Researchers have developed a new approach which significantly reduces uncertainty regarding measuring future increases to the water vapour in the stratosphere, increases which risk amplifying climate change impacts and slowing down the ozone layer recovery.
The approach functions on statistical learning and combines satellite data with climate models to predict more accurately the future water vapour amounts in the stratosphere, an extremely dry region of the Earth's atmosphere 1550 km above the surface, the international team of researchers led by the University of East Anglia (UEA), UK, said.
"Man-made climate change affects Earth's atmosphere in many important and often surprising ways," said Peer Nowack, until recently a member of the Climatic Research Unit at UEA and now at the Institute of Theoretical Informatics at the Karlsruhe Institute of Technology, Germany.
"In our paper, we look at changes in stratospheric water vapour under global warming, an effect that is still poorly understood. Since water vapour is central to the physics and chemistry of the stratosphere, I felt that we crucially need a new approach to address this longstanding uncertainty factor," said Nowack.
One of the key results of this research, published in the journal Nature Geoscience, represented a 50 per cent reduction in the water vapour concentrations in the stratosphere in almost 95 per cent of climate model responses.
The research thus, ruled out the most extreme scenarios which say that water vapour concentrations could increase by more than 25 per cent per degree of global warming.
"With this approach, we were able to show that many climate model projections of very large stratospheric water vapour changes are now inconsistent with observational evidence," said co-author Sean Davis, a Research Scientist at the National Oceanic and Atmospheric Administration (NOAA) in the US, specialising in satellite measurements of stratospheric water vapour.
The amount of water vapour that the stratosphere holds is one of the so-called climate feedbacks, which are processes that stand to either amplify or dampen global warming.
These feedbacks further add to the complexity of understanding the underlying processes that control stratospheric water vapour and thus, present a challenge to quantifying stratospheric water vapour trends under global warming.
While climate models have predicted these vapour amounts to increase, the range of modelled increases has remained very wide for decades.
However, Manoj Joshi, professor of Climate Dynamics at UEA and a co-author on the paper, said, "Our research implies that while stratospheric water vapour concentrations are still likely to increase with global warming, the large changes that could substantially delay ozone recovery are highly unlikely."
