NASA image of the atmosphere at an altitude of around 350 kilometers
Photo: Space Frontiers / Getty Images
The emission of greenhouse gases not only has serious consequences for global temperatures, but also changes the earth's atmosphere itself. The second layer, which begins at around 20 kilometers above sea level, is shrinking noticeably.
This is the result of an international team of researchers.
In the past 40 years, the stratosphere has become 400 meters thinner - about 100 meters every decade, write the experts in the journal "Environmental Research Letters".
The near-earth troposphere has expanded upwards, while the stratosphere above has condensed at the same time.
By 2080, the approximately 30-kilometer-thick stratosphere could become another kilometer thinner.
"It is now clear that we are not only warming the earth's surface through man-made greenhouse gas emissions, but also the troposphere," explains study author Ulrich Foelsche from the University of Graz to SPIEGEL.
"This expands as a result, and the boundary to the stratosphere shifts upwards."
Tropopause as a climate change indicator
For the researchers, the shift in atmospheric boundaries is an indicator of man-made climate change.
Scientists call tropopause the sharp boundary that separates the lowest layer of the atmosphere from the almost immobile stratosphere above it.
It is around nine kilometers above the earth's poles, and around 18 kilometers from the surface of the earth near the equator.
The troposphere is warming and pushing up
Photo: Petr Pisoft
According to the researchers, the shrinking stratosphere is coming under pressure from two sides. The troposphere below pushes upwards, and at the same time the stratosphere condenses. "The greenhouse gases not only absorb infrared radiation, they also emit it," says Foelsche. In the upper layers of the atmosphere, this leads to more heat being given off. This cooled them down - and pulled them together.
The thinning of the ozone layer also played a role in this.
The less ozone there is in the stratosphere, the less it can absorb UV radiation from the sun - and thereby heat the air layer.
In the 1970s, it was found that chlorofluorocarbons (CFCs), which were previously used as refrigerants or propellants, depressed the ozone layer.
Since the ban on CFCs in the Montreal Treaty of 1989, the ozone hole has been closing again.
“But we were able to show that the influence of greenhouse gases dominates,” says Foelsche.
"That's why the process will continue even if the ozone layer recovers."
Indicator of human influence
The shifting of the layers is also a strong argument against crude climate change theories that make the sun responsible for climate change.
"If the sun were 'to blame' for climate change, the stratopause - that is, the upper limit of the layer - would be systematically shifted up and not down," says Foelsche.
The »stratospheric contraction« is a clear indicator that the effects are anthropogenic.
Humans change the atmosphere and its natural balance to protect the planet
Photo: Modelist / imago images / Modelist
Eight research institutions in five countries worked together for the new study.
They calculated the shrinkage using, among other things, complex atmospheric and climate models as well as satellite observations since the 1980s.
Researchers observed the shift in the stratosphere for the first time around 20 years ago and at that time attributed this not only to the emission of greenhouse gases or aerosols but also to solar activity or volcanic eruptions.
More space junk
The effects of the shrinking stratosphere on satellites and GPS still have to be investigated in more detail.
The changes could affect the accuracy of global positioning systems such as GPS or Galileo.
It is also possible that the movement in the layers has long-term consequences for the transmission of radio signals.
"If the upper layers of the atmosphere are less extensive, this means that the lifespan of low-flying satellites is systematically extended," says Foelsche. At the same time, the space junk would also stay in the atmosphere longer.