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A theory of abrupt climate changes: their genesis and anatomy
  • hsienwang ou
hsienwang ou
columbia university

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We combine our previous ice-sheet and climate models to address abrupt climate changes pertaining to Heinrich (H) and Dansgaard-Oeschger (DO) cycles as well as last deglaciation punctuated by Younger Dryas (YD). We posit their common origin in the calving of the ice sheet but differentiate thermal triggers by geothermal-heat/surface-melt in calving inland/marginal ice, the respective sources of H/DO-cycles. The thermal switches would produce step-like freshwater fluxes to endow abruptness to the resulting climate signals characterized by millennial timescale due to the internal ice dynamics. For an eddying ocean, its response to the freshwater perturbation entails millennial adjustment to maximum entropy production, which would cause sudden post-H warming followed by gradual cooling to form the H-cycles, and the above-freezing warmth (hence surface-melt) would calve the marginal ice to generate DO-cycles anchored on the cooling trend to form the Bond cycle. Since there is already ablation of the Holocene icecap, there would be self-sustained DO-cycles, which thus retain the same pacing as their glacial counterparts to resolve this seeming puzzle. This millennial pacing also transcends the deglaciation to account for its observed sequence although the occurrence of YD requires a boost of the freshwater flux by the rerouted continental meltwater. It is seen that by differentiating thermal triggers of the ice calving and incorporating MEP adjustment of the ocean, the theory has provided an integrated account of the genesis of the abrupt climate changes and their deduced anatomies bear strong resemblance to the observed ones, in support of the theory.