by Judith Curry
Attribution of climate change and its impacts has been a recurring theme at Climate Etc. The first issue of Nature Climate Change has a provocative article entitled “Overstretching Attribution.”
Overstretching Attribution
Camille Parmesan, Carlos Duarte, Elvira Poloczanska, Anthony Richardson, Michael Singer
Abstract. The biological world is responding rapidly to a changing climate, but attempts to attribute individual impacts to rising greenhouse gases are ill-advised.
Nature Climate Change 1, 2-4 (2011) doi:10.1038/
Published online 20 March 2011
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She has also been active in climate change programs for many international conservation organizations, such as IUCN (the International Union for the Conservation of Nature), the WWF (World Wildlife Fund), and the National Wildlife Federation, and served on the Science Council of the Nature Conservancy. She was a Lead Author and Contributing author of the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (2001), as well as a Co-author of the Uncertainty Guidance Report and reviewer for the IPCC Fourth Assessment Report (2007).
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The paper starts with this rather astonishing paragraph (astonishing in the Nature venue):
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Richard Lindzen of the Massachusetts Institute of Technology was once quoted in NewsMax magazine saying: “Climate change is the norm. If you want something to worry about, it would be if the climate were static. It would be like a person being dead.” Lindzen is that rare but conspicuous animal: a bona fide climate scientist who rejects the scientific consensus that current climate warming is largely caused by human emissions of greenhouse gases.
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The Introduction further states:
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As biological impacts provide evidence of climate change independently of temperature measurements, they have successfully bolstered ‘detection’, strengthening the scientific consensus that Earth is warming. However, now that warming is “unequivocal”, contrarian arguments have shifted from whether warming is happening to whether it can be attributed to human activity. In this context, biologists are now expected to shift away from detection towards attribution — that is, assessing the extent to which observed biological changes are being driven by greenhouse-gas-induced climate change versus natural climate variability. This expectation is formalized in a guidance paper for scientists taking part in the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC)1.
In theory, this is a scientifically sound approach. In practice, we argue that these expectations are misguided when applied to most biological data. It is rarely possible to attribute specific responses of individual wild species to human-induced climate change. This is partly because human forcing of the climate is only detectable on large spatial scales, yet organisms experience local climate. Moreover, in any given region, species’ responses to climate change are idiosyncratic, owing to basic differences in their biology. A further complication is that responses to climate are inextricably intertwined with reactions to other human modifications of the environment. Even where climate is a clear driver of change, little insight is gained by asking what proportion of the overall trend is due to greenhouse gases versus solar activity. From the perspective of a wild plant or animal, a changing climate is a changing climate, irrespective of its cause.
The section on biological complexities states:
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The IPCC guidance paper states that attribution seeks to determine whether a specified set of drivers are the cause of an observed change in a specific system1. However, the probability of successfully attributing climatic trends to greenhouse gases declines sharply at spatial scales smaller than 106 km2 and at temporal scales shorter than 50 years. Therefore, studies linking biological changes to anthropogenic climate change are likewise most robust at continental to global scales. A corollary of this limitation is that it is inappropriate to attribute single events to anthropogenic climate change.
Another challenge for biological attribution is that global average trends in impacts camouflage a striking diversity of responses, even among species living in the same area and subject to the same climatic changes.
Some of this diversity stems from basic differences in species’ sensitivity to climate. However, there is also a complex interplay among habitat destruction, land-use change, exploitation and pollution, in addition to climate change. The emerging view is that interactions among drivers of change are the norm.
From the section on anthropogenic attribution:
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The IPCC1 believes that it is, and advocates an ever-more-detailed approach to attribution. We disagree. We argue that ‘chained-attribution’ assessments from greenhouse gases to climate change to biological change, as called for by the IPCC, are largely inappropriate, principally because our understanding of the biological impacts of climate change cannot aspire to the level achieved in physical climate science. This is not simply a matter of further research, for there is no common biological response to a single climate driver, and no simple biological metric analogous to global temperature rise. Each ecosystem, species, or even population can respond differently to climate change, and there are an estimated 30–100 million species. Thus, we are far from being able to achieve realistic coupled climate–biological models, and in an attempt to reach this goal, we risk taking research effort away from the critical issue of adaptation.
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From the concluding section entitled A way forward:
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What, then, are the most productive avenues for biological attribution research? We propose concentrating on assessment of the interacting roles of climate and other environmental factors, regardless of the causes of the climate events or trends. Such ‘attribution’ assessment would involve synthesizing multiple lines of evidence linking climate drivers with species’ responses, such as empirical studies on physiological thresholds and preferences for thermal environment, precipitation or ocean pH. It would also include palaeontological evidence for correlations between species’ changes and climate drivers in the past, and tools such as species niche models that can link observed changes in distributions to particular environmental drivers. Although this approach has been advocated in earlier IPCC reports, the importance of multi-faceted empirical assessment has been recently de-emphasized in favour of model-based approaches.
By over-emphasizing the need for rigorous assessment of the specific role of greenhouse-gas forcing in driving observed biological changes, the IPCC effectively yields to the contrarians’ inexhaustible demands for more ‘proof’, rather than advancing the most pressing and practical scientific questions. This focus diverts energies and research funds away from developing crucial adaptation and conservation measures.
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JC’s comments: More of this please! I wish someone would write an analogous article on the attribution of extreme weather events. It seems that the same kind of arguments could be made for attribution of human stresses. The broader implications of this paper is that it has seriously undercut the rationale for the entire IPCC WG II Report.
