A panel debate

I was in St Andrews yesterday, appearing at a discussion/debate for third year students in the Earth Sciences department. We were discussing the usefulness of climate models as policy tools (a subject I had suggested, as it involved the least work for me!) The event was hosted by Dr Tim Hill and putting a more mainstream view was Rob Wilson, although I think our views were probably too close to really create any fireworks. Rob's nuanced views on the climate debate also seemed to have rubbed off on his students, as although there was some close questioning at the end there was none of the outright hostility that one sometimes gets on these occasions.

Thanks to Rob and Tim for lunch and an interesting afternoon.

New climate consensus: GCMs are lousy

The models are lousy and probably wrong. In which direction they are wrong is not clear at all, yet.

Eduardo Zorita's comments on climate models are interesting. Given the strong evidence that the models run too warm, I think he is being far too even handed, but perhaps more interesting is the way his words echo the terminology used by the UK's top climate modeller Brian Hoskins.

Interviewer: Tell us the war story. How bad were the climate models when you started out?

Brian Hoskins: Ah, they were pretty lousy, and they're still pretty lousy, really. They were terrible.

I think we could say that there is a consensus here, but rest assured that it a bad case of climate denial to suggest that GCMs are not suitable tools for policymakers.

Update on Nov 10, 2014 by Bishop Hill

Interesting to compare these comments to Keith Shine's description of the climate models to parliamentarians.

...state-of-the-art climate models, which are our embodiment of the laws of physics as applied to the atmosphere...

I was roundly criticised by some for suggesting that Shine's words were misleading.

Stratospheric persistence

Climatologists are nothing if not persistent. A new paper by a large team of climate scientists, among them Susan Solomon and Ben Santer, reckons it has found the reason for the model-observations divergence. I think this brings the tally of explanations to over 40 now. The correct answer, it seems, is that aerosol cooling, in particular that due to volcanoes, has been severely underestimated:

Understanding the cooling effect of recent volcanoes is of particular interest in the context of the post-2000 slowing of the rate of global warming. Satellite observations of aerosol optical depth (AOD) above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, AERONET and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at mid to high latitudes, and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be −0.19 ± 0.09 Wm⁻². This translates into an estimated global cooling of 0.05 to 0.12 °C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.

I'm not sure what they've actually done, since the paper is paywalled. No doubt the credibility of their claims will be examined over the next couple of days.

McLean on clouds

John McLean, of James Cook University in Australia, emails with details of a paper he has just had published in Atmospheric and Climate Sciences about the warming of the planet at the end of the last century. He adds a useful layman's summary.

The paper ...

- indicates that the temperature pattern can be attributed to a sequence of events, namely a shift in the prevailing ENSO conditions, then a reduction in total cloud cover and then a shift on cloud (decrease in low level cloud that was largely offset by an increase in mid and upper level cloud)

- uses the Trenberth, Fasulo & Kiehl energy balance diagram to show that the loss in total cloud cover caused an increase in heat energy being absorbed at the Earth's surface that was greater than the increase that IPCC 5AR claims was due to greenhouse gases

Click to read more ...

Climate models and rainfall

I have a new briefing paper out at GWPF looking at the question of rainfall, flood and global warming. Here's the press release:

London, 10 October: A new briefing paper from the Global Warming Policy Foundation reviews the scientific literature on rainfall and floods and finds little evidence that there have been significant changes in recent years and little support for claims that they will become worse in future.

Despite claims to the contrary, there has been no significant change in rainfall trends in recent years both at global and UK levels. It remains very difficult to make strong claims about any changes there have been because of high natural variability in rainfall patterns, particularly in the UK.

Rainfall is a particularly difficult area for climate models, which have limited ability to recreate what is seen in the real world. Since these climate models are the main basis of claims that extreme rainfall and flooding events are being adversely affected by man-made global warming and that rainfall will become worse in the future, policymakers should treat such modelling with extreme caution.

Author Andrew Montford said, “We are constantly bombarded with insinuations that storms and floods are caused by or ‘linked to’ climate change.”

“In reality these claims are usually based on climate models, which have a demonstrable inability to tell us anything reliable about rainfall. The scientific evidence shows that a simple extrapolation of rainfall averages over time can give better rainfall predictions than climate models,” he added.

Here's the paper.

Climate models and clouds

Idly looking for something to write about this morning I sidled over to Geophysical Research Letters where my eye alighted on the abstract of a paper by Cheruy et al. It concerns the CMIP5 climate models and considers clouds and the transfer of moisture from land to atmosphere. Here's the abstract:

Over land, most state-of-the-art climate models contributing to Coupled Model Intercomparison Project Phase 5 (CMIP5) share a strong summertime warm bias in midlatitude areas, especially in regions where the coupling between soil moisture and atmosphere is effective. The most biased models overestimate solar incoming radiation, because of cloud deficit and have difficulty to sustain evaporation. These deficiencies are also involved in the spread of the summer temperature projections among models in the midlatitude; the models which simulate a higher-than-average warming overestimate the present climate net shortwave radiation which increases more-than-average in the future, in link with a decrease of cloudiness. They also show a higher-than-average reduction of evaporative fraction in areas with soil moisture-limited evaporation regimes. Over these areas, the most biased models in the present climate simulate a larger warming in response to climate change which is likely to be overestimated.

If I'm understanding this correctly, when you consider climate models' simulation of clouds and land-atmosphere coupling, the warmer models show the most marked biases against observations.

But don't worry, they are just fine and dandy for informing policymakers.

