The lowest level of the atmosphere, called the troposphere, has been growing warmer and gaining thickness at a rate of 53 metres per decade since 2000
The tropopause – a boundary within the atmosphere – is increasing in altitude due to climate change.
The lowest layer of the atmosphere where we live and breathe is called the troposphere, and it is separated from the stratosphere above – which is where the protective ozone layer sits – by the tropopause.
There is natural variation in the altitude of the tropopause: it lies roughly 18 kilometres above sea level at the equator and around 10 kilometres above sea level at the poles.
But Jane Liu at the University of Toronto in Canada and her colleagues have found that its altitude across the northern hemisphere has risen in recent decades.
The researchers analysed atmospheric data such as pressure, temperature and humidity collected by weather balloons, and also used data from GPS satellites, to track changes in the tropopause between 1980 and 2020. The team focused specifically on the northern hemisphere, where changes to tropopause height are thought to have been larger than in the southern hemisphere.
The team found that the altitude of the tropopause in the northern hemisphere has steadily increased between 1980 and 2020. Between 2001 and 2020, the altitude increased at a rate of around 53.3 metres per decade, which is a slightly higher rate of increase than between 1980 and 2000.
This increase excludes any impact of natural climate variations, such as volcanic eruptions and the El Niño-Southern Oscillation, which were factored out, and so is due to climate change alone, according to the researchers.
They suggest warming of the troposphere due to its increasing concentration of greenhouse gases is expanding this layer, driving the tropopause to greater altitudes. An additional, less significant driving force is that the stratosphere has decreased in volume due – somewhat counterintuitively – to cooling of this layer induced by, for instance, ozone deterioration.
“The increase in tropopause height is a sensitive indicator for anthropogenic climate change,” says Liu.
The change in the tropopause height may influence our climate and weather circulation, although there are very few studies that investigate these impacts in detail, says Liu.
“Our work tells us human activity induced climate change can make a difference to many aspects of our daily lives,” says Liu. “Now we see it… in changes to our tropopause height.”
“The study exploits highly detailed observation data sets to quantify changes in the tropopause in unprecedented detail,” says Amanda Maycock at the University of Leeds in the UK. “Overall, the study provides further evidence that the impacts of climate change are evident in every region of the atmosphere.”
Journal reference: Science Advances, DOI: 10.1126/sciadv.abi8065
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