President Donald Trump has said he believes climate change is a hoax.
So it's no surprise that Trump's EPA administrator, Scott Pruitt, is working to roll back the Clean Power Plan— former President Barack Obama's signature pollution-curbing legislation.
Since entering the White House, Trump's administration has made efforts to revoke or reverse at least 52 Obama-era environmental polices aimed at fighting the gradual warming of the planet.
Trump has called these polices "stupid" and claimed they are unfair to the fossil fuel industry. The administration's long string of regulatory rollbacks have also been accompanied by the green-lighting of several projects that Obama had blocked because of their potential negative impacts on the climate.
Here are some of the most important changes:
What the rule did: The centerpiece of Obama's climate change policy was designed to curb pollution from coal- and gas-fired power plants. It would have required states to create comprehensive plans to reduce their emissions from energy generation, a strategy that researchers estimated would slash that type of pollution — which currently accounts for a third of all US carbon emissions— by 32% by 2030.
Current status: In March, Trump issued an executive order instructing the EPA to reassess the plan, which has yet to take effect due to legal complications. In October, the EPA said it would repeal it.
What the rule did: Required US government agencies to meet higher flood standards when designing and constructing new roads, bridges, and housing developments. Trade groups and several Republican lawmakers said the rule was too costly, but the Obama administration estimated it would have raised construction costs by 0.25% to 1.25%.
Current status: Revoked as of August.
What the rule did: Under Obama, the rule banned new coal leases on federal public land, a move the coal industry opposed. However, coal use and production has been declining for years for economic reasons — it is more expensive and less efficient in most parts of the country than natural gas and wind. Coal burning is also the largest source of carbon emissions from electricity generation in the country.
Current status: Revoked as of March.
What the rule did: Obama delayed construction of the Dakota Access Pipeline (DAPL), a 1,200-mile oil project that shuttles North Dakota oil to refining markets in Illinois. The pipeline crosses Lake Oahe, a burial site sacred to the Standing Rock Sioux and a major source of the community's drinking water.
Current status: Trump expedited the pipeline's construction in January and it started running on June 1. Later that month, a federal judge ordered another environmental review, meaning it could close at a later date.
What the rule did: Keystone XL, a $10-billion new segment of the existing Keystone Pipeline system, was designed to move more oil from the Alberta, Canada, oil sands to several areas in Canada and Texas. The pipeline allows the oil to be transported faster in wider pipes on a shortened route. Obama rejected the project in 2015, citing its contribution to climate change, but an assessment from the State Department found it would release, at most, an extra 27.4 million metric tons of carbon pollution each year — 0.4% of the country's total.
Current status: State regulators in Nebraska voted to allow Keystone XL to proceed on an alternate path through their state in November — removing the final big obstacle for the project's completion. The decision was made just weeks after the existing Keystone pipeline leaked 210,000 gallons of oil in South Dakota.
What the rule did: Using an obscure provision of a 1953 law, Obama banned offshore oil and gas drilling along wide swaths of the Arctic and the Atlantic seaboard, where several endangered species, including polar bears, live. Oil and gas industries opposed the move; environmentalists praised it.
Current status: In April, Trump signed an executive order that he said would reverse the ban. The final version of the Republican tax reform bill will likely include a provision allowing drilling in the Arctic National Wildlife Refuge.
What the rule did: Economists have struggled for years to measure the cost of carbon pollution. That's where a concept called the social cost of carbon (SCC) comes in. The figure attempts to quantify the effects of CO2 emissions by estimating changes in future agricultural productivity, human health, property damage from floods and storms, and changes in energy costs. Under Obama, the SCC was pegged at about $42-$45 per ton by 2020, and the number was used to inform a variety of regulations like fuel-efficiency standards.
Current status: In February, Trump directed agencies to stop using the metric to guide regulations. Members of the Trump administration have said the figures the Obama administration used were too high, though a recent study reassessed how the figure calculated agricultural impacts and found it may have been far too low. The current EPA's proposed repeal of the Clean Power Plan suggests the number will be reduced to between $1 and $6 per ton.
What the rule did: Required oil and gas producers to report their emissions of methane, a potent greenhouse gas that gets released during the fossil fuel extraction process. Although methane accounts for just 9% of overall greenhouse gas emissions and doesn't stay in the atmosphere as long as carbon dioxide, it traps 30 times more heat per ton than CO2 does.
Current status: Cancelled as of March.
What the rule did: Raised the fuel efficiency standards for cars and trucks by requiring them to get an average of 54.5 miles per gallon by 2025 — up from 27.9 mph in 2011. The Obama administration said the measure would have halved greenhouse gas emissions by 2025. Automakers said the measure was too costly; environmentalists said it wasn't strong enough.
Current status: The Trump administration has reopened a review of the standards for cars produced between 2021 and 2025. The EPA announced in August that the agency is considering rewriting the standards to be more relaxed.
What the rule does: The global accord requires all countries who signed it to come up with plans to stop the planet from warming by more than 2 degrees Celsius above preindustrial levels. Scientists have set that key threshold as a point after which it would be very difficult to prevent extreme heat waves and storms. With Obama's 2015 signature, the US set a goal to reduce greenhouse gas emissions by 27% by 2025 relative to 2005.
Current status: Trump formally announced his intent to withdraw the US from the Paris Agreement in June, but according to the agreement's rules, the earliest the US could officially exit is November 4, 2020 — the day after the next presidential election. If the US does go through with the withdrawal, it would be the only country in the world not signed on.
Announced plans to dramatically reduce the size of Bears Ears and Grand Staircase National Monuments
What the rule does: Obama used the Antiquities Act— which allows presidents to preserve "objects of historic or scientific interest" as national monuments — to protect roughly 4 million acres of land and several million square miles of ocean.
Current status: In December, Trump announced that Bears Ears will be reduced by 85%, while Grand Staircase will be halved. Both National Monuments are in Utah. The decision awaits final congressional approval and comes after an initial report recommended changes to a dozen monuments, including shrinking or opening them to "traditional uses" like mining and timber farming.
Inserted a plan to end restrictions on drilling in the Arctic National Wildlife Refuge into the tax bill
What the rule does: The wildlife refuge designation is part of an initiative begun by President Eisenhower and extended by President Carter that protected 19 million acres of land in northeastern Alaska— a region home to a greater variety of animals and plants than any other protected area in the region.
Current status: A version of the tax bill passed by the Senate in early December includes a provision that would open up part of the refuge to drilling before 2027. Final votes on the bill are expected next week.
What the rule does: UNESCO's key function is designating and protecting official international landmarks, or "world heritage sites." In the US, those include important environmental areas like the Grand Canyon, Glacier Bay, and Redwood national and state parks. The US stopped being a contributing member in 2011, when UNESCO admitted Palestine. (A US law prohibits funding any organization that recognizes the country.)
Current status: Trump's decision to fully withdraw, made public in October, would officially end the US-UNESCO relationship at the end of 2018.