A Test for Nonlinearity in Temperature Proxy Records

Abstract

re temperature proxy records linear recorders of past temperature conditions? A statistical test for linearity is applied to 15 millennial-long proxy records with an annual resolution that was shown to significantly respond to Northern Hemisphere annual mean temperature selected from a collection of 30 proxies. The test, based on generalized additive modeling, shows that most of the proxies can indeed be shown to be linear functions of annual mean temperature, but two proxy records do not appear to have a linear relationship with temperature?this supports the assumption of linearity in most climate reconstruction work. The method tests for nonlinearity in a proxy relative to the group of proxies with which it is being used together. The robustness of the results is tested, and it was found that the results are stable to the choice of proxies. The linearity-testing method is quite general and could in the future be used for larger and more extensive sets of proxies.