned scuttled a joint communique.

Some foreign leaders are choosing to be optimistic, for now.

"I don't see the world backing off," Swedish Deputy Prime Minister Isabella Lövin told reporters last week in Washington. Instead she expressed concern about the next stage of the Paris agreement, which calls for nations to further cut their greenhouse gases.

"We are concerned that some might point to the U.S. and say, 'We don't have to raise ambitions now if the U.S. is not going to take part of this,'" she said. "And the U.S., of course, has a great responsibility for the historic emissions. That makes it a really bad chase to the bottom."