With the dramatic reduction in car traffic and commercial flights, carbon emissions have been falling around the globe. If the slowdown continues, some are estimating the world could see the largest drop in emissions in the last century.

Still, overall greenhouse gas emissions in the atmosphere are still going up and the decline will likely be smaller than what scientists say is necessary to avoid the worst impacts of climate change.

So far, the effects are just starting to appear. In China, the first country to lock down, greenhouse gas emissions dropped an estimated 25% in February as factories and industrial producers slowed output. That decreased coal burning, which has come back slowly since then.

"A month or two of shelter in place will drop carbon dioxide emissions a few percent here or there, but it won’t change the year substantially unless we stay like this for some time," says Rob Jackson, environmental scientist at Stanford University.

The declines are still too small to be read by greenhouse gas observatories around the world, like the one on top of the Mauna Loa volcano in Hawaii, given the natural changes in atmosphere this time of year. Because much of the Earth’s land mass is in the northern hemisphere, plants and forests there cause carbon levels to fluctuate as they bloom in the spring, drawing carbon dioxide from the air.

If countries continue shelter-at-home orders, emissions declines could be greater. The U.S. Energy Information Administration estimates U.S. emissions from gas and energy use could drop more than 7% this year, similar to a 2009 decline during the financial crisis.

Worldwide, early estimates put global emissions dropping around 4%. Still, that’s less than the 7.6% the U.N. says is needed to avoid the worst impacts of climate change by limiting warming to 1.5 degrees Celsius.

To achieve those cuts, scientists say more fundamental changes are needed, like switching to renewable energy.

"This isn’t the way we want to reduce our fossil fuel emissions," says Jackson. "We don’t want tens of millions of people being out of work as a path to decarbonizing our economy. We need systemic change in our energy infrastructure and new green technologies."

Still, Jackson says the recent changes are providing useful insights.

"It’s as if a third of the cars on the road were suddenly electric, running on clean electricity and the air pollution is plummeting," says Jackson. "It’s really a remarkable experiment and it shows the benefits of clean energy."