More Curry

Another day, another Judith Curry paper. This time it's in Geophysical Research Letters and is concerns the much-neglected question of just how good climate models are at hindcasting:

The bulk of our knowledge about causes of 20^th century climate change comes from simulations using numerical models. In particular, these models seemingly reproduce the observed nonuniform global warming, with periods of faster warming in 1910–1940 and 1970–2000, and a pause in between. However, closer inspection reveals some differences between the observations and model simulations. Here we show that observed multidecadal variations of surface climate exhibited a coherent global-scale signal characterized by a pair of patterns, one of which evolved in sync with multidecadal swings of the global temperature, and the other in quadrature with them. In contrast, model simulations are dominated by the stationary — single pattern — forced signal somewhat reminiscent of the observed “in-sync” pattern most pronounced in the Pacific. While simulating well the amplitude of the largest-scale — Pacific and hemispheric — multidecadal variability in surface temperature, the model underestimates variability in the North Atlantic and atmospheric indices.

The inescapable urge to indoctrinate

The latest edition of School Science Review, a journal of the Association for Science Education, is a climate change special, featuring a review of mainstream positions on global warming by Eric Wolff and a host of other articles covering everything from how better to get children on board the global warming bandwagon to a look at biofuels.

Most of it is paywalled, but you can see the covering editorial here, although to tell the truth it's not particularly exciting. I was struck only by this sentence:

Some teachers may not agree that it is our duty to campaign but we surely have a duty to inform our students where the science is clear, and it is important to teach them about what is complex and uncertain and not known.

Click to read more ...

A marvel and a mystery

Updated on Sep 11, 2014 by Bishop Hill

A warm welcome to the climate blogosphere for Kate Marvel, a theoretical-turned-climate physicist at the Lawrence Livermore laboratory.

Dr Marvel's new blog can be seen here, and the first couple of posts make fascinating reading. Today's effort is right up my street, considering the empirical evidence for global warming.

[I]ncreased carbon dioxide warms the lower atmosphere (closer to Earth), but cools the upper atmosphere (closer to space).  I will probably write more about this later but for right now you'll have to take my word for it (or go here).

Click to read more ...

What every politician should know about climate models

Last week Richard Betts of the Met Office got a bit grumpy with me over my comments about Keith Shine FRS. In discussing remarks Shine had made to parliamentarians about climate models I had said that I felt it was grossly misleading of him to restrict his remarks about their reliability to a reference to "...state-of-the-art climate models, which are our embodiment of the laws of physics as applied to the atmosphere..." Richard felt this was unfair, noting Shine's high integrity.

Shine has certainly never come to my attention before as one of the "bad guys" so I am happy to accept Richard's assurances on this point. Nevertheless, I stand by my comments. What Shine told his audience about GCMs gave a thoroughly misleading impression of how reliable GCMs are. This is perhaps understandable as Shine speaking as part of a panel of prominent scientific peers, all of whom were keen to get the message across to the parliamentarians, all of whom were keen to hear a message of alarm (this was the All Party Parliamentary Climate Change Group, after all). In such an atmosphere it's easy to overstep the mark.

Click to read more ...

Quote of the day, ditch the scientific method edition

You’re allowed to say, well I think we should do nothing. That’s a policy choice. But what you’re not allowed to do is to claim there’s a better estimate of the way that the climate will change, other than the one that comes out of the computer models. It’s nonsensical to say ‘we know better’, you can’t know better.

Professor Brian Cox appears averse to the idea that data trumps hypothesis.

Hiding the pause

Corrine le Quere of UEA is another of the scientists who were asked to address the All-party Climate Change Group about AR5, her topic being what is the evidence for that man is causing climate change. Audio is here, her slides can be seen here, an example of which is shown below:

Click to read more ...

GCMs and public policy

In the thread beneath the posting about the Chen and Tung paper, Richard Betts left a comment that I thought was interesting and worthy of further thought.

Bish, as always I am slightly bemused over why you think GCMs are so central to climate policy.

Everyone* agrees that the greenhouse effect is real, and that CO2 is a greenhouse gas.
Everyone* agrees that CO2 rise is anthropogenic
Everyone** agrees that we can't predict the long-term response of the climate to ongoing CO2 rise with great accuracy. It could be large, it could be small. We don't know. The old-style energy balance models got us this far. We can't be certain of large changes in future, but can't rule them out either.

Click to read more ...

Diary dates: physics edition

Joanna Haigh is going to be speaking on the physics of climate change tonight as part of the Royal Society's summer science season.

Earth’s climate is the result of interactions between multiple physical systems, such as the circulation of the oceans, winds and weather patterns, the amount of carbon dioxide in the atmosphere, or the amount of sunlight we receive. In order to understand how the climate is behaving, and how it might behave in the future, we have to understand the fundamental laws controlling these interactions: we have to understand the physics.  Join Joanna Haigh as she explains the integral role of physics in climate science and how its use has transformed our ability to model and predict climate change.

Details: 6:30 pm — 7:30 pm on Friday 04 July 2014 at The Royal Society. No ticket required

What the public needs to know about GCMs

Anthony has a completely brilliant comment from Robert Brown about the ensemble of climate models and the truth about them that is never explained to the public:

...until the people doing “statistics” on the output of the GCMs come to their senses and stop treating each GCM as if it is an independent and identically distributed sample drawn from a distribution of perfectly written GCM codes plus unknown but unbiased internal errors — which is precisely what AR5 does, as is explicitly acknowledged in section 9.2 in precisely two paragraphs hidden neatly in the middle that more or less add up to “all of the `confidence’ given the estimates listed at the beginning of chapter 9 is basically human opinion bullshit, not something that can be backed up by any sort of axiomatically correct statistical analysis” — the public will be safely protected from any “dangerous” knowledge of the ongoing failure of the GCMs to actually predict or hindcast anything at all particularly accurately outside of the reference interval.