Oil pumps and natural gas burn off in Watford City, N.D. (AP Photo/Charles Rex Arbogast, File)

Across the globe, climate change activists are watching closely whether a Donald Trump administration would halt recent progress toward slowing the warming of the planet. The main focus thus far has been on the prospect that Trump would withdraw from the international Paris climate agreement and hobble the domestic Clean Power Plan.

Yet Trump is also expected to seek to reverse or undermine another set of Obama policies meant to curb climate change that focus not on carbon dioxide, the most notorious greenhouse gas, but rather methane — the second most important one. It’s the main component of natural gas, and actually causes a much larger amount of global warming than carbon dioxide does, at least over short time periods, although it does not last nearly as long in the atmosphere.

One key concern has been that considerable volumes of methane have been leaking into the atmosphere from oil and gas operations, which have seen a boom in the United States in recent years. Precisely how much methane is being released, and why, remains controversial. But this has triggered a contentious move towards regulation that Trump could now try to reverse.

“Methane is a top priority and we’ll be pursuing that aggressively,” said Jack Gerard, the president of the American Petroleum Institute, on a conference call with reporters Thursday. Gerard said recent Obama administration methane regulations have added “unnecessary cost and confusion and it seems to demonstrate no benefit for all the associated cost,” arguing the rules often overlap with regulations that states already have in place.

The Environmental Protection Agency recently revised upwards its estimates of methane emissions coming from the oil and gas industry, rendering it the largest source of U.S. methane emissions (other sources include wetlands, landfills, and most importantly, ruminant animals like cattle). However, the American Petroleum Institute has contested that revision.

More generally, it must be acknowledged that our understanding of the sources of methane in the atmosphere is less advanced than is our understanding of the sources of carbon dioxide. This is an area where there remains much science to be done in order to figure out more precisely what is happening. For instance, one recent study suggested the recent growth of atmospheric methane levels is attributable not to the oil and gas sector, but rather, might be due to global agriculture.

But in the meantime, the Obama administration has launched a multi-pronged regulatory approach that has garnered considerable industry ire.

Last year, Obama pledged to reduce U.S. oil and gas methane emissions by 40 to 45 percent below their 2012 levels by the year 2025, a move that would rely on a number of distinct policies. First, the EPA under Obama enacted new regulations earlier this year aimed at leaks from new and modified oil and gas equipment, a set of rules the agency says will avoid the emission of “510,000 short tons of methane in 2025, the equivalent of reducing 11 million metric tons of carbon dioxide.”

But that’s just the beginning: The agency is next planning to target existing rigs and wells, and has already sent out a request to the industry for information to guide regulation. However, the EPA isn’t expected to finish that work before leaving office.

Meanwhile, the Interior Department’s Bureau of Land Management has also been proceeding on regulations to require methane emissions if companies want to drill on U.S. public lands. That regulation, it estimates, would prevent another 164,000 to 169,000 tons of emissions of methane annually. Converting that to carbon dioxide, the agency says would be the equivalent of 4.1 to 4.2 million metric tons.

It would appear that Trump would want to reverse as much of this as he can. Trump energy adviser Kevin Cramer, a U.S. representative from North Dakota, the center of the domestic oil and gas boom, recently told the trade service Platts that the oil and gas industry is feeling “tremendous renewed optimism, I can tell you that. The commitment to rolling back regulations and returning more oversight back to states, things like the fracking rule, methane emissions rules, for example. There’s just a renewed optimism that [US producers] are going to be unshackled from over-regulation.”

statement on energy policy put up on the Trump transition website does not explicitly mention the issue of methane regulations, but says that “We will lift the restrictions on American energy, and allow this wealth to pour into our communities. It’s all upside: more jobs, more revenues, more wealth, higher wages, and lower energy prices.”

This language is almost exactly the same as what Trump said in September when speaking in Pittsburgh at a shale industry conference in Pittsburgh. “If you ask yourself what he’s talking about, what are the restrictions, the methane rules are the highest cost factor of rules that were under consideration for shale oil and gas development,” said Scott Segal,  a partner at Bracewell LLP who works on energy regulatory issues.

But what could Trump actually achieve? It turns out that each of the Obama policies in question need to be treated rather distinctly.

First, the current EPA rules, which only apply to new and modified oil and gas equipment, are already final, said Mark Brownstein, vice president of climate and energy at the Environmental Defense Fund.

“It would be no easy thing for the incoming administration to revisit the new source rule, as it is now an adopted regulation,” he said. “So it would require rule-making, and the same standards of administrative procedure that led to the adoption of the rule would apply to any effort to modify it our repeal it. In other words, you can’t simply propose changes in an arbitrary and capricious way.” So this regulation might be the hardest to reverse.

The Interior Department regulation covering public lands, however, is only proposed, not finalized. It could come out soon, before the change of administrations.

That itself would be contentious: Segal suggests that from the Trump administration’s perspective it would be desirable to have a hold or moratorium on new regulations at the close of the Obama years. “It’s not unusual for there to be a moratorium on major rules, and Democratic and Republican administrations have done that,” he said. “I would go so far as to say that it’s standard operating procedure to freeze major rules.”

So it remains to be seen whether this rule is finalized before the end of the Obama administration — and if so, what kind of fight that triggers.

Finally, Brownstein says, in order to get to the Obama goal of reducing all oil and gas methane emissions by 45 percent, there would have to be an additional regulation on existing oil and gas sources of methane, which the agency is contemplating, but no one expects to be finalized under Obama.

As far as these last and most sweeping regulations go, “I won’t sit here and pretend that that task has gotten easier in the last 48 hours,” Brownstein said. But he added, “I think we can make a pretty good case that there’s a lot of benefit to U.S. energy economy from moving forward with this.”

This regulation is, potentially, the big one – and it’s the least likely to happen now. “A rule that addressed all well pad and infrastructure would be much more important than rules focusing just on federal lands and new well pad construction. That’s an enormous contrast,” said Rob Jackson, a researcher at Stanford University who studies emissions from the natural gas sector.

Thus, it does seem clear that the Trump administration can significantly curtail at least some of Obama’s existing or intended methane regulations. The question then becomes what would happen by doing so — environmentalists clearly think more of the gas would pour forth, but industry counters that there is a strong built-in incentive to capture methane (it is, after all, valuable fuel). This has been their argument against the regulations all along — they aren’t needed.

Still, Obama’s 45 percent reduction target for methane emissions by 2025 now appears unlikely to happen, says Stanford’s Jackson — who noted that if all countries were to adopt a goal so ambitious it would reduce 10 percent of global methane from human activities.

“I’m convinced that we’ll continue to see improvements based on the economics, and on companies’ desire to improve things,” said Jackson. “I’m skeptical that we’ll see anything nearly that ambitious though.”