Dive Brief:

• The White House signaled last week it will not defend Obama-era smog restrictions in an ongoing case at the U.S. Court of Appeals for the District of Columbia Circuit.
• The U.S. Environmental Protection Agency has asked the D.C. Circuit to postpone oral arguments slated for next week, allowing it time to "fully review" the rules. The limits were passed in 2015 to tighten standards on ozone — a main ingredient in smog — from 75 parts per billion (ppb), to 70 ppb. 
• Also last week, nearly two dozen senators have sent a letter to EPA Administrator Scott Pruitt, demanding the agency explain how it intends to address greenhouse gas emissions as it reviews the Clean Power Plan, President Obama's signature carbon regulation. 

Dive Insight:

Stricter smog standards put in place under President Obama now appear to be in danger, along with other climate protections and energy restrictions. President Trump continues working to roll back his predecessor's environmental legacy, alarming some lawmakers who want to ensure the EPA is fulfilling its mission.

Ozone rules were updated in 2015 after the EPA reviewed research linking smog exposure to adverse health effects like asthma. Generators and business groups, however, argue the stricter rules limit economic growth. 

In a court filing last week, the federal government said that “at this time, EPA officials appointed by the new Administration are closely reviewing the 2015 Rule to determine whether the Agency should reconsider the rule or some part of it.”

That is language similar to an executive order issues last month, directing the EPA to review the Clean Power Plan and other greenhouse gas regulations for the power sector. The order also called for the elimination of restrictions on federal coal leasing and reconsideration of rules governing methane regulations and the federal government's use of the social cost of carbon.

But while President Trump vowed to eliminate the Clean Power Plan, which aims to cut emissions from existing power plants 32% by 2030, climate hawks say the EPA is obligated to regulate carbon emissions and they worry the agency will shirk that duty if the rule is rolled back entirely.

In their letter last week, senators asked the White House for more information on the president's executive orders on climate, and also asked "how the agency intends to meet its legal obligations to address carbon pollution emissions if the Clean Power Plan is rescinded."

23 Senators signed the bill, led by Sen. Tom Carper (D-DE).

The letter comes amid uncertainty over the White House's legal strategy to unwind Obama's climate regulations. If the EPA does not seek to replace the Clean Power Plan with another regulatory package, it could open up a legal fight over the agency's 2009 endangerment finding on carbon and the agency's responsibility to regulate the pollutant under the Clean Air Act.