(CNN) In almost every corner of his administration, President Donald Trump has veered sharply from the policies of his predecessor -- and even past Republicans.

But his rollback of regulations designed to limit global warming is one of the clearest ways he has worked to erase a cornerstone of President Barack Obama's legacy.

From promising to leave the landmark Paris climate accord to relaxing restrictions on power plant emissions , Trump has attempted to remove many of the guardrails installed by the Obama administration to limit the emissions of greenhouse gases.

Last fall, the world's top climate scientists warned that we have barely more than a decade to drastically cut global carbon emissions , to avoid facing the worst consequences of the climate crisis -- droughts, wildfires and food shortages impacting hundreds of millions of people.

Regardless of what happens in the 2020 presidential election, critics say Trump has already cemented an environmental legacy that will be felt by generations to come.

"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. "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 Trump's most consequential climate policy rollbacks:

Weakening fuel economy standards

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

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 (CPP) could have serious consequences for the health of humans and the planet.

The CPP 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 percent compared to 2005 levels by 2030.

A coal plant near Baltimore spews emissions.

Trump's replacement for the CPP is called the Affordable Clean Energy rule and allows states to set their own emissions standards for coal-fueled power plants. Earlier this 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 CPP. 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 Ears -- by 51% and 85% respectively. The moves took land areas spanning twice the size of Rhode Island out of protected status and was 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 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

The decision sent a message to the rest of the world that the US -- which can legally leave the agreement as early as 2020 -- 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

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

Delaying ratification of a treaty on hydrofluorocarbons

Another key global agreement to limit planet-warming gases went into effect earlier this 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