One of the very few missing pieces left in the jigsaw puzzle of Global Warming has been found, showing that the upper atmosphere is warming as models predict.
The basic physics of how carbon dioxide traps heat has been known since the 19th Century, and evidence that an increase would lead to a warmer planet was presented in the 1930s. Since then, we have been conducting a giant experiment to test the theory.
From melting icepacks and rising sea levels to warmer land and oceans the models' predictions have been repeatedly vindicated. Even a cooler stratosphere, something that would not be seen if the warming was coming from increased solar output, has been very much in evidence. Nevertheless, a few predictions have not been confirmed.
A favorite example for bloggers is the tropospheric hotspot. The troposphere stretches to a height of around 17km (11 miles) and the lower portion has warmed dramatically over the last four decades. Models suggest that there should also be warming in the upper troposphere, 8-17km (5-11 miles) above the surface of the Earth.
Unsurprisingly, we have fewer measurements of the temperature at the top of Mt Everest than at sea level, but there is a substantial dataset of balloon readings going back to the 1950s. These have generally been interpreted as showing less warming than expected, particularly in tropical regions.
Those who deny the evidence for Global Warming tend to exaggerate how much upper troposphere warming we should expect, and therefore the scale of mystery. Nevertheless, climate scientists have been genuinely puzzled.
However, in Environmental Research Letters, Professor Steve Sherwood and Ms Nidhi Nishant of the ARC Centre of Excellence for Climate System Science, Australia, claim that the hotspot has been there all along.
"Using more recent data and better analysis methods we have been able to re-examine the global weather balloon network, known as radiosondes, and have found clear indications of warming in the upper troposphere," Sherwood said in a statement. "We were able to do this by producing a publicly available temperature and wind data set of the upper troposphere extending from 1958-2012, so it is there for anyone to see."
The methodology used is easily replicable. Sherwood describes it as "a well established procedure developed by statisticians in 1977."
The pair also found that the upper troposphere has been warming over recent years, despite deniers' other much hyped warming “pause”.
At the same time, Sherwood found a 10% increase in wind speeds over the Southern Ocean, which may be an effect of ozone depletion. Sherwood thinks that the wind speeds may be contributing to storage of heat within the oceans, rather than the surface.
However, Sherwood's analysis does leave one remaining missing piece. Between 14 and 15km (8.7 and 9.4 miles) above sea level there was no warming trend, while at tropical latitudes it was slightly slower than expected. These will presumably become the new center of attention for everyone telling us that we have nothing to worry about.
