The Trump administration is expected to propose rolling back the Clean Power Plan today, a major step back from policies put in place by the Obama administration to combat climate change.
So what could that mean for the environment?
The biggest criticism of undoing the plan is that continuing emissions at current levels would not slow down rising global temperatures, which could lead to further consequences that hurt the environment and public health.
The goal of the Clean Power Plan was to reduce 2005-level carbon dioxide emissions by 32 percent by 2030. States would be required to submit plans on how they would reduce emissions through options like adding new technology to power plants or switching to energy sources like wind or solar.
In 2015, carbon dioxide emissions from energy were 12 percent lower than levels in 2005, according to the U.S. Energy Information Administration.
President Barack Obama said the additional reductions would be "like cutting every ounce of emission due to electricity from 108 million American homes. Or it's the equivalent of taking 166 million cars off the road," in his speech announcing the plan in 2015.
The Obama administration said the regulations would decrease pollutants that cause soot and smog, which would lead to fewer asthma attacks in children and fewer premature deaths, according to a White House fact sheet.
The Clean Power Plan hasn't gone into effect yet, so there is no data to show if it had an impact on emissions.
Carbon dioxide and other gases stick around in the atmosphere after they are released from burning fossil fuels. Those gases trap heat, which in turn makes temperatures around the world go up, a phenomenon called the "greenhouse effect."
In the Paris Climate Agreement, 196 parties, including the U.S. at the time, agreed to work together to keep temperatures from rising more than 2 degrees.
The half degree difference between a 1.5- and a 2-degree temperature increase is when most scientists agree we would start to see serious consequences, like rising sea levels that threaten coastal cities, longer heat waves and the death of tropical coral reefs, according to research from the European Geosciences Union.
President Trump criticized that difference as "tiny" when he announced that the U.S. would leave the Paris Climate Agreement.
More than half of Americans also believe changes in the climate as responsible for the severity of recent hurricanes, according to an ABC News/Washington Post poll conducted in mid-September. Research published in the Proceedings of the National Academy of Sciences earlier this year found that warmer temperatures and sea level rise have made severe weather events more serious, but it's difficult to show that that is the only factor.
It's unlikely that the country will see any immediate effects from rolling back the Clean Power Plan. The rule withdrawing it will be posted for a public comment period on Tuesday and the EPA could look at further feedback for any replacement. There will also likely be legal challenges from environmental groups seeking to save the rule.
Many state and local officials have also said that they will work to reduce emissions even if the Trump administration cancels national climate policies. Mayors of at least 381 cities have pledged they would stick to the goals of the Paris Agreement after Trump announced the U.S. would withdraw, as have the governors from at least 10 states, as well as CEOs from major companies.