Why is the troposphere the densest layer

The stratosphere has shrunk 400 meters in 40 years

Category Innovation & Technology - 4 days ago

In the past 40 years, the second layer of the atmosphere has narrowed by almost half a kilometer, which could also be potentially dangerous for satellites and GPS.

The worldwide emission of greenhouse gases not only has serious consequences for global temperatures, but also changes the earth's atmosphere itself. Its second layer, the stratosphere, which begins at around 20 kilometers above sea level, is shrinking noticeably. This is the result of an international team of researchers.

This is how thin the earth's protective shield is: the atmosphere, captured by the ISS. © NASA

In the past 40 years, the stratosphere has become 400 meters thinner - every decade by around 100 meters, the experts write 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," said study author Ulrich Foelsche from the University of Graz to the German news magazine SPIEGEL. "This expands as a result, and the boundary to the stratosphere shifts upwards."

Climate change indicator

For the researchers, the shift in atmospheric boundaries is an indicator of man-made climate change. Scientists call tropopause: inside the sharp boundary that separates the lowest layer of the atmosphere from the almost immobile stratosphere above it. It is about nine kilometers above the earth's poles, and about 18 kilometers from the surface of the earth near the equator.

© Petr Pisoft et al 2021

According to the study, 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, were damaging to the ozone layer. Since the ban on CFCs in the Montreal Treaty of 1989, the ozone hole has been closing again.

Silver-blue clouds glow in the twilight, plus the orange troposphere, the lowest and densest part of the earth's atmosphere. © NASA

“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."

The shifting of the layers, the contraction of the stratosphere, is also a clear indicator that the effects are anthropogenic and that the sun is not responsible, as some crude climate crisis hypotheses suggest. “Would be the sun fault With climate change, the stratopause - that is, the upper limit of the layer - would shift systematically upwards and not downwards, ”says Foelsche.

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.

Impact on GPS & Space Debris

Researchers observed the shift in the stratosphere for the first time around 20 years ago and at that time attributed this to solar activity or volcanic eruptions in addition to the emission of greenhouse gases or aerosols.

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 debris would also stay in the atmosphere longer.