It’s well known that tropospheric warming causes stratospheric cooling, but somehow the BBC, Guardian, and New York Times don’t seem to know that:
A huge hole that appeared in the Earth’s protective ozone layer above the Arctic in 2011 was the largest recorded in the northern hemisphere, though the sudden appearance of the hole was not due to man-made causes, scientists said in a report on Monday….man-made chemicals such as chlorofluorocarbons (CFCs) destroy ozone in the stratosphere, after sunlight breaks up the complex chemicals into simpler forms that react with ozone. While some of the chemicals are covered by a UN treaty that aims to stop their use, it will be decades before they are fully phased out of production.
You don’t need a PhD in climatology to understand that either the journalist who wrote this in the Guardian or the research team itself has not only buried the lede, but denied it. While the “sudden appearance” of the hole might be explicable solely through reference to proximate causes intrinsic to the atmosphere itself (eg. strengthening of the polar vortex), make no mistake: anthropogenic global warming of the troposphere (the lowest layer of the atmosphere) is damaging to the stratospheric ozone layer.
This simple connection is the most relevant fact for journalists or scientists to widely communicate, whether to policymakers or the public. But it isn’t mentioned anywhere in the article in the Guardian nor in the BBC synopsis, and I had trouble finding it in the extensive research paper in Nature as well. It’s certainly not in their abstract.
Meteorologist Jeff Masters explains these atmospheric dynamics simply and well, something the journalists and climatologists found it strangely difficult to do:
The recovery of the ozone layer is being delayed by human emissions of greenhouse gases like carbon dioxide and methane. These gases trap heat near the surface, but cause cooling of the stratosphere and increased formation of the [polar stratospheric clouds] that help destroy ozone. We need only look as far as our sister planet, Venus, to see an example of how the greenhouse effect warms the surface but cools the upper atmosphere. Venus’s atmosphere is 96.5% carbon dioxide, which has triggered a hellish run-away greenhouse effect. The average surface temperature on Venus is a sizzling 894 °F, hot enough to melt lead. Venus’s upper atmosphere, though, is a startling 4 – 5 times colder than Earth’s upper atmosphere. The explanation of this greenhouse gas-caused surface heating and upper air cooling is not simple, but good discussions can be found at Max Planck Institute for Chemistry and realclimate.org, for those unafraid of radiative transfer theory.
One way to think about the problem is that the amount of infrared heat energy radiated out to space by a planet is roughly equal to the amount of solar energy it receives from the sun. If the surface atmosphere warms, there must be compensating cooling elsewhere in the atmosphere in order to keep the amount of heat given off by the planet the same and balanced. As emissions of greenhouse gases continue to rise, their cooling effect on the stratosphere will increase. This will make recovery of the stratospheric ozone layer much slower.
I must add that the New York Times, in covering this story, went one step further than the Guardian and BBC by explicitly calling into doubt the well-known connection between tropospheric warming and stratospheric cooling through an interview with a NASA scientist:
In a telephone interview, Dr. Santee [a planetary scientist at NASA’s Jet Propulsion Laboratory] and a NASA laboratory colleague and co-author, Nathaniel J. Livesey, were nonetheless cautious about linking the cold temperatures in the upper atmosphere far north to the warmer weather that has been unfolding closer to the earth’s surface. That warming trend led to one of the greatest-ever reductions in the extent of Arctic sea ice this year.
Whether the cold snap in the stratosphere “is related to it being warmer than it typically is lower down is intriguing,” Dr. Livesey said, “but the connection has yet to be made.”