Recent research has proved that uncertainty surrounding the extent of future climate change can be intensely decreased by studying year-on-year global temperature fluctuations.
A team of scientists from the University of Exeter and the Centre of Ecology and Hydrology has now established a new process for reducing uncertainty surrounding climate sensitivity – the anticipated long-term global warming if atmospheric carbon dioxide is stabilized at double pre-industrial levels.
While the typical ‘likely’ range of climate sensitivity has continued to be at 1.5-4.5 oC for the last 25 years, the new study, published in a principal scientific journal Nature, has decreased this range by almost 60%.
The research team believes that dramatically lowering the range of climate sensitivity will allow scientists to have a much more perfect picture of long-term modifications to the Earth climate.
Professor Peter Cox, lead-author, from the University of Exeter said: “You can think of global warming as the stretching of a spring as we hang weights from it, and climate sensitivity as related to the strength of the spring”.
“To relate the observed global warming to climate sensitivity you need to know the amount of weight being added to the spring, which climate scientists call the ‘forcing’, and also how quickly the spring responds to added weight. Unfortunately, we know neither of these things very well”.
With this new research, the researchers were able to make their breakthrough by shifting their focus away from global warming trends to date, and instead studying differences in annual global temperatures.
Co-author Professor Chris Huntingford, from the Centre for Ecology and Hydrology, explained: “Much of climate science is about checking for general trends in data and comparing these to climate model outputs, but year-to-year variations can tell us a lot about longer-term changes we can expect in a physical system such as Earth’s climate.”
Mark Williamson, co-author of the study and a postdoctoral researcher at the University of Exeter, performed the calculations in order to execute a measure of temperature fluctuations that exposes climate sensitivity.
It is also possible to estimate this metric of temperature fluctuations from climate observations, permitting the observations and the model line to be merged in order to estimate climate sensitivity.
With this approach, the team was able to develop a range of climate sensitivity and also succeeded in doubling carbon dioxide of 2.8+/-0.6 oC, which decreases the typical uncertainty in climate sensitivity (of 1.5-4.5 oC) by around 60%.
We used the simplest model of how the global temperature varies, to derive an equation relating the timescale and size of the fluctuations in global temperature to the climate sensitivity. We were delighted to find that the most complex climate models fitted around that theoretical line.
Mark Williamson, Co-Author
Elucidating the importance of the results, Professor Cox added: “Our study all but rules-out very low or very high climate sensitivities, so we now know much better what we need to. Climate sensitivity is high enough to demand action, but not so high that it is too late to avoid dangerous global climate change”.
The European Research Council (‘ECCLES’ project), the EU Horizon 2020 Program (‘CRESCENDO’ project), and the UK’s Natural Environment Research Council supported the research.