The following blog post is contributed by Philip Thornton (pictured middle above), theme leader and senior scientist with the Challenge Programme on Climate Change, Agriculture and Food Security  at the International Livestock Research Institute (ILRI) in Nairobi, Kenya and an honorary research fellow in the Institute of Atmospheric and Environmental Sciences at the University of Edinburgh. Thornton has worked mostly in Latin America, Europe, North America and Africa on systems modelling and impact assessment. His current research interests revolve around integrated assessment at different scales and evaluating the possible impacts of global change on agricultural systems in developing countries.

The Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) is in trouble again. A posting by a guest blogger published recently in the Christian Science Monitor (13 October 2010) quotes the following statement in the summary report of the Fourth Assessment Report (AR4): ‘. . . Additional risks that could be exacerbated by climate change include greater erosion, deficiencies in yields from rain-fed agriculture of up to 50% during the 2000–20 period, and reductions in crop growth period (Agoumi, 2003).’

The guest blogger in the Christian Science Monitor, G Pascal Zachary, uses this reference as an example of how scientists are ‘exaggerating’ claims about possible catastrophic declines in African food production in this century, leaving the reader with the impression that everything is dandy in the garden of Africa’s response to climate change.

What are we to make of this? In my view, two serious breakdowns in communication have occurred.

The first breakdown relates to the quote from Agoumi, from an article published in 2003, itself. Although its precise meaning may not be completely clear, it’s obviously been taken to mean in the IPCC summary report that ‘yields in Africa will decrease by 50% by 2020’, whereas I suspect a more faithful interpretation of the meaning of Agoumi’s quoted statement is that climate change may increase the probability that some countries in North Africa, which Mr Agoumi was referring to, may get a yield reduction of 50% in some places in some years. This is not surprising—there are many rain-fed, marginal environments in Africa where yield reductions of 50%, against a long-term mean, may occur in certain years. I suspect Agoumi was simply saying (admittedly somewhat unclearly) that this probability would increase, for example, from 1 year in 4 to 1 year in 3. Whether this is a true probability statement or not, I don’t know. But it’s pretty likely that the IPCC summary report itself has misinterpreted his quotation.

The second serious breakdown in communications relates to how this is interpreted by the Christian Science Monitor‘s blogging correspondent, Zachary, an American writer, teacher and researcher who blogs at Africa Works, and whose interpretation is probably shared by many others. We might characterize the problem as similar to the following. In the city where I live, some of the bus-stops have electronic information screens that tell you when the next bus is coming. One day I go to catch a bus to town. Before I leave the house, I consult the on-line timetable of the bus company, which says one is due at 4 pm. When I walk around the corner to catch it, the electronic scoreboard says it is due at 4.10 pm. As it happens, I am still waiting at 4.15 pm–no bus!  So do I conclude that the bus is not coming at all? No, of course not. It turns out that it arrives at 4.20 pm. OK, it’s late, and later than the electronic system said. But come it does.

This experience seems to me similar to that of reading projections of the impacts of climate change on African agriculture. There is a lot of uncertainty in climate model projections—none of the different climate models can simulate El Niño very well, or the impacts of certain Indian Ocean effects on East Africa’s weather, for example, but there is now such a large amount of evidence, using all sorts of different techniques (which didn’t exist in 2003 when Agoumi made his statement or in 2006 when the IPCC summary report was being put together), that we know that African crop yields, overall, are going to be reduced a great deal because of climate change, all other things being equal. We can choose 50% as a reduction factor, if we like; the question is not ‘Will it occur?’ (it will), but ‘By when will it occur?’ And in answer to this, we can assert with high confidence: during the second half of the current century.

The issue of climate change and African agriculture cannot be left entirely to African farmers’ undoubted skills in risk management. Climate changes in the next few decades will make agriculture in many places in Africa completely unlike anything Africa’s farmers, even their great-grandparents, have experienced. The knowledge and skills built up in communities in Africa over the millennia are simply not going to be enough to deal with the scale of the changes that we know are going to come about.

What we don’t know is exactly when a given level of farm yield reduction will occur. But my feeling is that our climate change research to date probably is under-estimating, not over-estimating, the magnitude of the changes, for various technical reasons. We’re not able to take fully into account the impacts of changing weather variability on agricultural yields, for example, and we don’t know much about the future dynamics of pest, weeds and diseases. We suspect the bus is going to arrive earlier rather than later—but whenever it does, it is certain to bring devastating yield changes with it.

For all the uncertainty in climate science, a strong evidence-based consensus is emerging as to the (large and increasing) magnitude of the climate changes we shall face in this century and beyond. Africa as a whole, over the next few decades at least, will be among the regions least able to cope with, and adapt to, climate changes because most of its people still rely on the weather directly to support their agricultural livelihoods and most of these farming households are widely dispersed and unserved by information and infrastructure. Scientists have not done nearly enough to wake up the general public to the severity of the changes that Africa will be facing in this century.

In brief, not much could be further from the truth than the Christian Science Monitor‘s headline assertion that ‘Africa’s food security is less threatened than many fear’.

Read Zachary’s blog post, Africa’s food security is less threatened than many fear, 13 October 2010.