East African rainfall due to natural cycles in Indian Ocean, not due to man made CO2-Nature Magazine

1/17/13, "Multidecadal variability in East African hydroclimate controlled by the Indian Ocean," Nature Magazine

"Editor's Summary: Factors causing the East African drought"

"The recent calamitous drought in East Africa was severe in part because it was superimposed on a persistent, decadal-scale decline in spring rainfall. Attempts to understand the mechanisms responsible for hydroclimate variations — and thus food security — in the region have been compromised by the brevity of the instrumental record, which makes it difficult to tease out their influences on multidecadal timescales. Here Jessica Tierney et al. present a palaeoclimate synthesis and model simulations for the past millennia, showing that that sea-temperature variations in the eastern Indian Ocean — rather than the Pacific — are the dominant long-term influence on East African rainfall. 

Cool conditions in the Indian Ocean set up a local atmospheric circulation that favours ascending conditions and higher precipitation."

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Nature study on East African rainfall:

"The recent decades-long decline in East African rainfall¹ suggests that multidecadal variability is an important component of the climate of this vulnerable region. Prior work based on analysing the instrumental record implicates both Indian² and Pacific¹ ocean sea surface temperatures (SSTs) as possible drivers of East African multidecadal climate variability, but the short length of the instrumental record precludes a full elucidation of the underlying physical mechanisms. Here we show that on timescales beyond the decadal, the Indian Ocean drives East African rainfall variability by altering the local Walker circulation, whereas the influence of the Pacific Ocean is minimal. Our results, based on proxy indicators of relative moisture balance for the past millennium paired with long control simulations from coupled climate models, reveal that moist conditions in coastal East Africa are associated with cool SSTs (and related descending circulation) in the eastern Indian Ocean and ascending circulation over East Africa. The most prominent event identified in the proxy record—a coastal pluvial from 1680 to 1765—occurred when Indo-Pacific warm pool SSTs reached their minimum values of the past millennium. Taken together, the proxy and model evidence suggests that Indian Ocean SSTs are the primary influence on East African rainfall over multidecadal and perhaps longer timescales."
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Further comment on the East African rainfall study:

2/23/13, "</sup>East African Drought Due To Natural Cycles – Not Man-Made, Study In Nature Shows," P. Gosselin, No Tricks Zone 

"A new publication in the journal Nature casts serious doubt on the supposed man-made East African drought assumption. US scientists from Woods Hole Oceanographic Institution and Lamont-Doherty Earth Observatory, led by Jessica Tierney, have taken a closer look at moisture trends in East Africa and have uncovered a surprise. Using geological reconstructions, the scientists were indeed able to confirm that East Africa has dried out during the past decade. However, the group also succeeded in reconstructing the data all the way back to the year 1300....

Jessica Tierney and her team started looking for a natural driver for East Africa’s moisture development. They compared the drought data with the temperature development in the Indian Ocean. Lo and behold: both curves showed a high degree of similarity. Obviously the rain in East Africa is driven significantly by the Indian Ocean. Whenever the India Ocean is cool, the rains in East Africa increase. And when the Indian Ocean is warm, the rains become more seldom."... (charts at link) via Tom Nelson



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