Wild sheep wandered through deserted business districts in England. Lions lounged on once-busy roadways in Africa.

But if you thought the environment clawed its way back to health during the coronavirus pandemic shut-downs, scientists on Monday provided a reality check: the dip in global greenhouse gas emissions during the heart of the shutdowns, while dramatic, was only a blip.

2020 saw the highest release of atmospheric carbon dioxide since measurements began 63 years ago.

Scientists at Scripps Institution of Oceanography and The National Oceanic and Atmospheric Administration report that levels of atmospheric carbon dioxide peaked in May at nearly 419 parts per million.

The NOAA says those are levels not seen since around 3.6 million years ago, a period known as the Mid-Pliocene Warm Era, when the sea level was about 78 feet higher than today.

The shutdowns offered temporary relief; scientists say carbon emissions dropped by anywhere from 5.8 to 7 percent. Scientists at the International Energy Agency say that is the largest annual percentage decline since World War Two, and it was fueled by a dramatic decline in the demand for oil and coal.

But the human activity -- fossil-fuel burning -- that leads to carbon emissions, came roaring back by the end of 2020 and the Paris-based IEA says global energy demand is now set to surpass 2019 levels.

More consumers and corporations are taking notice: Amazon is vowing to reach at least 50% net carbon zero by 2030. And Delta Airlines is pledging one billion dollars to become the first carbon neutral airline.

It is a welcome, if belated, move, according to the NOAA.

"It's going to take a deliberate focus on reducing fossil fuel emissions to near zero," Colm Sweeny of the NOAA's Global Monitoring Lab said in April. "Even then, we'll need to look for ways to further remove greenhouse gasses from the atmosphere."/aa