Before Donald Trump had even unpacked at the White House, his administration was making it clear he intended to follow through on campaign pledges to unravel climate regulations (see “President Trump Takes Immediate Aim at Obama’s Climate Action Plan”).

On Inauguration Day, the URL to the White House climate page went dead as a new page declaring "An American First Energy Policy Plan" appeared. It promised to boost domestic energy exploration and production, and cut climate-related and environmental rules.

In the nearly one year since, President Trump and his cabinet appointees have worked diligently to fulfill that vow, stunting burgeoning efforts to cut the greenhouse-gas emissions fueling global warming.

In a long list of energy policies, actions, and leaked intentions, some of which may or may not come to pass, it’s difficult to predict what will ultimately have the biggest impact. But here’s our best effort to identify the five things that could most significantly undercut efforts to reduce the risks of climate change, and undermine the nation’s leadership on some of the defining technologies of the century ahead.

Forsaking global leadership

On June 1, Trump announced plans to withdraw from the Paris climate accords, a landmark global agreement to strive to keep worldwide temperature increases below 2 ˚C this century. He also said the United States would halt billions of dollars in pledged contributions to the Green Climate Fund, an effort to help poorer nations cut greenhouse-gas emissions.

As others have pointed out, the direct impact of the announcement is mitigated by several factors. The global pact was nonbinding in the first place, and the administration was already attacking the policy levers by which President Obama hoped to achieve the reductions. In addition, the earliest the United States can officially exit the deal is one day after the next presidential election (which means the election will be, in part, a referendum on the Paris agreement itself).

But the announcement alone could encourage other nations to take their own commitments less seriously and dissuade them from adopting stricter emissions reductions goals in the years to come.

The bigger danger for the United States could be that it’s effectively ceding its leadership on climate and energy to other nations, particularly China. That may mean giving up access to global markets and relinquishing influence over issues in our national interest. In addition, it could slow U.S. advances in energy technologies such as carbon capture, advanced nuclear reactors, next-generation solar, and grid-scale energy storage, noted Jason Bordoff of Columbia University’s Center on Global Energy Policy in a commentary in Nature Energy.

Indeed, some nations have already leveraged the Trump administration’s open hostility toward science, and scientists, to lure U.S. researchers overseas. In December, French president Emmanuel Macron announced that the nation was awarding millions of dollars in grants to 13 American scientists to conduct climate research in France as part of his “Make Our Planet Great Again” initiative.

RICH | FLICKR

Propping up coal

In September, Energy Secretary Rick Perry submitted a notice of proposed rulemaking that would essentially subsidize power plants that can stockpile more than 90 days’ worth of fuel on site—which was another way of saying coal and nuclear plants.

The stated rationale was to prevent the closure of big power plants crucial to grid reliability, particularly during disasters. But that reasoning flies in the face of the Department of Energy’s own report earlier this year that concluded grid reliability is improving, even as coal plants shutter. Subsidies are also a strange prescription for an administration that has often said the government shouldn’t pick winners and losers. Meanwhile, other energy researchers have repeatedly found that a wider array of energy generation sources, balanced across a redundant network of long-range transmission lines, offers far greater reliability.

Using taxpayer funds to subsidize coal at a point when we need to cut greenhouse-gas emissions as quickly as possible isn’t just irresponsible on climate grounds. An analysis by Resources for the Future found it would prevent the retirement of around 25 gigawatts of particulate-emitting coal plants, cause 27,000 premature deaths, and cost end users $75 billion.

The Federal Energy Regulatory Commission is set to make a decision on the proposal early in 2018.

VCU CNS | Flickr

Vehicle mileage standards

As nations like China, France, and Britain take steps to outlaw combustion-engine vehicles altogether in the decades ahead, the Trump administration is trying to roll back fuel economy standards.

In the waning days of the Obama administration, the Environmental Protection Agency finalized rules requiring auto manufacturers to raise their fleet-wide average for cars and light vehicles to 54.5 miles per gallon by 2025.

But in March, the EPA reopened a review of those rules, raising the likelihood that the agency will hold the current standards in place, or at least lower the proposed targets early next year.

The change would be a huge blow to emissions goals. In 2012, the EPA estimated that enacting those new standards would cut 140 million tons of greenhouse gases in 2025, or nearly two billion tons over the preceding eight years (see “How Much Damage Could Scott Pruitt Really Do at EPA?”). Some of the damage could be offset by state mileage standards, assuming the EPA doesn’t successfully challenge the waivers that allowed them.

Scott Pruitt

Clean Power Plan

As Oklahoma’s attorney general, Scott Pruitt sued the Environmental Protection agency to block the Clean Power Plan, President Obama’s signature climate policy and one of the most important tools in meeting the nation’s commitments under the Paris climate accords.

So it came as a surprise to precisely no one when Pruitt, as Trump’s appointed head of the agency, signed an order to repeal the measure in October.

It could be one of the most consequential shifts under Trump so far, slowing the retirement of coal plants and discouraging investments in cleaner energy generation, says Robert Stavins, director of the Harvard Environmental Economics Program.

The rule, already on hold amid legal challenges, required the electricity sector to cut carbon pollution to 32 percent below 2005 levels by 2030. That could have accounted for as much as 267 million tons of greenhouse-gas reductions in 2025, around 15 percent of what could be needed to meet U.S. targets under the Paris deal, according to a 2016 study by the Lawrence Berkeley National Lab.

Some models suggest that the nation will hit the Clean Power Plan targets even without the rule as long as natural-gas prices stay low, which has been a crucial factor shuttering coal operations for years. But whether or not the rule was necessary to reach the specified emissions goals in the first place, its implementation would have raised the brighter possibility that the electricity sector would ultimately exceed those mandates.

NATIONAL RENEWABLE ENERGY LAB | FLICKR

Defunding energy research

The White House’s fiscal 2018 budget proposal slashed research funding for the Department of Energy by more than $3 billion and eliminated the Advanced Research Projects Agency-Energy, the department’s moonshot energy investment arm (see “Will ARPA-E Survive Trump’s Looming Budget Cuts?”). Congress has pushed back against the deepest cuts, but it’s clear that funding will take a hit—and the fate of ARPA-E remains up for grabs as congressional negotiations stretch on.

Despite the penetration and price gains of renewables in recent years, there are still big technological holes preventing major parts of the economy from affordably going green. Among the major missing pieces are sustainable liquid fuels, cheap baseload storage, and scalable carbon capture systems.

Slashing investments in early-stage energy research will lengthen the time it takes to achieve crucial breakthroughs—or allow researchers or companies in other nations to get there first, locking down massive markets and global influence in the process.