Climate Hawkins

Ed Hawkins, a climatologist at Reading University, has written a short blog post reporting a comparison he has done of climate model output to data. He specifically addressing the question of the Arctic temperatures, which I mentioned in yesterday's post, masking the model output so as to exclude the Arctic and thus giving an apples-to-apples basis for the comparison.

The models used are the CMIP5 ensemble, which I think I'm right in saying is very recent - within the last year or two. I would be interested in seeing some AR4-era model runs and checking how these panned out against the same temperature data.

Uncertain uncertainty

Richard Rood's article about uncertainty in climate projections is a few weeks old now, but I came across it only today after someone tweeted a link to it. Rood is trying to make the case that:

the uncertainty in climate projections associated with the physical climate model is smaller than the uncertainty associated with the models of emission scenarios that are used to project carbon dioxide emissions.

His argument seems to rest partly on the fact that climate models include well-understood physical laws at their heart, while economic models are much more empirical. This argument seems to me to be somewhat spurious. The fact that an aeroplane includes a number of transistors, whose behaviour is well-understood, does not make it necessarily more likely to fly than one that doesn't.

He argues that the spread in the models would be much less if it were not for the different economic scenarios that feed them. This seems flawed to me. Rood argues that the spread in the models represents "simple estimate of uncertainty". I'm not sure this is right. To the extent that the models make the same erroneous assumptions and have the same unknown unknowns, surely the climate model uncertainty is much larger?

New solar paper

A new paper by Gareth Jones, Mike Lockwood and Peter Stott says that future reductions in solar output will have a limited impact on global warming projections, based on the output from their climate model.

During the 20th century, solar activity increased in magnitude to a so-called grand maximum. It is probable that this high level of solar activity is at or near its end. It is of great interest whether any future reduction in solar activity could have a significant impact on climate that could partially offset the projected anthropogenic warming. Observations and reconstructions of solar activity over the last 9000 years are used as a constraint on possible future variations to produce probability distributions of total solar irradiance over the next 100 years. Using this information, with a simple climate model, we present results of the potential implications for future projections of climate on decadal to multidecadal timescales. Using one of the most recent reconstructions of historic total solar irradiance, the likely reduction in the warming by 2100 is found to be between 0.06 and 0.1 K, a very small fraction of the projected anthropogenic warming. However, if past total solar irradiance variations are larger and climate models substantially underestimate the response to solar variations, then there is a potential for a reduction in solar activity to mitigate a small proportion of the future warming, a scenario we cannot totally rule out. While the Sun is not expected to provide substantial delays in the time to reach critical temperature thresholds, any small delays it might provide are likely to be greater for lower anthropogenic emissions scenarios than for higher-emissions scenarios.

I hope they have made suitable caveats about the validation (or lack of it) of their computer model's ability to project future global warming.

Nordhaus and the sixteen

Economist William Nordhaus takes a pop at the sixteen concerned scientists, in the latest skirmish kicked off by their Wall Street Journal editorial.

My response is primarily designed to correct their misleading description of my own research; but it also is directed more broadly at their attempt to discredit scientists and scientific research on climate change.¹ I have identified six key issues that are raised in the article, and I provide commentary about their substance and accuracy. They are:

• Is the planet in fact warming?
• Are human influences an important contributor to warming?
• Is carbon dioxide a pollutant?
• Are we seeing a regime of fear for skeptical climate scientists?
• Are the views of mainstream climate scientists driven primarily by the desire for financial gain?
• Is it true that more carbon dioxide and additional warming will be beneficial?

Chivers on cosmoclimatology

Tom Chivers says he enjoyed his foray into climate a couple of days ago and has returned to the subject with a piece about Svensmark's cosmoclimatology theory.

...it's an interesting piece of research which adds to our understanding of atmospheric behaviour. As always, it's been leapt upon by "sceptics" who think all climate scientists are charlatans until those scientists say something they agree with, whereupon they're modern-day Galileos being placed under house arrest for heresy by the Church of AGW.

