by Judith Curry
Estimates of climate-change impacts will get less, rather than more, certain. But this should not excuse inaction, say Mark Maslin and Patrick Austin.
A recent article was published in Nature, titled Climate Models at Their Limit? by Mark Maslin and Patrick Austin. The paper is of course behind paywall, here are some excerpts:
For the fifth major assessment of climate science by the Intergovernmental Panel on Climate Change (IPCC), due to be released next year, climate scientists face a serious public-image problem. The climate models they are now working with, which make use of significant improvements in our understanding of complex climate processes, are likely to produce wider rather than smaller ranges of uncertainty in their predictions. To the public and to policy- makers, this will look as though the scientific understanding of climate change is becom- ing less, rather than more, clear.
Scientists need to decide how to explain this effect. Above all, the public and policy- makers need to be made to understand that climate models may have reached their limit. They must stop waiting for further certainty or persuasion, and simply act.
The climate models, or ‘climate simulators’ as some groups are now referring to them, being used in the IPCC’s fifth assess- ment make fewer assumptions than those from the last assessment, and can quantify the uncertainty of the complex factors they include more accurately. Many of them contain interactive carbon cycles, better representations of aerosols and atmospheric chemistry and a small improvement in spatial resolution.
Yet embracing more-complex processes means adding in ‘known unknowns’, such as the rate at which ice falls through clouds, or the rate at which different types of land cover and the oceans absorb carbon diox- ide. Preliminary analyses show that the new models produce a larger spread for the pre- dicted average rise in global temperature. Additional uncertainty may come to light as these models continue to be put through their paces. Dan Rowlands of the University of Oxford, UK, and his colleagues have run one complex model through thousands of simulations, rather than the handful of runs that can usually be managed with available computing time. Although their average results matched well with IPCC projections, more extreme results, including warming of up to 4 °C by 2050, seemed just as likely. As computing power becomes more accessible, that ‘hidden’ uncertainty will become even more obvious.
The biggest obstacle is the unwillingness of politicians to act in the long-term interests of society. Politicians use public opin- ion and scientific uncertainty as excuses for inaction. They used to say “we need to wait until scientists prove that mankind is caus- ing climate change”. That hurdle has, argu- ably, passed, so now they have moved on to “we need to wait until scientists can tell us exactly what will happen and what the costs are”, or, “we need to wait for public opinion to be behind action”. The former will never occur, because modelling can never provide that level of certainty. The latter is a sleight of hand. Politicians often take action without public support, from wars to bank bailouts, taxation to health-care reforms.
Greater knowledge and improved models will always be desirable, but they are not a panacea for political and public reticence to action on climate change. Despite the uncertainty, the weight of scientific evidence is enough to tell us what we need to know. We need governments to go ahead and act, as both the United Kingdom and Mexico have done in making national laws that contain carbon reduction targets of 80% and 50%, respectively, by 2050. We do not need to demand impossible levels of cer- tainty from models to work towards a better, safer future.
JC comments: I didn’t post on this when it first came out, since Tamsin Edwards did a nice post on it [link; the comments are very good also]. The paper provides a realistic assessment of model capabilities and uncertainties, and the dilemma of growing uncertainties as the models improve and become more complex. The main point I want to make is in context of my previous post No consensus on consensus.
The ‘speaking consensus to power’ approach can be characterized to a substantial extent as ‘speaking climate model simulations to power.’ In this context, increasing uncertainty in the climate models simulations is bad news for the politics of CO2 mitigation. I’ve argued in the previous post that that the ‘scientific truth to power’ model just doesn’t make sense for the wicked climate problem. Using climate models in ‘speaking climate model simulations to power’ isn’t a good use of climate models, given their limitations.
The new climate model simulations for AR5 are substantially improved, with a much better experimental design. We stand to learn much from this collection of model simulations. But we need to ask the question of how climate models can best support decision making for a broad range of possible future scenarios and decision making objectives. My next paper will address this issue, here is the tentative title: Climate Models: Fit For What Purpose? The paper will take on my presentation to DOE BERAC.
tamsin’s blog, jvs email