This contraction means the upper atmosphere becomes less dense, which in turn reduces drag on satellites and other low-orbit objects — by about a third by 2070, calculates Ingrid Cnossen, a research fellow at the British Antarctic Survey.
On the face of it, this is good news for satellite operators. Their payloads should remain operational longer before falling back to Earth. But the problem is the other objects that share these heights. The growing amount of space junk — all sorts of equipment left in orbit — also lingers longer, increasing the risk of collisions with currently operational satellites.
More than 5,000 active and defunct satellites, including the International Space Station, are in orbit at these altitudes, accompanied by more than 30,000 known pieces of debris over 4 inches in diameter. The risks of collisions, says Cnossen, will continue to increase as cooling and contraction accelerate.
This may be bad for space agency business, but how will the changes in the sky affect our world below?
A major concern is the already fragile state of the ozone layer in the lower stratosphere, which protects us from harmful solar radiation that causes skin cancer. For much of the 20th century, the ozone layer thinned due to industrial emissions of ozone-eating chemicals such as chlorofluorocarbons (CFCs). Outright ozone holes formed around Antarctica every spring.
The 1987 Montreal Protocol aimed to close the annual gaps by eliminating those emissions. But it’s now clear that another factor is undermining this effort: stratospheric cooling.
Ozone destruction works in overdrive in polar stratospheric clouds, which only form at very low temperatures, particularly over polar regions in winter. But the cooler stratosphere has led to more occasions for such clouds to form. While the ozone layer over Antarctica is slowly recovering as CFCs disappear, the Arctic appears to be different, says Peter von der Gathen of the Alfred Wegener Institute for Polar and Marine Research in Potsdam, Germany. In the Arctic, cooling exacerbates ozone loss. Von der Gathen says the reason for this difference is not clear.
In the spring of 2020, the Arctic had its first full ozone hole with more than half of the ozone layer lost in some places, which Von der Gathen blames on rising CO2 concentrations. It could be the first of many. In a recent paper in Nature communication, he warned that the continued cooling means that current expectations that the ozone layer will be fully healed by mid-century are almost certainly overly optimistic. As for current trends, he said, “conditions favorable to a large seasonal loss of ozone in the Arctic column may persist or even worsen into the end of this century … much longer than generally believed.”
This is more concerning because, while the regions under previous Antarctic holes were largely devoid of humans, the regions under future Arctic ozone holes may be some of the most densely populated in the world, including central and western Europe. If we thought the thinning ozone layer was a 20th century concern, maybe we should think again.