The impact of 21^st century climate change on African agriculture deserves special attention, considering rapid population growth and the fact that the continent is currently already a net importer of agricultural products, while several sub-Saharan countries still depend for a third to over half of their GDP on agricultural output.

Climate change poses an additional stress for these highly dependent nations: for 5 of the 7 most important sub-Saharan food staples (maize, sorghum, millet, groundnut, and cassava) already by the year 2050 significant productivity reductions are expected – decreasing average production between ±22 and ±8 percent, per respective crop:

Climate change is set to decrease net agricultural productivity for major food staples in Africa (crops in rows, mean model estimate in central panels).

This we learn from a 2010 publication in Environmental Research Letters, performed by Wolfram Schlenker and David Lobell, researchers from Columbia and Stanford University that have modelled future agricultural yields using historical productivity changes from observed climatic fluctuations.

We’ll get back to the study in a bit, but first a background context to the expected effects of climate change for Africa, over the course of the current century:

A short summary of climate change in Africa

In previous posts we’ve paid ample attention to the specific effects of climate change to Africa – one of the areas on Earth that, despite lying far away from the poles and being bordered by two oceans without protection of serious mountain ranges, is still expected to experience above average temperature rise over the course of the 21^st century, the extent of which depends on latitude and more so on future emissions:

According to IPCC AR5 African average temperatures have already gone up by between 1 tot 1.5 degrees between 1901 and 2012 and are set to experience an additional 21^st century warming of around 1.5 degrees under the most ambitious RCP2.6 emissions scenario, up to an additional 21^st century warming of 4 degrees for the tropics and 5 to 6 degrees for the subtropics under business as usual emissions (RCP8.5 scenario).

As a result evaporation is going up (fuelling drought risk) while in addition Africa is set to experience major precipitation changes that are partly skewed. On average tropical rainfall will increase and subtropical rainfall may decrease (“wet regions become wetter, dry regions drier”), but especially in East Africa precipitation is modelled to become more capricious, increasing seasonal flood risk from the Eastern Sahel to Tanzania, while the Congo Basin (in line with Amazonian droughts) may actually partially dry out from the southwest.

Of course these climatic changes will have major ecological effects, tipping the borders between desert, savanna and rainforest and thereby forcing entire biomes to switch state – endangering all species that cannot keep up.

More people, less food? Most important staple (maize) set to decline sharpest!

But what about the effects on humans? For Africa a direct concern is the effect of climate change on agriculture – for two important reasons: economy and food supply, as we illustrated yesterday – whereby these climate impacts are gravely exacerbated by population growth: another quadrupling of human inhabitants over the course of the century, dwarfing the population growth on other continents.

The Environmental Research Letters publication looked at 5 of the 7 the most important domestically produced food staples for Africa: maize, sorghum, millet, groundnut, and cassava – excluding the remaining two, which are rice and wheat – because these are irrigation-depending crops, an artificial situation that is more difficult to assess under a nature-mimicking climate experiment. The researchers also experienced difficulty assessing climate impacts on cassava productivity, because casava “is continuously harvested and therefore has a poorly defined growing season and production year, resulting in a poor model fit”.

Based on FAO figures, the top sources of calories for sub-Saharan Africa as a whole are, in order, maize, cassava, rice, sorghum, wheat, and millet – so in this study the projected decline of productivity for maize (well-modelled) as the number 1 food staple deserves special attention. And according to the authors maize shows the sharpest decline, with an average estimate of -22 percent by mid-century. [We have to bear in mind that for Africa both population growth and climate warming are projected to continue between 2050-2100 and even beyond.]

The impact of climate change on food staples in Africa. Note that increasing heat stress is the main concern.

The confidence interval for the decline per crop is illustrated in the above box plot that shows another interesting aspect: it is temperature rise that leads to productivity declines, not precipitation changes.

From a certain temperature onwards, heat really becomes a killer…

© Rolf Schuttenhelm | www.bitsofscience.org