Carbon dioxide (CO2) emissions dropped by 7% this year, the biggest annual drop ever recorded since World War II, as most countries imposed lockdowns and restrictions to limit the spread of the novel coronavirus.

Still, this isn’t the way to deal with climate change. Emissions are likely to rebound next year, and experts are calling for a sustainable and drastic cut to emissions, not a one-time accident.

The coronavirus pandemic led to a decline in emissions of 2.4 billion metric tons of carbon dioxide, according to the annual assessment of the Global Carbon Project. This was much more significant than other drops in recent history, such as the end of World War Two (0.9 billion metric tons) or the global financial crisis in 2009 (0.5 billion tons)

“Of course, lockdown is absolutely not the way to tackle climate change,” Corinne LeQuere, a climate scientist at the University of East Anglia, who participated in the study, said in a statement.

Researchers said the drop was mainly because people were staying indoors, working from home and traveling less by car and plane. Transportation accounted for the largest share of the global decline in emissions this year. Still, LeQuere and colleagues argued, emissions will go back to business-as-usual as soon as the pandemic end is in sight — or maybe even above that, to make up for lost time.

In April, when the first wave of the pandemic was at its peak, emissions from road transport fell by half. Then, by December, they had fallen 10% year-on-year. Emissions from aviation were also down 40% this year, while emissions from industrial activity, accounting for 22% of the total, were down by 30% in most countries. The largest declines in emissions were registered in the US and in the European Union, down 12% and 11% respectively. China, on the other hand, saw a 1.7% decline as it had an earlier lockdown with less of a second wave. Also, China’s emissions are more from the industrial sector, less affected than transportation in the pandemic.

Under the Paris Agreement on climate change, signed five years ago, countries need to cut one to two billion metric tons per year this decade to limit global warming from rising below 2ºC – the goal set in the climate deal. Still, since it was signed in 2015, emissions have only gone up, a trend only now interrupted by the pandemic.

Countries would have to collectively increase their climate action threefold to be in line with the 2ºC goal of the Paris Agreement, according to United Nations estimations. The world is now heading to global warming of about 3ºC based on the country’s climate pledges, which are due to be updated in the next few months.

Philippe Ciais, a researcher at France’s Laboratory of Climate and Environment Sciences, told Deutsche Welle that without the pandemic, the carbon footprint of the largest emitters would have continued to grow this year. The way to address climate change is by speeding up the transition to low-carbon energy, he added, and finding ways to reduce our emissions sustainably.

The researchers from the Global Carbon Project agreed that a rebound of emissions next year is almost certain. Still, to minimize the effect, they are calling countries for a green rather than a brown response to the pandemic. This means funding should be spent only on sustainable projects instead of fossil fuels.

Chris Field, director of the Stanford Woods Institute for the Environment, said in a statement he remained optimistic, as people might have learned lessons amid the pandemic that could decrease emissions. We might see in the future emissions declines related to behavior changes, such as more people working from home, he argued.

This year’s findings of the Global Carbon Project were published in the journal Earth System Science Data.