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Nobel laureate on temperatures

Revkin posts what I have to say is an astonishingly fatuous letter from Nobel laureate Burton Richter in response to the letter of the 16 in the Wall Street Journal.

Armed with my own Nobel Medal, I say if you can read a graph, the evidence is indeed incontrovertible because the temperature has gone up. The Physical Society is right, he is wrong, and I can’t understand why he complains about the temperature rise issue when there is more to discuss on the second question; who is the villain?

This is what is known in the trade as a straw man. Nobody is arguing that temperatures have not gone up, including the 16 signatories of the Wall Street Journal letter. Somehow one expects that Nobel laureates would be able to string together a logical argument (or at least that the winners of scientific Nobels would be able to do so).

The 16 scientists note only that temperature hasn't risen for over ten years. This is inconsistent with a world warming at 2 degrees per century and is surprising in view of the increases in greenhouse gases we have seen over the same period.

Let me say it again: the question is not whether temperatures have risen or whether mankind has affected the climate. Temperatures have always risen and fallen and mankind has always affected the climate. The question is whether we have a problem on our hands. The poor performance of the climate models suggests that the problem is much less than we have been led to believe.

Protomodels

To the layman, the word "model" implies a scaled down version of something, correct in all its salient details. We all know the kind of thing.

A climate model is not like that. As everyone knows, climate models are not validated out of sample and we don't know if any of their salient details are correct. Some features of the real world are reproduced on a "hindcast" basis, but the ability of models to make meaningful predictions is more in the realms of hope than established fact.

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Warm weather - Josh 142

George Monbiot's hilarious article 'Do the weather forecasters used by the Daily Mail actually exist?' is well worth reading. Although we know that weather is not climate (except when it is) one can't help but see some parallels.

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Green Alliance on AGW and Russell

Updated on Jan 24, 2012 by Bishop Hill

Alice Bell has written a trailer for Brian Hoskins' lecture at Imperial last Monday - if everything goes technically to plan this should be available as a podcast shortly. The trailer includes Hoskins' recommendations for climate reading - at a newbie level.

Among the documents recommended by Hoskins is the Green Alliance's introduction to climatology, published last year. This was prepared by their own Rebecca Willis, with input from Hoskins and Simon Buckle of the Grantham Institute (the sciencey bit at Imperial, as opposed to the naked-green-activism bit at LSE), and Joanna Haigh of Imperial.

Click to read more ...

Shaviv on models and sensitivity

Richard Betts joined in the conversation about climate models today, making some interesting comments on validation:

As I've mentioned before, the earlier climate models used in the 1970s were used to make estimates of warming over the next 30 years which were fairly close to what happened ... BH asks for tests of the projections made 10 years ago, but the problem is that with internal variability in the system you need longer than that to test the models, unless you specifically initialise the models with the conditions of (say) 2001 using data assimilation techniques, and that kind of thing was not available then, we only started doing it 5 years ago.

So yes, out of sample testing on timescales relevant to GHG rise is an important point but by definition difficult with the latest models!

One minor point is that I had said I would have been more convinced had the story of model versus data in the last ten years been different - I agree with the 30 years figure for falsification. However, more interesting is a point made in a recent post by Nir Shaviv:

From the first IPCC report until the previous IPCC report, climate predictions for future temperature increase where based on a climate sensitivity of 1.5 to 4.5°C per CO₂ doubling. This range, in fact, goes back to the 1979 Charney report published by the National Academy of Sciences. That is, after 33 years of climate research and many billions of dollars of research, the possible range of climate sensitivities is virtually the same! In the last (AR4) IPCC report the range was actually slightly narrowed down to 2 to 4.5°C increase per CO2 doubling (without any good reason if you ask me). In any case, this increase of the lower limit will only aggravate the point I make below, which is as follows.

Because the possible range of sensitivities has been virtually the same, it means that the predictions made in the first IPCC report in 1990 should still be valid. That is, according to the writers of all the IPCC reports, the temperature today should be within the range of predictions made 22 years ago. But they are not!

