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WIREs Clim Change
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Attribution of climate variations and trends to human influences and natural variability

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Past attribution studies of climate change have assumed a null hypothesis of no role of human activities. The challenge, then, is to prove that there is an anthropogenic component. I argue that because global warming is “unequivocal” and ‘very likely’ caused by human activities, the reverse should now be the case. The task, then, could be to prove there is no anthropogenic component to a particular observed change in climate, although a more useful task is to determine what it is. In Bayesian statistics, this change might be thought of as adding a ‘prior’. The benefit of doubt and uncertainties about observations and models are then switched. Moreover, the science community is much too conservative on this issue and too many authors make what are called ‘Type II errors’ whereby they erroneously accept the null hypothesis. Global warming is contributing to a changing incidence of extreme weather because the environment in which all storms form has changed from human activities. WIREs Clim Change 2011, 2:925–930. doi: 10.1002/wcc.142

Figure 1.

A small change in the average temperature value can have a large effect on extremes. Top: The probability of different temperature readings when the mean temperature is 10°C and SD 5.6°C (black curve, A), and when the mean temperature rises 2.8°, to 12.8°C (blue curve, B) with the same spread. Bottom: the solid blue curve (scale left) is the difference in probability and the dashed red curve (scale right) is the percentage change.

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Figure 2.

For a 1 SD (5.6°C) shift in the distribution (due to climate change) from A to B, only values of B to the right of the two‐tailed 5% significance level (α = 0.05 in red) would be considered significant under a null hypothesis of no change. All the values in the blue area of the B distribution would not.

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Paleoclimates and Current Trends > Detection and Attribution
Climate Models and Modeling > Knowledge Generation with Models

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