This essay addresses Trenberth's statement that ‘Given that global warming is “unequivocal”, and is “very likely” due to human activities to quote the 2007 IPCC report, the null hypothesis should now be reversed, thereby placing the burden of proof on showing that there is no human influence.’ We examine how the concept of a null hypothesis is being used implicitly and explicitly in the scientific and policy debate on climate change, in the context of scientific hypothesis testing, as a framework for ‘burden of proof’ arguments and policy deliberations, and metaphorically in the context of a polemic. It is argued that the statement of a null hypothesis is not particularly useful in the broader context of the scientific inferences surrounding the topic of the attribution of climate change and also policy decisions. WIREs Clim Change 2011, 2:919–924. doi: 10.1002/wcc.141
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