During his first two months in office, President Donald J. Trump has rolled back key Obama-era greenhouse gas regulations. Without these rules in place, the United States is set to fall far short of its 2015 Paris Agreement pledge: to lower emissions by at least 26 percent below 2005 levels by 2025.

Here is how some of President Barack Obama’s signature policies have fared so far under the Trump administration:

Cleaner power plants

Obama-era policies for reducing greenhouse gas emissions 2005 2010 2015 2020 2025 7.0 Business as usual 2016 Clean Power Plan 2009 6.0 Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 Clean Power Plan 2009 6.0 Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 Clean Power Plan 2009 6.0 Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Clean Power Plan Paris goal Gigatons of CO2 equivalent 5.0

In an executive order released Tuesday, Mr. Trump instructed the Environmental Protection Agency to reverse course on the Obama administration’s biggest climate change policy, the Clean Power Plan, which aimed to cut emissions from existing coal- and gas-fired power plants.

If implemented to its fullest extent, the plan would have reduced carbon emissions by nearly 650 megatons by 2025 – just under halfway to the Paris pledge, according to an analysis by Climate Interactive.

Even without federal leadership, state and local initiatives will continue to reduce emissions from power plants, said Doug Vine, Senior Energy Fellow at the Center for Climate and Energy Solutions. “But it’s getting harder to see how we get to 26 percent by 2025,” he said.

More efficient cars

2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Fuel standards (Personal and commercial vehicles) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Fuel standards (Personal and commercial vehicles) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Fuel standards (Personal and commercial vehicles) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Fuel standards Paris goal Gigatons of CO2 equivalent 5.0

Mr. Trump has also taken aim at fuel economy standards that would cut tailpipe CO2 emissions from personal cars and trucks.

Arguing that Obama-era rules burden American automakers, Mr. Trump instructed E.P.A. administrator Scott Pruitt to reopen a review of fuel standards earlier this month. Fuel economy targets are locked in through 2021, but Mr. Pruitt could weaken rules for vehicles manufactured between 2022 and 2025.

The Obama administration also issued fuel efficiency rules for heavy-duty commercial vehicles. So far, Mr. Trump and Mr. Pruitt have not announced plans to weaken those rules.

The transportation sector is now the largest emitter of carbon dioxide in the United States, making fuel standards an important part of reducing CO2 emissions.

Fewer methane emissions

2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Methane and N2O (Oil and gas, landfill and fertilizer use) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Methane and N2O (Oil and gas, landfill and fertilizer use) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Methane and N2O (Oil and gas, landfill and fertilizer use) Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Methane and N2O Paris goal Gigatons of CO2 equivalent 5.0

Reaching the Paris target will be difficult without tighter regulations on methane emissions from the oil and gas industry, said Romany Webb, a climate law fellow at Columbia University. Over a 20-year span, methane traps 86 times as much heat as CO2.

Earlier this month, the E.P.A. announced it was withdrawing a rule that required existing oil and gas well operators to provide information about methane emissions. The rule would have laid the groundwork for future regulations.

In February, House Republicans voted to repeal another Obama-era methane rule, which empowered the Bureau of Land Management to address methane waste from fossil fuel operations on public and tribal lands. The repeal legislation has stalled in the Senate.

Eco-friendlier appliances

2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Energy efficiency and HFCs Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Energy efficiency and HFCs Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Energy efficiency and HFCs Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 Energy efficiency and HFCs Paris goal Gigatons of CO2 equivalent 5.0

As one of its first actions, the Trump White House issued a freeze on all new or pending regulations, which put on hold several Obama-era energy-efficiency standards that cover products like portable air conditioners and commercial boilers. Though these fairly uncontroversial rules have not been officially undone, they remain in regulatory limbo.

The Trump administration does appear to support Obama-era regulations of hydrofluorocarbons, particularly potent greenhouse gases most often used in refrigeration and air conditioning equipment. The rules have the backing of American chemical manufacturers who produce alternatives to HFCs.

California: a climate battle brewing

2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 California Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 California Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 California Paris goal Gigatons of CO2 equivalent 5.0 2005 2010 2015 2020 2025 7.0 Business as usual 2016 2009 6.0 California Paris goal Gigatons of CO2 equivalent 5.0

California policies alone are set to bring national emissions 5 percent of the way to the Paris pledge.

In 2015, the state committed to generating half of its electricity from renewable sources by 2030 and doubling the energy efficiency of existing buildings. The state also collaborated with the Obama administration on fuel economy standards, and it plans to have 1.5 million zero-emissions vehicles on the road by 2025.

But California may be on a collision course with the Trump administration over its vehicle standards.