Is cleaner air responsible for recent global warming?
The Observatory
20 Mar 2025
Written By Dr David Whitehouse
Is the clue in the Stratosphere?
Every once in a while, a paper comes along that make you think out of the box, and that’s good. Even if it proves to be unsubstantiated, it is a useful exercise that all scientists should go through from time to time. Carbon dioxide is a greenhouse gas accumulating in our atmosphere, and physics grants it a role in global warming. Climate models predict it causes surface warming and stratospheric cooling.
The overall climatic response is very complex and, in a recent paper, Qing-Bin Lu of Waterloo University in Canada looks at regional and global upper stratosphere temperature (UST) and surface temperature, as well as various climate drivers other than carbon dioxide, including ozone, aerosols, solar variability, snow cover extent, and sea ice extent. It is well known that simulations by mainstream climate models often consider that these shorter-term climate forcings likely cancel out, and warming is pretty much controlled by just carbon dioxide emissions. Accepting that, Lu is clearly thinking outside the box labelled “carbon dioxide”.
Carbon dioxide-based climate models in the IPCC AR6 2 show that although these short-term effective radiative forcings did essentially cancel out during the period 1970–2010, they have more recently led to a positive net forcing of 0.4–0.5 W/m2 from around 2010 up to the present. Lu notes another climatic pattern in addition to the predicted continuous surface warming and upper stratospheric cooling by carbon dioxide-based climate models. The observed data, he maintains, show that the UST at altitudes of 35–40 km demonstrates warming trends in the polar regions but no significant trends in non-polar regions since 2002.
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