Abstract
Abstract. The climate response of the Earth to orbital forcing shows a distinct hemispheric asymmetry due to the unequal distribution of land in the Northern Hemisphere versus Southern Hemisphere. This asymmetry is examined using a global climate model (GCM) for different climate responses such as mean summer temperatures and positive degree days. A land asymmetry effect (LAE) is quantified for each hemisphere and the results show how changes in obliquity and precession translate into variations in the calculated LAE. We find that the global climate response to specific past orbits is likely unique and modified by complex climate–ocean–cryosphere interactions that remain poorly known. Nonetheless, these results provide a baseline for interpreting contemporaneous proxy climate data spanning a broad range of latitudes, which may be useful in paleoclimate data–model comparisons, and individual time-continuous records exhibiting orbital cyclicity.
Highlights
The arrangement of continents on the Earth’s surface plays a fundamental role in the Earth’s climate response to forcing
The Northern Hemisphere (NH) experiences elevated summer insolation, but the response is attenuated by the interhemispheric effect
If precession is considered in isolation, according to the astronomical theory of climate the NH should experience “interglacial” conditions when perihelion coincides with NH summer
Summary
The arrangement of continents on the Earth’s surface plays a fundamental role in the Earth’s climate response to forcing. Due to the asymmetric global geography of the Earth, more continental land area is found in the Northern Hemisphere (NH; 68 %) as compared to the Southern Hemisphere (SH; 32 %) These different ratios of land vs ocean in each hemisphere affect the balance of incoming and outgoing radiation, atmospheric circulation, ocean currents and the availability of terrain suitable for growing glaciers and ice sheets. By comparing the climates of the NH and SH, and the distribution of land and sea, Lyell pointed out that the present continental distribution lowers high-latitude temperatures in both hemispheres. He further pointed out that dominance of ocean in the SH leads to mild winters and cool summers. Lyell’s work is significant in the context of this paper because it first sparked the debate of continental forcing versus astronomical forcing of climate
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