Go and take a look at the graph at Nir's site. This seems a reasonable point to me.

Mann, straw man and SciAm

Michael Mann is in Scientific American today, with a podcast discussing computer models and the hockey stick man has a pop at Freeman Dyson:

I have to wonder if Freeman Dyson will get on an airplane or if he’ll drive a car because a lot of the modern day conveniences of life and a lot of our technological innovations of modern life are based on phenomena so complicated that we need to be able to construct models of them before we deploy that technology.

 This is a bit of straw man, and Mann in fact goes on to discuss the fact that

we can’t do experiments with multiple Earths and formulate the science of climate change as if it’s an entirely observationally based, controlled experiment.

However, after a lot of words about how models are used, he returns to his strawman.

And again, does Freeman Dyson, assuming he is willing to get on an airplane even though models have been used to test the performance of the airplane, assuming he does and he knows he’s going somewhere where they’ve predicted, where weather models have predicted rainfall for the next seven days, does he not pack his umbrella because he doesn’t believe the models? It's just in that case the worst that will happen is somebody gets wet when they wouldn’t otherwise have. In this case, the worst that can happen is that we ruin the planet.

It's not desperately edifying, is it?

It's better than we thought

A new paper by Gillett et al finds that transient climate response (i.e. short-term sensitivity) is lower than previously thought.

Projections of 21st century warming may be derived by using regression-based methods to scale a model's projected warming up or down according to whether it under- or over-predicts the response to anthropogenic forcings over the historical period. Here we apply such a method using near surface air temperature observations over the 1851–2010 period, historical simulations of the response to changing greenhouse gases, aerosols and natural forcings, and simulations of future climate change under the Representative Concentration Pathways from the second generation Canadian Earth System Model (CanESM2). Consistent with previous studies, we detect the influence of greenhouse gases, aerosols and natural forcings in the observed temperature record. Our estimate of greenhouse-gas-attributable warming is lower than that derived using only 1900–1999 observations. Our analysis also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively low projections of 21st-century warming under the Representative Concentration Pathways. Repeating our attribution analysis with a second model (CNRM-CM5) gives consistent results, albeit with somewhat larger uncertainties.

It's still a model though, isn't it?

Hulme on climate modellers

Via Hans von Storch (who calls it `remarkable') comes this paper from Mike Hulme on how climate modellers have imposed a hegemony on academic thought about the climate.

One hundred years ago, a popular theory contended that various aspects of climate determined the physiology and psychology of individuals, which in turn defined the behavior and culture of the societies that those individuals formed. As the ideological wars of the twentieth century re-shaped political and moral worlds, environmental determinism became discredited and marginalised within mainstream academic thought. Yet at the beginning of a new century with heightening anxieties about changes in climate, the idea that climate can determine the fate of people and society has re-emerged in the form of ‘climate reductionism’. This paper traces how climate has moved from playing a deterministic to a reductionist role in discourses about environment, society and the future. Climate determinism previously offered an explanation, and hence a justification, for the superiority of certain imperial races and cultures. The argument put forward here is that the new climate reductionism is driven by the hegemony exercised by the predictive natural sciences over contingent, imaginative and humanistic accounts of social life and visions of the future. It is a hegemony which lends disproportionate power in political and social discourse to model-based descriptions of putative future climates. Some possible reasons for this climate reductionism, as well as some of the limitations and dangers of this position for human relationships with the future, are suggested.

(The link in the paper is to a preprint - I hope somebody picked up the misspelling of Geoffrey/Jeffrey Sachs name in the meantime. Although perhaps I don't - it's always good to have people in Sachs position brought crashing down to Earth occasionally.)

The Ecologist talks sense

No, really. I found a really quite sensible article in the Ecologist about global warming and in particular about climate models.

Mistakes, cover-ups and inaccuracies have served to undermine many people’s faith in climate science at a time when its work is more important than ever.

A bunch of aerosols - Josh 125

Click for a slightly larger image