In all the discussions about climate change, one thing is often overlooked – the upper atmosphere of Earth is actually cooling while the lower atmosphere grows warmer, and this strange paradox is a clear fingerprint of greenhouse gases at work.
Carbon dioxide in the lower atmosphere helps trap heat from the sun’s solar energy reflected off the Earth’s surface and so, like a greenhouse, the lower atmosphere grows warmer. But at high altitudes it is a different story, because the upper atmosphere is so thin that the carbon dioxide releases its energy into space and so the upper atmosphere cools. And that cooling is also making the upper atmosphere contract.
Past studies have shown that the cooling trend is driven by greenhouse gases, as well as shifts in the Earth’s magnetic field and the roughly 11-year cycle in the sun’s solar activity. A recent study disentangled these different factors by simulating the upper atmosphere at 100-500km altitude from 1950 to 2015. The results confirmed that rising carbon dioxide levels were the main driving force cooling the upper atmosphere. Shifts in the Earth’s magnetic field and variations in the solar cycle played much smaller roles.
