Tuesday, May 25, 2010

The Ice Age Was Probably Something Like This

Late spring has been unusually cool in California, as well as inland in the Great Basin. As a result, snowmelt has been slower than usual.

I recall that Donald K. Grayson's book "The Desert's Past", which is all about the natural history of the Great Basin, featured a discussion to the effect that the kind of weather that led to the growth and development of lakes in the Great Basin during the Ice Ages is a subset of the current climate of the Great Basin. You don't need a truly dramatic change in climate to bring the Ice Age lakes back. Nothing so dramatic as the "The Day After Tomorrow". Grayson discusses the findings of Larry Benson:
Today, evaporation rates in the Lahontan Basin are on the order of 48" a year. What if the 1983 water inflow figures were combined with the lowest monthly evaporation rates known to have occurred during historic times? Those lowest known rates yield 24.8" of evaporation a year, roughly half the the average amount. Given the 1983 inflow rates (2.5 times the average) and the minimum monthly evaporation rates (about 0.5 times the average) Benson showed that Lake Lahontan could, in fact, reappear.
Grayson then relates that Benson suggests that the mean annual temperature decrease known to have occurred during the Pleistocene, of 9 to 13 deg F, would be required to bring Lake Lahontan back.

There is evidence that the Laurentide Ice Sheet's presence in the Ice Age led to a split in the jet stream that brought cooler temperatures and more rains to California and the Great Basin during the Ice Age ("Climatic Changes of the Last 18,000 Years: Observations and Model Simulations," COHMAP MEMBERS, Science, 1043-1052, August 26, 1988).

Aerial pictures might do justice to the topic, but at least at the Stillwater Refuge near Fallon, NV, water levels appear to be up. If we could just keep the weather like this for an extended period, Lakes Lahontan and Bonneville might slowly reappear before our eyes!

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