A study in the journal Science has found that humans are having a direct effect on Earth’s atmosphere in a way not seen before.
Specifically, scientists led by the Lawrence Livermore National Laboratory (LLNL) in California found that humanity appears to be leaving a “fingerprint” on the planet’s seasons. The temperatures of each season are being directly affected.
Studying the troposphere, which extends up to 16 kilometers (10 miles) above the tropics and 13 kilometers (8 miles) above the poles, they found a global-mean annual average warming of 0.7°C (1.25°F) from 1979 to 2016. And the culprit appears to be humans.
“Our results suggest that attribution studies with the changing seasonal cycle provide powerful and novel evidence for a significant human effect on Earth’s climate,” said LLNL climate scientist and lead author Benjamin Santer in a statement.
The team, which The Guardian describes as “the best of the best climate scientists studying Earth’s atmosphere,” used temperature measurements from satellites to make their findings. They then used computer models of the climate based on greenhouse gas emissions from humans, checked against a model with no human influence.
The results showed a fingerprint of human-caused global warming in the troposphere that could not be accounted for by natural climate variability. A consequence is that the “heartbeat” of seasons, namely the shift from cold winters to hot summers in the Northern Hemisphere, is becoming stronger.
One of the changes seen is that in mid-latitudes in the Northern Hemisphere, the summer is getting warmer faster than the winter. They say this may be due to the large amount of land in the Northern Hemisphere, which is drier in the summer. The same effect wasn’t as apparent in the Southern Hemisphere because it consists more of water.
At the poles, something more unnerving was happening: the seasons seemed to be disappearing entirely. As ice melts and more water is unearthed, the temperature variations between seasons seem to be diminishing.
The report comes as countries around the world, including the UK and Japan, are experiencing wild heatwaves. Humanity’s effect on the climate has been well documented – but now it appears it is having other unseen effects on the atmosphere, too.
“The piling on of evidence is worrying me,” Santer told Bloomberg. “This is the kind of stuff you don’t want to be right about.”