Collectively, the current IPCC computer modelled scenarios for the iconic doubling of atmospheric CO2 range from 1.1C to 6.4C, with a ‘most likely’ range of 2C to 4.5C. Higher estimates have a much lower probability of being accurate.
In this week’s Science magazine there are two related papers that discuss climate sensitivity:
Why Is Climate Sensitivity So Unpredictable?
Gerard H. Roe* and Marcia B. Baker
Uncertainties in projections of future climate change have not lessened substantially in past decades. Both models and observations yield broad probability distributions for long-term increases in global mean temperature expected from the doubling of atmospheric carbon dioxide, with small but finite probabilities of very large increases. We show that the shape of these probability distributions is an inevitable and general consequence of the nature of the climate system, and we derive a simple analytic form for the shape that fits recent published distributions very well. We show that the breadth of the distribution and, in particular, the probability of large temperature increases are relatively insensitive to decreases in uncertainties associated with the underlying climate processes.
Myles R. Allen and David J. Frame
Over the past 30 years, the climate research community has made valiant efforts to answer the “climate sensitivity” question: What is the long-term equilibrium warming response to a doubling of atmospheric carbon dioxide? Earlier this year, the Intergovernmental Panel on Climate Change (1) concluded that this sensitivity is likely to be in the range of 2° to 4.5°C, with a 1-in-3 chance that it is outside that range. The lower bound of 2°C is slightly higher than the 1.6°C proposed in the 1970s (2); progress on the upper bound has been minimal.
In a nut shell, the limits have been reached for model estimations of the upper bound and therefore even more complex models will be unable to resolve the greater uncertainty of higher bound estimates, so it’s time to “call off the search.”
New Scientist’s take is:
Climate is too complex for accurate predictions
Excerpt: “This finding reinforces not only that climate policies will necessarily be made in the face of deep, irreducible uncertainties,” says Roger Pielke, a climate policy expert at the University of Colorado at Boulder, US. “But also the uncomfortable reality – for climate modellers – that finite research dollars invested in ever more sophisticated climate models offer very little marginal benefit to decision makers.”
Personally, I disagree with the statement made in Science magazine that “This persistent, high-temperature tail of low probability has been one impediment to political action, as policy-makers have been reluctant to formulate policies to address climate change when the range of uncertainty is so large.” If this is true, then I haven’t noticed.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Oh well – perhaps we should see what happened in the past … hmmm 2.9C or ask a solar guy on stats not modelling – 2.9C….. fizzle….
Given that climate models rely heavily on secondary data sources it is not surprising that it is difficult to determine the levels of uncertainty surroundng climate mdel projections. Unfortunately where data is collected for reasons other than climate modelling it will always be difficult to determine the accuracy or precision of the model outputs.
Luke,
Obviously your lotto numbers?
And only the scientifically illiterate would confuse degrees Celsius with Kelvins.
As we are about 75% of the way to a doubling of atmosphere CO2 from an assumed baseline of 280 ppmv, and the measured temperature increase that most agree on is about 0.6 degrees Celsius for the same period, then this fact tends to support Richard Lindzen’s statement that climate sensitivity is about 1 degree Celsius from first principles.
The computer models are therefore somewhat incomplete.
What do the climate models say will happen for 75% of a doubling of CO2? Or in other words what do the climate models claim is the state of climate right this moment?
You know and I know that the climate modelers won’t dare make a prediction of the weather for next year – because their climate models would be proven conclusively useless.
But hang on Louis – you’ve repeated over and over again that there is no CO2 greenhouse effect? Have you suddenly changed your mind.
Well we know by now both of us have problems with basic maths (sign of genius I’m told 🙂 )
Isn’t 2 X CO2 560 ppm. Isn’t a 36% increase in 280ppm about 381ppm – about where we are now.
75?% ???
No Louis not Lotto – actually were from what we call science. But you’d have to have reading skills which we know you lack. But funny – one’s geological and one’s solar. How ironic. ROTFL.
http://www.amath.washington.edu/research/articles/Tung/journals/solar-jgr.pdf
http://droyer.web.wesleyan.edu/climate_sensitivity.pdf
Climate isn’t weather James.
For a start, the 0.6C increase over the past century is more and more tenuous every day. The increase in CO2 from 280ppm to 380ppm has made no change to North American temperatures since the 1930’s. And even allowing for the rapid dispersal of North American CO2, (which we are told has been the major source of global emissions over the past century) there is still no residual warming at the source.
And given the unreliability of Soviet, Chinese, Indian, Middle Eastern, African and Latin American data over this period, there are ample grounds for concluding that the 0.6C warming figure has been plucked out of someones backside.
Add to that the complete under-representation of oceanic temperatures in the global mean, and the fact that southern hemisphere temperatures have shown much less rise at the same CO2 levels, and this 0.6C assumption from a 100ppm rise in CO2 is looking very sad indeed.
And for what? The daily temperature variation between Brisbane CBD and Ipswich is normally 2.0C over a distance of only 25km as the cliches fly. So we are working ourselves into a lather about the consequences of a 7.5km drive down the western distributor.
That should really scare the punters in Kenmore.
Could anyone advise us what the actual numbers are? We are told that there is a 0.33 probability of the sensitivity being outside the range of 2.0 to 4.5C but it is unclear how this 0.33 is distributed above and below.
The southern hemisphere series is shown here; http://cdiac.ornl.gov/ftp/trends/temp/jonescru/sh.dat
The only problem is that is based on Jones (need I say more). But even so, it makes it clear that most of the warming took place prior to 1938. That is, before CO2 levels hit 300ppm.
And it is clear that the analysis that indicates a 2.0 to 4.5C sensitivity is heavily reliant on extrapolation from this early, unreliable data.
Ah crap Ian – here we go – inability to separate out the solar and greenhouse drivers. Have we have a big burst of solar activity in the last 30 years? Jeeeezzz…
Are you that thick that you’re going to run a Ipswich to Brisbane daily temperature difference argument. If you don’t why this is a ruse I’m happy to leave you ignorant as paddies. What a bloody stupid argument.
“No residual warming at source” – you actually wrote that. Are you mental? What a wanker.
The data from most European stations show a higher CO2 reading close to cities (ie. the source of the emissions).
And we know that most of the serious increase in temperature comes from a. urban sites and b. Europe. But why?
drat he wouldn’t engage. I hate that.
OK wanna play science then – what about the Antarctic Peninsula, Tasman Sea and mid troposhere above Antarctica. All high levels of warming.