(CNN) It has been a noteworthy year for US environmental policy.

A number of Obama-era rules and regulations governing the US approach to climate change and its natural resources have been the target of President Donald Trump's deregulatory fervor. The Environmental Protection Agency, reportedly plagued by internal drama, saw a steady overhaul of its credo. Trump announced plans to withdraw from the US commitment to the Paris climate agreement.

Here is a look back at some of the most notable changes from 2017.

Pulling out of the Paris climate agreement

By the end of 2017, the United States stood alone on the landmark Paris climate pact. As of November, it was the only nation in the world not committed to the deal.

Trump announced his intention to abandon the accord in June, a process that will be complete in 2020.

"We're getting out," he said. "And we will start to renegotiate and we'll see if there's a better deal. If we can, great. If we can't, that's fine."

The deal, which was agreed on by nearly 200 countries in 2015, is dedicated to lowering emissions and strengthening countries' abilities to deal with the effects of climate change. The United States is second only to China in terms of carbon dioxide emissions.

The accord was a keystone of former President Barack Obama's legacy. He slammed Trump's decision to withdraw from it, saying in a statement that the agreement was intended to "protect the world we leave to our children."

A chorus of world leaders expressed their disdain at Trump's move, and mayors and governors throughout the US vowed to carry on the commitments of the climate accord in their own jurisdictions.

Changes at the EPA

The Environmental Protection Agency underwent a radical transformation this year.

Administrator Scott Pruitt , who sued the agency many times as Oklahoma's attorney general, has steered it toward deregulation efforts and has taken significantly more meetings with fossil-fuel industry leaders than with environmental groups.

Pruitt has also shied away from robust action on climate change. He has acknowledged that climate change is occurring but has questioned the extent to which it is caused by human activities and the authority of his agency to regulate it.

The phrase "climate change" did not appear in the agency's draft four-year strategic plan. It instead prioritizes a focus on the "core mission" of clean air, land and water; a "rebalance" of the federal role in environmental regulation, shifting more of the responsibility to states; and enforcement of laws "as Congress intended."

Trump has proposed a 30% budget cut for the agency, including major reductions to its enforcement work and staffing, as well as the elimination of some programs. CNN obtained an internal report in April outlining a plan to reduce the EPA workforce through buyouts and early retirement. The New York Times reported that hundreds of employees left the agency this year.

Rolling back the Clean Power Plan

In October , Pruitt announced plans to repeal the Clean Power Plan. The Obama-era rule requires states to meet specific carbon emission reduction standards based on their individual energy consumption. It includes an incentive program for states to get a head start on meeting standards for renewable energy and low-income energy efficiency.

Pruitt argued against the legality of the original rule, saying it exceeded the agency's authority.

"We are committed to righting the wrongs of the Obama administration by cleaning the regulatory slate. Any replacement rule will be done carefully, properly, and with humility, by listening to all those affected," Pruitt said in a statement. No replacement was announced at the time.

Environmental groups and the former EPA administrator blasted the proposed repeal.

"A proposal to repeal the Clean Power Plan without any time line or even a commitment to propose a rule to reduce carbon pollution, isn't a step forward, it's a wholesale retreat from EPA's legal, scientific and moral obligation to address the threats of climate change," former Administrator Gina McCarthy said in a statement.

Scaling back national monuments

In early December, Trump signed two presidential proclamations to shrink the Bears Ears and Grand Staircase-Escalante national monuments.

The proclamations split the two monuments into several smaller sections. Bears Ears, designated by Obama in 2016, will be shrunk from 1.35 million acres to 228,337, according to a spokesperson for Interior, and split into two separate monument sections. Grand Staircase-Escalante, designated by President Bill Clinton, will be split into three sections and shrunk from 1.9 million acres to about 1 million.

Shrinking the monuments opens the land up for oil and natural gas extraction. Trump said his decision was made to "reverse federal overreach and restore the rights of this land to your citizens."

A group of Native American tribes, conservation groups and others have filed suits against the Trump administration over the proclamations.

Big wins for oil

The oil industry saw a number of big victories in the first year of the Trump administration.

In March, the administration approved a permit to construct the controversial Keystone XL pipeline , which had been blocked by Obama. The proposed pipeline would run from Hardisty, Alberta, southeast to Steele City, Nebraska, and would connect with other pipelines in the system.

Environmentalists opposed the construction of the pipeline due its reliance on Canadian oil sands, which release more greenhouse gases than standard oil extraction. They are also concerned because the proposed route would cut across the Ogallala Aquifer, one of the world's largest underground deposits of fresh water, meaning potential contamination if there were a leak. Native American groups argued that the pipeline would run across sovereign, sacred lands.