From the University of Exeter, comes this statistical prediction that doesn’t seem to be getting a lot of press, and rightly so. Read on.
Future Climate Change Revealed by Current Climate Variations
Uncertainty surrounding the extent of future climate change could be dramatically reduced by studying year-on-year global temperature fluctuations, new research has shown.
A team of scientists from the University of Exeter and the Centre of Ecology and Hydrology has pioneered a new process to reduce uncertainty around climate sensitivity – the expected long-term global warming if atmospheric carbon dioxide is stabilised at double pre-industrial levels.
While the standard ‘likely’ range of climate sensitivity has remained at 1.5-4.5°C for the last 25 years the new study, published in leading scientific journal Nature, has reduced this range by around 60 per cent.
The research team believe that by dramatically reducing the range of climate sensitivity, scientists will be able to have a much more accurate picture of long-term changes to the Earth climate.
Lead-author Professor Peter Cox 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”.
The new research made their breakthrough by moving their focus away from global warming trends to date, and instead studying variations in yearly 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, carried out the calculations to work-out a measure of temperature fluctuations that reveals climate sensitivity.
This metric of temperature fluctuations can also be estimated from climate observations, allowing the model line and the observations to be combined to estimate climate sensitivity.
Using this approach, the team derive a range of climate sensitivity to doubling carbon dioxide of 2.8+/-0.6°C, which reduces the standard uncertainty in climate sensitivity (of 1.5-4.5°C) by around 60%.
Mark said: “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”.
Explaining the significance 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 research was supported by the European Research Council (‘ECCLES’ project), the EU Horizon 2020 Programme (‘CRESCENDO’ project), and the UK’s Natural Environment Research Council.
The paper: https://www.nature.com/articles/nature25450
Emergent constraint on equilibrium climate sensitivity from global temperature variability
Equilibrium climate sensitivity (ECS) remains one of the most important unknowns in climate change science. ECS is defined as the global mean warming that would occur if the atmospheric carbon dioxide (CO2) concentration were instantly doubled and the climate were then brought to equilibrium with that new level of CO2. Despite its rather idealized definition, ECS has continuing relevance for international climate change agreements, which are often framed in terms of stabilization of global warming relative to the pre-industrial climate. However, the ‘likely’ range of ECS as stated by the Intergovernmental Panel on Climate Change (IPCC) has remained at 1.5–4.5 degrees Celsius for more than 25 years1. The possibility of a value of ECS towards the upper end of this range reduces the feasibility of avoiding 2 degrees Celsius of global warming, as required by the Paris Agreement. Here we present a new emergent constraint on ECS that yields a central estimate of 2.8 degrees Celsius with 66 per cent confidence limits (equivalent to the IPCC ‘likely’ range) of 2.2–3.4 degrees Celsius. Our approach is to focus on the variability of temperature about long-term historical warming, rather than on the warming trend itself. We use an ensemble of climate models to define an emergent relationship2between ECS and a theoretically informed metric of global temperature variability. This metric of variability can also be calculated from observational records of global warming3, which enables tighter constraints to be placed on ECS, reducing the probability of ECS being less than 1.5 degrees Celsius to less than 3 per cent, and the probability of ECS exceeding 4.5 degrees Celsius to less than 1 per cent.
Here’s how I see it: