Abstract
In climate change science the term ‘Arctic amplification’ has become synonymous with an estimation of the ratio of a change in Arctic temperatures compared with a broader reference change under the same period, usually in global temperatures. Here, it is shown that this definition of Arctic amplification comes with a suite of difficulties related to the statistical properties of the ratio estimator itself. Most problematic is the complexity of categorizing uncertainty in Arctic amplification when the global, or reference, change in temperature is close to 0 over a period of interest, in which case it may be impossible to set bounds on this uncertainty. An important conceptual distinction is made between the ‘Ratio of Means’ and ‘Mean Ratio’ approaches to defining a ratio estimate of Arctic amplification, as they do not only possess different uncertainty properties regarding the amplification factor, but are also demonstrated to ask different scientific questions. Uncertainty in the estimated range of the Arctic amplification factor using the latest global climate models and climate forcing scenarios is expanded upon and shown to be greater than previously demonstrated for future climate projections, particularly using forcing scenarios with lower concentrations of greenhouse gases.
Highlights
DiscussionAn important distinction exists between the various analyses of Arctic amplification made so far; and that is whether they are considering changes in temperature as an equilibrium or transient climate response
Note that the dimensions of the confidence intervals were largely insensitive to the choice of ρg,a used, within the scope of the results given by the various observational datasets
Summary
An important distinction exists between the various analyses of Arctic amplification made so far; and that is whether they are considering changes in temperature as an equilibrium or transient climate response. Polar amplification exists where horizontal heat transport between polar and equatorial regions causes a latitudinal difference in temperature distribution that would not be predicted by local net radiation balances. Polar amplification exists where horizontal heat transport between polar and equatorial regions causes a latitudinal difference in temperature distribution that would not be predicted by local net radiation balances45 Considering this physical definition of amplification, a latitudinal difference in temperature changes perhaps seems more relevant to studies focusing on Arctic (or polar) amplification than using either hemispheric or global temperature changes as a reference. One way to distinguish the Arctic and tropical regions could be based on either side of where the (annually or seasonally) averaged meridional wind component v is equal to 0 This would at least allow the data-set or climate model to more decide where the higher and lower latitude regions lie
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