United States greenhouse gas emissions dropped by a record 10.3% last year, the largest annual decline since World War II, according to a new report. But this was mostly owed to the coronavirus pandemic and not because of any significant climate action — which means the US still has a long way to go to get its emissions under control.

The report by the Rhodium Group said the emissions decline in the US last year outpaced the Great Recession of 2009 when emissions dipped 6.3%. They attributed this to behavioral changes associated with the pandemic and warned emissions would go back to their usual growing path this year unless policymakers act.

“We’re seeing things we haven’t seen before, but it’s not for the right reasons,” Hannah Pitt, a senior analyst on Rhodium’s climate and energy team, told Scientific American. “In order to be on track for sustained reductions, there have to be structural changes to the underlying drivers of emissions.”

Before the pandemic, US emissions had been on a very slow decline since 2005, mainly because energy companies have been shifting away from coal to natural gas and renewable energy. Hundreds of coal power plants have closed down over the past decade despite the efforts of President Donald Trump to revive the sector. However, although some of that is now covered by renewables, natural gas has become the king of US energy.

But then the coronavirus pandemic arrived, with several governors putting their states under lockdown and many Americans staying home as much as possible. This took down emissions across sectors of the economy that had rarely seen sustained drops before, such as transportation, the main source of emissions in the country.

The sector saw a 14.7% drop in emissions last year, according to the new report, as people stopped driving to work and airlines cancelled flights. This continued even when states relaxed their lockdowns in the second part of the year. Americans drove 15% fewer miles in 2020 compared to 2019, with demand for jet fuel one-third down.

Emissions from heavy industries such as cement also dropped 7%, with automakers and manufacturers producing fewer goods amid the economic drop. Buildings across the US, which produce carbon dioxide when they burn oil or natural gas for heat, saw emissions fall 6.2% thanks to the state’s lockdowns and the warmer weather.

Meanwhile, in the electricity sector, emissions plunged 10.3% last year thanks to a significant drop in coal burning. Electricity demand was lower than usual and energy companies used their coal plants less often. Instead, they used more natural gas, which produces less carbon dioxide, as well as more solar and wind power.

It was a big year for renewable energy in the US, with many energy companies building a record number of wind farms and solar plants ahead of a deadline to claim a federal tax credit. Rhodium estimates that the US produced as much electricity from renewables last year as it did from coal, something never seen before.

The overall emissions drop puts the US close to achieving one of its major climate change goals under the Paris Agreement. Former President Barack Obama had pledged that the US emissions would drop 17% below 2005 levels by 2020. President Trump then decided to exit the pact amid an overall rollback on environmental regulations.

Still, the report has a few limitations. Rhodium’s numbers don’t incorporate any rise in emissions resulting for them the record wildfires in the West, which burned millions of hectares of forests and grassland. An estimate from BloombergNEF said wildfires could offset about 3% of the drop in emissions from energy and industry.

The other potential problem is that the US emissions could go back up once vaccines are massively distributed and the economy recovers. Rhoidum said that a similar rebound happened after the financial crisis of 2008 and 2009, which caused emissions to drop. Some sectors such as air travel and steel production are already rebounding in the US.

The Global Carbon Project had already estimated that emissions decreased by around 7% globally last year. While this might look like something significant, it actually doesn’t make much of a difference to climate change. Greenhouse gases remain in the atmosphere for centuries so climate action has to be maintained every year.

Under the Paris Agreement, countries agreed to limit global warming to below 2ºC above pre-industrial levels, and to pursue efforts to limit it to 1.5ºC. Still, for this to happen, emissions have to drop significantly. With the current climate pledges by countries, the world is heading to a temperature increase between 3º C and 4ºC, and the US has more than contributed its share.