July 20 (UPI) -- New analysis of satellite data has revealed the atmospheric signature of seasonal shifts caused by climate change.
Previous studies have revealed seasonal changes on the ground. As the planet has warmed, animal migrations have shifted -- birds are flying south and flowers are blooming earlier and earlier. Sea ice patterns have changed, and both the hurricane and wildfire seasons have grown longer.
For the new study, scientists set out to find similar shifts several miles above Earth's surface. Their effort, which included the analysis of satellite temperature data collected between 1979 and 2016, marked the first time scientists have detected seasonal changes in the atmosphere.
According to their calculations, detailed this week in the journal Science, the chance of such shifts being the product of natural variation -- as opposed to manmade climate change -- is approximately five in a million.
"In the biological world, lots of people have been looking for and finding these changes, so we decided to take a look at the satellite data," lead study author Benjamin Santer, an atmospheric scientist at the Lawrence Livermore National Laboratory in California, told Nature. "What we see is profound evidence of the human impact on climate, not only in the annual temperatures but also in the seasonal cycle."
To pinpoint season atmospheric shifts, scientists used computer models to simulate thousands of years of climate behavior, with and without rising greenhouse gas emissions. Researchers then compared the simulations' predictions with the satellite temperature data collected after 1979.
The satellite data was most similar to the predictions of simulations that included rising greenhouse gas emissions. The most striking difference was found among satellite data recorded above landmasses. Scientists found the difference between summer and winter temperatures have grown by an average of 0.4 degrees Celsius over the last four decades. The difference is mostly explained by an increase in mid-latitude warming during the summer in both hemispheres.
"The changing seasonal cycle provide powerful and novel evidence for a significant human effect on Earth's climate," Santer said in a news release.
More than anything, the findings confirm what climate scientists already knew. But Santer told Nature he hopes the findings will silence climate skeptics who argue evidence of climate change is over-reliant on ground-based measurements.
"I don't think this solves a major problem in atmospheric sciences, nor does it change anything that I think about the climate system," Texas A&M researcher Andy Dessler told Nature. "But it does provide even more evidence that humans are altering the climate."