Levels of air pollutants and warming gases over some cities and regions are showing significant drops as coronavirus impacts work and travel.
Researchers in New York told the BBC their early results showed carbon monoxide mainly from cars had been reduced by nearly 50% compared with last year.
Emissions of the planet-heating gas CO2 have also fallen sharply.
But there are warnings levels could rise rapidly after the pandemic.
With global economic activity ramping down as a result of the coronavirus pandemic, it is hardly surprising that emissions of a variety of gases related to energy and transport would be reduced.
Scientists say that by May, when CO2 emissions are at their peak thanks to the decomposition of leaves, the levels recorded might be the lowest since the financial crisis over a decade ago.
While it is early days, data collected in New York this week suggests that instructions to curb unnecessary travel are having a significant impact.
Traffic levels in the city were estimated to be down 35% compared with a year ago. Emissions of carbon monoxide, mainly due to cars and trucks, have fallen by around 50% for a couple of days this week according to researchers at Columbia University.
They have also found that there was a 5-10% drop in CO2 over New York and a solid drop in methane as well.
“New York has had exceptionally high carbon monoxide numbers for the last year and a half,” said Prof Róisín Commane, from Columbia University, who carried out the New York air monitoring work.
“And this is the cleanest I have ever seen it. It’s is less than half of what we normally see in March.”
Although there are a number of caveats to these findings, they echo the environmental impacts connected to the virus outbreaks in China and in Italy.
An analysis carried out for the climate website Carbon Brief suggested there had been a 25% drop in energy use and emissions in China over a two week period. This is likely to lead to an overall fall of about 1% in China’s carbon emissions this year, experts believe.
Both China and Northern Italy have also recorded significant falls in nitrogen dioxide, which is related to reduced car journeys and industrial activity. The gas is a serious air pollutant and also indirectly contributes to the warming of the planet.