(CNN) Editor's Note: A version of this story first published in September 2019. The story has been updated with additional administration actions.

An impeachment trial looms and a major Middle East crisis is unfolding with Iran.

Still, the Trump administration has remained steadfast in pursuit of one of its signature policy goals: the gutting of environmental regulations, which include those aimed at curbing climate change.

From changes in early January to curb key parts of a landmark environmental protection law to relaxing restrictions on power plant emissions, Trump has attempted to remove many of the guardrails installed by the Obama and previous administrations that can limit the scope of global warming.

The world is already feeling the dangerous impacts of climate change, and has been for some time.

A massive cloud of smoke rises from wildfires burning in East Gippsland, Victoria, Australia.

Earth just endured its second hottest year on record. The typically frozen Arctic is melting at an alarming rate. And Australia is battling hellish wildfires, made even worse by global warming.

For years now, the world's top climate scientists have warned that waiting any longer to drastically cut global emissions of planet-warming gases risks exposing millions more to the worst consequences of the climate crisis -- more frequent droughts, wildfires and even food shortages.

"He is locking in permanent, irreversible damage to our environment through his irresponsible environmental policies, including his efforts to block progress on climate change," said Dr. Michael E. Mann, distinguished professor of atmospheric science at Penn State University and the director of the Penn State Earth System Science Center, said of Trump policies. "Once we go beyond key tipping points -- the melting of the major ice sheets -- there is no going back."

Here's a look at some of the most consequential climate policy rollbacks:

Overhauling a landmark law requiring environmental assessments

On January 9, the Trump administration announced plans to rewrite decades-old regulations in order to make it easier to build major infrastructure projects without considering the potential impacts to greenhouse gas emissions or of climate change, including sea level rise.

The changes announced to how the 50-year-old National Environmental Policy Act is enforced would apply to projects like pipelines, highways and mines, which had been required to undergo in-depth environmental impact assessments.

Miles of pipe for the proposed Keystone XL pipeline sit in a lot in October 2014.

According to The New York Times, Interior Secretary David Bernhardt called the changes the administration's most impactful deregulatory move yet.

The proposed changes have outraged many environmental groups, and are all but guaranteed to face legal challenges.

Weakening fuel economy standards

In 2018, the Times reported that the Trump administration was seeking to relax fuel efficiency and auto emissions benchmarks, a shift that would stamp out one of former President Barack Obama's signature climate initiatives.

If the proposed change goes into effect, it could have profound consequences for the planet: Transportation emits more greenhouse gases than any other sector of the US economy, according to the Environmental Protection Agency.

But California and several other states have sued to block the change, and there are signs that even some automakers are not on board with Trump's rollbacks.

Last year, Trump also announced he was revoking California's authority to set its own vehicle emissions standards, a move that the state's attorney general has vowed to challenge in court.

Replacing the Clean Power Plan

In a boost to electrical utilities and the struggling coal industry, Trump's move to replace Obama's Clean Power Plan could have serious consequences for the health of humans and the planet.

The Clean Power Plan placed flexible limits on carbon dioxide emissions from power plants and, according to analysis by Obama's EPA, would have reduced CO2 emissions from power generators by 32% compared with 2005 levels by 2030.

A coal plant near Baltimore spews emissions.

Trump's replacement for the Clean Power Plan is called the Affordable Clean Energy rule and allows states to set their own emissions standards for coal-fueled power plants. Last year, EPA Administrator Andrew Wheeler touted the plan, saying it gives power companies "the regulatory certainty they need to continue to reduce emissions and provide affordable and reliable energy for all Americans."

But the new rule could cost American lives. By EPA's own analysis, Trump's rule could result in 1,400 more premature deaths by 2030 than under the Clean Power Plan. Many states and cities are also suing to block the new regulations from going into effect.

Opening public lands and waters offshore to oil and gas drilling

Many scientists warn that keeping fossil fuels in the ground is critical to tackling the climate crisis. But the Trump administration has moved the US in the opposite direction, opening vast stretches of land and water offshore to oil and gas drilling.

In 2017, the administration shrank two of Utah's national monuments -- Grand-Staircase Escalante National Monument and Bear's Ears -- by 51% and 85%, respectively. The moves took land areas spanning twice the size of Rhode Island out of protected status and were part of the largest reduction of public lands in US history, according to a study published in the journal Science. The changes open the areas removed from the national monuments to oil and gas development, but both decisions face challenges in court.

The vast wilderness of the Arctic National Wildlife Reserve is seen from a plane.

The administration has also pushed to open Alaska's Arctic National Wildlife Refuge to oil and gas exploration, as well as waters offshore along the East and Pacific coasts, and the Arctic.

"The pipeline projects potentially lock in long-term extraction of natural gas and petroleum, and therefore have a very long legacy that will extend beyond the next administration," Mann said.

Pulling out of the Paris climate agreement

Trump's move to begin formally pulling the US out of the landmark Paris climate accord, which was agreed to by nearly all of the world's countries, was a major blow to the global response to the climate crisis.

The decision sent a message to the rest of the world that the US -- which can't officially leave the agreement until the day after this year's presidential election -- would not be leading the global fight against climate change. And studies have shown the decision has had global implications: A report last year found that Trump's decision has made it easier for other countries to renege on their climate commitments.

Loosening restrictions on methane emissions

Last year, Trump's EPA announced that it would no longer require oil and gas companies to install monitors that detect methane leaks from new wells, tanks and pipelines.

A fracking rig near Waynesburg, Pa. is shown in 2012.

At a time when the US has become the world's biggest natural gas and oil producer, the move is significant because of the potency of methane's heat-trapping capabilities. Though the gas doesn't last in the atmosphere as long as CO2, 1 ton of methane has 84 to 87 times more global warming potential than the same amount of CO2 over a 20-year period.

Delaying ratification of a treaty on hydrofluorocarbons

Another key global agreement to limit planet-warming gases went into effect last year, but Trump has yet to send it to the Senate to ratify it.

The treaty is called the Kigali Amendment, and it deals with a little-known but highly potent class of greenhouse gases called hydrofluorocarbons (HFCs), which are used in refrigerators and air conditioners. The gases are sometimes called "super greenhouse gases" because of their capacity to trap huge amounts of heat in the atmosphere; they have more than 1,000 times greater warming potential than carbon dioxide.

The climate change solutions organization Project Drawdown has found that phasing out these chemicals would be the most impactful solution to stop global warming -- more than eating less meat, driving electric cars or switching to renewable energy.