A new hypothesis for the 1470-year cycle of abrupt warming events in the last ice-age

In this thesis, a new hypothesis is presented for the glacial 1470-year climate cycle, which manifests itself in abrupt warming events (the socalled Dansgaard-Oeschger events, or DO events). According to the hypothesis, two century-scale solar cycles could explain the regularity in the timing of the DO events, since the periods of these two cycles are close to integer factors of 1470 years. This hypothesis is tested with a coupled climate model of intermediate complexity. It is shown that abrupt warming events, which reproduce many features of the DO events (in particular their time scale of 1470 years), can occur in the climate model in response to two centennial-scale freshwater cycles, with periods close to those of the two known solar cycles. The plausibility of these model results is tested with a very simple conceptual model, in which DO events represent abrupt switches between two modes of the thermohaline ocean circulation. It is shown that the millennial-scale response of the climate model to the century-scale forcing is a plausible consequence of the high degree of non-linearity and the large characteristic time scale of the thermohaline circulation. As a result, the glacial 1470-year climate cycle might indeed be caused by the Sun, despite the lack of a corresponding solar frequency