The lower atmosphere is warming while the upper atmosphere is cooling – a clear fingerprint of the enhanced greenhouse effect from human emissions of carbon dioxide.
The simple explanation is that some of the infrared radiation emitted by the surface, which would have normally reached the upper atmosphere, is absorbed by greenhouse gases in the lower atmosphere. The upper atmosphere therefore receives less energy than before, and so cools. The very warm years (intense reds) in the upper atmosphere are the 1982-83 El Chichón and 1991-92 Pinatubo eruptions respectively.
Is the simple explanation correct? The infrared radiation emitted by the surface is not absorbed and re-emitted many times until it reaches a height where the concentration of greenhouse gases is so low that it can escape to space. For most wavelengths this is around 5 km. More greenhouse gases increase the height and given the lapse rate warm the atmosphere. However, in the 15μm band the absorption is so strong that it only escapes to space in the stratosphere. Here the lapse rate is negative, so an increase in greenhouse gases gives cooling.
Thanks for the clarification Geert Jan!
Great picture. Many thanks, Ed.
Yes, but the climate models are still a poor match with the empirical temperature regardless. The models only temporarily resemble the empirical temperature data during the peak of a large El Nino, whereas the rest of the time an embarrassing ‘hiatus’ (IPCC) suggest the temperature could drop out the bottom of the climate models projections:
http://blogs.reading.ac.uk/climate-lab-book/files/2014/01/fig-nearterm_all_UPDATE_2018-panela-1.png
The models are inaccurate, as are the predictions associated with them (i.e. extreme weather, accelerating sea level rise, etc.).
We’ll have to agree to disagree.
Cooling in the lower stratosphere is largely controlled by ozone levels. For example, Thompson and Solomon (2008) write:
http://www.atmos.colostate.edu/~davet/ao/ThompsonPapers/ThompsonSolomon_JClimate2008_InPress.pdf
“The lower stratosphere has cooled by a globally averaged ~0.3-0.5 K/decade since 1979. The global-mean cooling has not occurred monotonically, but rather is manifested as two downward “steps” in temperature, both of which are coincident with the cessation of transient warming after the major volcanic eruptions of El Chichon and Mt. Pinatubo.
“The lower stratosphere has not noticeably cooled since 1995, which indicates that the trends in this region are not dominantly controlled by the known increases in carbon dioxide over this period. Attribution experiments indicate that the long-term cooling in global-mean lower stratospheric temperatures is driven mainly by changes in stratospheric ozone.”
Ozone forcing is several times larger than that from increasing GHGs. From Polvani and Solomon (2012)
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012JD017719
“Confirming and extending earlier studies we find that, over the second half of the 20th century, the model’s lower-stratospheric cooling caused by ozone depletion is several times larger than that induced by increasing greenhouse gases.”
If you run a trend analysis of the lower stratosphere temps since 1994 (after the Pinatubo drop) you find there is no statistically significant cooling trend over the last quarter century.
Thanks for the links to those papers – interesting.
Have added the higher level data from RSS, which also shows a sharp cooling trend too, but this has not been updated recently.