Recently, there has been considerable interest in a paper showing that rainfall in the Sahel has increased likely due to sea surface temperature trends in the North Atlantic as compared to the oceans in general. Now Eli is not here to tell you about that paper by Alessandra Giannini, she has done it herself,
and so have others, but a related one that seemingly has snuck in under the radar, "The dominant role of semi-arid ecosystems in the trend and variability of the land CO2 sink", by a large group of authors, including Michael Raupach to whom the paper is dedicated as he died before publication. The paper appeared in Science, 11 May 2015.
The authors show that while the carbon sink is dominated by forests, especially tropical forests, the annual variability (hi Victor) in the carbon sinks is dominated by arid lands such as the Sahel which makes sense, because in wet years, the semi-arid lands will bloom, in dry ones, not much.
The figure to the right requires some explanation. The y axes are percent contribution to the biosphere's net carbon flux from each of the land types listed at the bottom. It is the difference between the global primary production and the respiration. LPJ-GUESS is a biogeochemical vegetation model and TRENDY is a model intercomparison project, go read the paper for details. IAV is the interannual variation.
Semi-arid lands like the Sahel dominate both the trend and the interannual variation, which makes sense, they are on the margin and small differences in weather make a large difference in the amount of vegetation.
The paper points out that in 2011 there was a large increase in the carbon sink, which is attributed to a very wet year in Australia.
As to the future, a large increase in the carbon sink appears when it is cool and wet in the semi-arid regions, a large decrease when it is hot and dry. In general the level of precipitation is more important than the temperature.
Taking this into account bunnies should go back and look at Giannini's video. If the Sahel is wetter, then there will be more primary production of vegetation, but if it is hotter, there will be more respiration and decay. That means more food, a very good thing, but not as much natural carbon sequestration as if it were cooler