Major changes in global rainfall patterns accompanied a northward shift of Earth’s thermal equator at the onset of an abrupt climate change 14.6 kya. This northward pull of Earth’s wind and rain belts stemmed from disintegration of North Atlantic winter sea ice cover, which steepened the interhemispheric meridional temperature gradient. A southward migration of Earth’s thermal equator may have accompanied the more recent Medieval Warm to Little Ice Age climate transition in the Northern Hemisphere. As fossil fuel CO 2 warms the planet, the continents of the Northern Hemisphere are expected to warm faster than the Southern Hemisphere oceans. Therefore, we predict that a northward shift of Earth’s thermal equator, initiated by an increased interhemispheric temperature contrast, may well produce hydrologic changes similar to those that occurred during past Northern Hemisphere warm periods. If so, the American West, the Middle East, and southern Amazonia will become drier, and monsoonal Asia, Venezuela, and equatorial Africa will become wetter. Additional paleoclimate data should be acquired and model simulations should be conducted to evaluate the reliability of this analog.
We reconstructed the former ice cap of the Wind River Range, Wyoming, using a glaciological model with scaled modern temperature and precipitation inputs to examine probable climate during the local Last Glacial Maximum (LGM) (or Pinedale glaciation). A key result is that temperature anomalies of - 10 °C, -8.5 °C, -6.5 °C, and -5 °C must compensate respective precipitation values of 50%, 100%, 200%, and 300% that of modern in order for the maximum glacier system to attain equilibrium. In further sensitivity tests, we find that ice-cap area and volume shrink by 75% under a climate forcing 50% modern and 50% LGM. The glacier system disappears altogether in ∼100 years when subjected to sustained modern conditions. Our results are consistent with other interpretations of western U.S. LGM climate, and demonstrate that the Wind River Ice Cap could have disintegrated rapidly during the first phase of the termination. In future work we will simulate glacier-climate evolution as constrained by emerging 10Be moraine chronologies.
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