Meteorologist Jeff Masters’ discussion of atmospheric circulation, global warming, and climate modelling in the context of a massive weather disaster, the recurrent East African drought, seems to me to be moving towards the kind of interdisciplinary thinking needed to grapple with climate change. Perhaps meteorologists are now needed to warn society at large about deeper issues than whether we are going to get wet during our evening commute or even warning us that a tornado is about to hit our town.
To channel Nietzsche: the distinction between meteorology and climatology must be overcome! Weather and climate are not ontological categories – simply put, they are not real in the same way as clouds or wind. They are epistemological categories used to scientifically understand clouds and wind at scales we do not encounter in our everyday lives. Perhaps by recognizing this, we can better use them to manage socio-ecological risk and not become captive to their models.
The climate of East Africa during the main March – June rainy season has steadily dried over the past 30 years. Since 2004, six of the past eight years have seen unusually deficient spring “long rains.” This drying of the East African climate has come as the waters of the Indian Ocean have warmed significantly.
A 2011 study by A. Park Williams and Chris Funk of the University of California, Santa Barbara, blames the drought in East Africa on the heating up of the Indian Ocean, which has altered the atmospheric circulation over East Africa to bring more sinking air and less moisture.
The atmospheric circulation over East Africa is part of Earth’s largest atmospheric circulation feature–the Walker circulation. The Walker circulation features rising air over the warmest waters of the Pacific Ocean, and compensating sinking air over over eastern tropical Africa and the eastern tropical Pacific. The Walker circulation also helps drive the El Niño/La Niña phenomena in the Eastern Pacific.
Williams and Funk show that the increase in Indian Ocean temperatures in recent decades has made the Walker circulation extend farther west, resulting in more sinking air over East Africa and thus less rain. Since the increase in Indian Ocean temperature driving this change in the atmospheric circulation shows strong linkages with human-caused global warming, they conclude: ”anthropogenic [human-caused] warming appears to have already significantly altered the Earth’s largest circulation feature and impacted its most food insecure inhabitants.” They predict that East Africa will continue to dry as global warming increases the ocean temperatures in the Indian Ocean, impacting the Walker circulation.
However, eighteen of the 21 models used in the 2007 IPCC report on climate change predict more rainfall over East Africa by the end of this century. These models predict that the Walker circulation will weaken, shifting towards a more “El Niño-like” state, resulting in less sinking air (and thus more rain) over East Africa. Since there is as yet no evidence of this happening, and East African climate has gotten drier in recent years, this may be a case where the large majority of the climate models are wrong.