WUWT readers may recall this chart which clearly illustrates just how uncertain climate science really is.
It seems that some climate academics are a bit embarrassed that they haven’t been able to pin down climate sensitivity. From EU Horizon Magazine
Climate sensitivity – reducing the uncertainty of uncertainty
by Jon Cartwright
A study published in January 2018 claims to halve the uncertainty around how much our planet’s temperature will change in response to rising carbon dioxide (CO2) levels, potentially giving governments more confidence to prepare for the future.
The results suggest that, when it comes to the climate, both the doom-mongers and optimists are wrong. On the other hand, they have prompted a heated debate over how certain you can be about uncertainty.
‘People are quite rightly looking at what we’ve done, because we’re claiming quite a big reduction in uncertainty, based on a pretty simple analysis,’ said lead author Professor Peter Cox of the University of Exeter in the UK.
The climate is a complex beast. To make predictions about how much temperatures will rise in the future, scientists employ hugely detailed computer simulations, which rely on swathes of experimental data as input.
But there is a big unknown in these simulations: how much warming do you get for a certain amount of CO2? This simple parameter is known as the climate’s sensitivity, and it dominates our uncertainty about future global warming.
Normally, climate sensitivity is estimated by looking at historical data on temperature and greenhouse gases – either measurements of global warming or records of past climates, such as ice cores and tree rings. Given a rise in CO2 and a concurrent rise in temperature, scientists can judge how much the former affects the latter.
Big range
For the past 25 years or so, studies based on this method have led the Intergovernmental Panel on Climate Change (IPCC) to conclude that the sensitivity of the Earth to a doubling in CO2 falls in a ‘likely’ range of 1.5°C to 4.5°C, with a central estimate of 3°C.
Prof. Cox believes this degree of uncertainty isn’t good enough. ‘I think it’s slightly embarrassing that we’ve had a range that is so large for so long,’ he said.
‘I think it’s slightly embarrassing that we’ve had a range that is so large for so long.’ – Prof. Peter Cox, University of Exeter, UK
To avoid this problem, Prof. Cox and colleagues ignore the historical warming trend altogether, and instead picture the climate as a spring. The length of the spring is the global temperature, and the weights on the end are the net heating due to CO2 and aerosols.
Crucially, to work out the sensitivity using this new method, Cox and his co-authors don’t actually need to know how much weight there is. All they need to do is measure the spring’s stiffness, and this is betrayed by how quickly the spring oscillates – or in real terms, how much temperatures have varied from year to year.
A ‘stiff’ climate equals a small sensitivity, while a ‘slack’ climate equals a big sensitivity. In their paper published in the journal Nature, Prof. Cox and colleagues estimate the sensitivity to be in the ‘likely’ range of 2.2°C to 3.4°C – less than half the range given by the IPCC.
Sensitive figures
To be clear, this range is not necessarily how much warming anyone should expect. It only reflects how much warming there would be for a doubling of CO2 levels since the baseline period of pre-industrialisation – although we’re about halfway to that threshold already.
Nevertheless, the researchers’ results appear to simultaneously exclude the very worst- and best-case scenarios. ‘I sort of see this as good news, in that our range says values above 4°C are unlikely, and so we’re not yet too late to avoid the 2oC limit set by the Paris Agreement,’ said Prof. Cox.
But not everyone is on board with the new statistics. Climate scientist Professor Tapio Schneider of Caltech in California, US, believes the researchers have mistakenly assumed that their springy relationship is linear, when it could be more complicated.
This view is not shared by Dr James Annan of Blue Skies Research in the UK. On his blog he describes himself as a ‘fan’ of the new approach, albeit ‘not uncritically’.
Professor Reto Knutti of ETH Zürich in Switzerland points out that Prof. Cox and colleagues are not the first to try an alternative method to cut the uncertainty surrounding climate sensitivity, and ‘it’s not obvious why theirs should be much better than others’.
‘So while I do find those emergent constraints promising, and I hope we will be able to narrow the range eventually, there is a danger of finding spurious and not robust correlations – the result being that error bars are too small,’ he added.
Prof. Cox admits that his group’s results will probably not be the last word, but he is hopeful that they can move the science of climate uncertainty forwards, beyond the IPCC range.
‘I think there’s good reason to believe climate scientists are now ready to reduce the long-standing uncertainty in ECS (equilibrium climate sensitivity). It is high-time that we did that,’ he said.
###
The study: https://www.nature.com/articles/nature25450
Emergent constraint on equilibrium climate sensitivity from global temperature variability
Abstract
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.
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“…climate sensitivity is estimated by looking at historical data on temperature and greenhouse gases…” I would assume that during the last glacial period during which a sheet of ice a mile thick covered much of Canada, atmospheric humidity would have been very low. With a significant decrease in atmospheric water vapor content, that major greenhouse gas reduction would definitely have lowered world temperatures – lowered CO2, not so much.
And to summarize . A series of wild ass guesses with a range all over the map .
So this is what “scientific consensus ” looks like ?
Just imagine if they could actually accurately do math models that demonstrated the
cause and effect of natural variables that are still running the show .
Yes, Mark, I agree with you that given what was known in his time Newton’s interest in alchemy was not unscientific. Elements cannot be transformed into each other by chemical means but substances in nature do not come to us labeled “element”, “compound” or “mixture”. Thus water was long thought to be an element but turned out to be a compound and air was long thought to be an element but turned out to be a mixture.
There is a tendency to describe discarded or disproven past scientific theories as “pseudoscience”. Thus the phlogiston theory is often described as “pseudoscientific” although it was supported in it’s time by the eminent chemist Joseph Priestly. Lord Kelvin believed in the ether theory and Maxwell expended great efforts on attempting to develop a mechanical theory of electromagnetism. These theories were eventually discarded but that does not mean that Kelvin or Maxwell were “pseudoscientists”. Just that they were wrong about some things.
The problem, as I am tiring of restating, is that there is no such thing as an “equilibrium climate sensitivity,” because there is no such thing as an equilibrium climate state. Just for starters, the solar energy input to the earth varies by +/- 47 W/m^2 every 182.5 days. That’s an order of magnitude above the supposed retention of energy by CO2. the short term fluctuations due to cloud albedo can change the balance by +/- 4% on an hourly basis, with no ability to predict. Cloud cover isn’t predictable by any current physical model And it isn’t averagable. The whole premise of an equilibrium climate sensitivity is false. There can be no such thing. So it isn’t any wonder that no progress is made on analyses based around it.
R. Clark has one of the best descriptions on Ghg effect…. Including line broadening….search for this
.THE GREENHOUSE EFFECT
Roy Clark PhD
Ventura Photonics
Thousand Oaks, CA
Ventura Photonics Monograph VPM 003.1
January 2018
The error bars in pseudo-temperature are typically bigger than the pseudo-effect. When they are not, they are contradicting each other heavily. This is not science, it’s religion.
It is a religion and the bishops of Climate are still collecting funds from the poor while the monks in their abbeys continue the struggle to determine how many angels can stand on the point of a pin.
Based on my family history over several generations, my expected life span is between 42 and 103 years.
With that level of uncertainty, I’ll never die
What is a “probability”?
“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. ” Extract from the Abstract
My comment
It also equally follows that the possibility of a value of ECS towards the LOWER end of this range (1.5 to say 2 c ) increases the feasibility of even beating or at least meeting the Paris Agreement global temperature target of 2 c increase without taking any action.
I suggest this is just as valid a position to adopt as the one adopted above by Professor Cox as the rationale for making his “spring analogy” ECS analysis ( which one contributor says anyway is not consistent with Hooke’s equation to measure the responsiveness of a spring)