The move to rescind environmental rules governing emissions of methane, a powerful greenhouse gas, brings to 84 the total number of environmental rules that the Trump administration has worked to repeal. Officials at the White House, the Environmental Protection Agency and other agencies have called the regulations burdensome to the fossil fuel industry and other businesses.

Half of those environmental rollback attempts, like the new methane reversal, will undercut efforts by previous administrations to reduce emissions and fight climate change. Many of these efforts have been challenged in the courts; whether the administration will succeed in achieving all of its goals is far from certain. Here are some of the most significant climate-related reversals:

Leaving the Paris climate agreement

One critical effort by the Trump administration was its announcement in 2017 that it would withdraw the United States from the Paris climate agreement. The process of withdrawing cannot be completed until 2020, but the move sent a strong signal to the world that Mr. Trump, who has scoffed at climate science, would be taking action at many levels of government to reverse climate policies created during the Obama administration.

Weakening methane regulation

Thursday’s decision to remove restrictions on methane leaks from oil and gas wells is only one administration effort on behalf of fossil fuel producers. Burning natural gas produces half of the carbon dioxide that burning coal does, but methane, the chief component of natural gas, has a powerful effect on climate change. Though it does not persist in the atmosphere as long as carbon dioxide does, it has 80 times the heat-trapping power of carbon dioxide during 20 years in the atmosphere. The Obama administration had passed many rules to reduce methane leaks. An early effort by the E.P.A. under the former administrator Scott Pruitt to reverse Obama-era rules on leaks from new oil and gas wells was declared illegal by the courts in 2017.

Freezing fuel efficiency standards

Transportation is the United States’ biggest source of greenhouse gas emissions, and fuel efficiency standards were a signature Obama administration proposal for reducing those emissions, as well as other air pollution created by vehicles. Earlier this month, the Trump administration proposed freezing antipollution and fuel-efficiency standards for cars. The proposal puts the administration on a collision course with California, which sets its own stringent tailpipe standards — and even with automakers, who wish to avoid the complexity of dealing with two car markets with different emissions standards.