Whether the U.S. meets its emissions-reduction commitments under the Paris climate accord is pivotal to the success of the global agreement, but the Trump administration's policies have all but ensured the U.S. will fall far short. One recent analysis says the country will miss its target by more than 1 billion metric tons.

Under President Barack Obama, the United States pledged to reduce greenhouse gas emissions 26-28 percent from 2005 levels by 2025. That means emissions must be cut about 1.7 billion metric tons, according to figures from the Environmental Protection Agency's latest greenhouse gas inventory. The nation is a third of the way to that target, but the rest was to be achieved via an array of regulations, especially the Clean Power Plan, that are now targeted for elimination by President Donald Trump. Not only was the goal dependent on those rules, it would have also required even more rigorous policies from Obama's successor because reductions from those rules would not have been enough, numerous studies have found.

David Bookbinder, a longtime environmental lawyer and a fellow at the libertarian think tank the Niskanen Center, released a new analysis that puts the shortfall at 1 billion metric tons if Trump succeeds in undoing most of the Obama-era climate rules. Meaning, emissions from the world's second-largest carbon polluter would be virtually unchanged from today. That would jeopardize any chance the world has to set a course of deep and rapid decarbonization over the next critical few years.

"There were people at the [EPA] hard at work on 2.0 [of climate policy], and they were going to ratchet it up, and it was going to be justified by Paris. It all would have worked, except for that whole election thing," Bookbinder said. "Now, it's all over...We're at square zero."

InsideClimate News compiled a chart showing exactly how far the United States still has to go to meet its Paris pledge. We discovered that the U.S. has already achieved an emissions reduction of 572 million metric tons, a third of the Paris target. That was largely the result of coal being driven out of the market under competitive pressure from natural gas and renewables, greater efficiency throughout the economy and a broad range of regulations. Most of the remaining two-thirds counted on the Clean Power Plan and other Obama-era rules. Even if those were implemented, the chart shows, the U.S would still fall 17 percent short of meeting its Paris pledge.

(This analysis is based on estimates by the scientists at the Lawrence Berkeley National Laboratory of the maximum emissions cuts achievable with each of Obama's policies. Other analyses and studies by groups including the World Resources Institute and the U.S. Chamber of Commerce have come up with different numbers. But all agreed that further policy would be needed to make the goal.)

Some important Obama climate efforts are expected to survive under Trump and state efforts also could help. California's ambitious carbon-cutting policies, for instance, would be enough to cut emissions an estimated 78 million metric tons, according to an analysis by scientists at the Berkeley Lab, which was published in Nature Climate Change. That's enough to contribute 4 percent of the emissions cuts needed to meet the Paris accord. But legal battles with both industry and the Trump administration are brewing for California, and no other single state has the market clout of the Golden State, the sixth-largest economy in the world.

(The lab's analysis is based on the state's 2015 law increasing its renewable portfolio standard to 50 percent and doubling building energy efficiency by 2030, as well as a 2016 law reducing its emissions 40 percent from 1990 levels by 2030.)

Here's a breakdown of the Obama administration policies and their likely fate under Trump:

The Clean Power Plan

The EPA regulation to dramatically cut carbon emissions from power plants, finalized in 2015, is the single most important U.S. initiative. The Berkeley Lab researchers estimated it could reduce carbon emissions by as much as 267 million metric tons, contributing as much as 15 percent of the emissions cuts needed to achieve the nation's Paris pledge. An executive order is expected any day declaring the administration's intention to repeal the rule. Repeal, however, requires another rulemaking procedure to undo it, with public notice and comment. The EPA will have to justify it, and the agency inevitably will be challenged in court by environmental groups and others, in a process that could take years.

A federal appeals court, however, is also weighing a legal challenge to the CPP, which was stayed by the Supreme Court. That ruling, awaited for weeks, could make Trump's job in eliminating the rule easier or harder.

Air conditioning and refrigeration (HFCs)

When 170 nations agreed last October in Kigali, Rwanda, to curb emissions of the refrigeration gases called HFCs, then-secretary of state John Kerry called it the "single most important step that we could take at this moment to limit the warming of our planet." The Berkeley Lab said that the Kigali amendment to the Montreal Protocol, along with the so-called Significant New Alternatives Program rules finalized in 2015, are second only to the Clean Power Plan in potential for cutting U.S. greenhouse gas emissions.

Many analysts believe that the Trump administration will keep the HFC rules in place and that if the Kigali amendment is sent to the Senate it will be ratified. That's because two U.S chemical companies that make alternatives, the DuPont spinoff Chemours and Honeywell International, support the HFC phase out.

Methane regulations

The Obama administration had set a high goal of a 40 to 45 percent reduction of methane from 2012 levels in the oil and gas industry. Because methane, the main component of natural gas, is at least 25 times more potent than carbon dioxide as a heat-trapping gas, small steps to cut emissions can have a big impact. And no advanced technologies are needed to plug methane leaks from oil and gas processing equipment and distribution pipes. But the industry has fiercely opposed federal regulations, saying its voluntary steps to capture methane are sufficient.

Under Obama, the EPA only finalized one initiative—standards for new oil and gas facilities—and the much more ambitious task of addressing methane leaks at 700,000 existing U.S. oil and gas facilities was stopped in its tracks by new EPA chief Scott Pruitt. He ended the industry information collection effort needed to lay the groundwork for the rulemaking.

Fuel economy standards

President Trump traveled to Detroit last week to announce a rollback of strict U.S. fuel economy standards for cars and trucks that were put in place by the Obama administration. It was a striking turnaround from eight years earlier, when the carmakers—then desperate for a government bailout—agreed to increase the efficiency of their fleet.

Under the rules finalized in 2012, the first change in fuel economy standards in 25 years, automakers were to double vehicle fleet mileage to 54.5 miles per gallon by 2025, a move that the EPA expected would cut more than 6,000 million metric tons of greenhouse gases—more than one year's worth of total U.S. carbon emissions—over the lifetime of the vehicles sold from model years 2011 to 2025. The Obama administration had estimated that the fuel economy standards would account for 140 million metric tons of emissions cuts by 2025, which adds up to 8 percent of the cuts needed to meet the Paris pledge. (The Berkeley Lab and our chart did not estimate how much carbon the standards would save; its model assumed that the regulations were firmly in place and now part of "business-as-usual" scenarios.)

Trump's intentions for the first-ever efficiency standards for heavy trucks finalized last August, are still unknown. The Berkeley Lab estimated that could save as much as 48 million metric tons of emissions by 2025, or 3 percent of the savings needed for the Paris pledge.

Building and appliance standards

Obama's Energy Department finalized more standards for energy efficient appliances and products than in any past administration, according to at least one analysis. The Berkeley Lab found they could save as much as 114 million metric tons of emissions, or 7 percent of the cuts needed for Paris. Four of those standards were swept up in the regulatory freeze put into place on Trump's first day in office, and his budget blueprint included his proposal to kill Energy Star, a popular voluntary labeling program that helps consumers pick appliances that use less electricity.

Clarification: This story was updated to clarify the California policies included in this analyis, as well as the reasons for not including the carbon savings from the 2012 fuel economy standards.