An increase in CO2 could be one reason why a layer of Earth's upper atmosphere went through its biggest contraction in 43 years.
Earth's thermosphere went through its biggest contraction in 43 years.
Researchers expected to see a contraction due to a solar minimum, but not this significant.
One explanation may be an increase in carbon dioxide in the atmosphere.
Scientists are mulling over why part of the Earth's atmosphere recently suffered its biggest collapse since records began, and is only now starting to rebound.
The collapse occurred in a region known as the thermosphere, a rarefied layer of the planet's upper atmosphere between 90 and 600 kilometers (56 to 373 miles) above the surface, which shields us from the sun's far and extreme ultra violet (EUV) radiation.
A report in Geophysical Research Letters by a team led by John Emmert from the United States Naval Research Laboratory has found that the thermosphere went through its biggest contraction in 43 years.
The thermosphere usually expands and contracts in line with the sun's 11-year solar cycle. During solar maximum when solar activity increases, it causes the thermosphere to heat up -- reaching temperatures of 1100°C -- and expand like a marshmallow in a camp fire. The opposite happens during solar minimum.