Climate change in southern Africa: what to expect and what to do

Much has been said and written about climate change. But how will it affect southern Africa specifically?

First things first: how do we know that the climate has changed? The thermometer and the barometer were invented in the 17th century, so there’s been a substantial amount of time during which we’ve been taking temperature measurements and, in southern Africa, the general trend has been a gradual warming over the past century.

If you take all the data over the last 50 or 60 years, and you look at the warmest and coldest temperatures, there were more of the coldest nights in 1960 than in 2012, and there were more of the warmest nights in 2012 than in 1960. If you look at the daytime temperatures, it’s exactly the same – the change is away from cool, towards warm.

What about precipitation? Trying to get data for extreme precipitation is very, very difficult because extreme weather events don’t happen very often. As a statistician, you would need a long time period of measurements in order to extract the truth, and we don’t have this. But we can pick out extreme weather events from the last 10 to 15 years. There are floods in Europe right now; we had the Oklahoma tornadoes in the United States (US) in the last few weeks; we had Hurricane Sandy hit New York and Hurricane Katrina hit the southern states of the US; and we’ve had major floods in Australia and Southeast Asia in the last few years.

In southern Africa, the link between drought and the El Nino phenomenon in the Pacific is particularly significant. El Nino – which shifts the winds, the sea surface temperatures and the weather patterns – has impacts around the world and the El Nino events of 1991 to 1992, and again in January to March 2007, gave rise to significant droughts in southern Africa.

It’s hard for scientists to say whether any of this is related to climate change or whether it’s just natural variability, but it’s quite clear that there have been extremes recently and there is a general sense that they are becoming more frequent.

Sea level rising

We can also look at the rise in sea level as there are stations all along the coastlines, which measure tides and sea level. We have measurements beginning from about 1980 and the main concern is that the sea level has been rising at a faster and faster rate; in fact, lately it has been increasing by three millimetres per year.

Now, this is a very small amount and you may say: who cares? But remember that’s the mean level; it doesn’t account for the waves and the tides. Also, after a century or more, you’re talking about a substantial amount. This increase in the volume of the oceans is due to the melting of ice caps and glaciers, mainly in the North Pole.

To investigate climate change over longer periods of time, one can look at tree rings. Some trees grow a single ring every year and the depth, composition and colour of the rings can be interpreted in terms of temperature and precipitation during the lifetime of the tree. You can do that for a few thousand years because some trees have had very long lives. You can also look at artwork – especially paintings of northern Europe which indicate that, a few hundred years ago, rivers usually froze during the winter. In Africa, rock paintings from the Sahara indicate that this desert used to be a savannah.

Putting all these pieces together you can reconstruct an evolution of temperature over the last thousand years or so (the famous hockey stick diagram). There has been a lot of variability, but certainly the temperature of the planet is now increasing at a rate way beyond what it has ever done before.

In fact the temperature of this planet is changing so fast that we are considering worrying that the biosphere – plants and animals, and perhaps even human societies – might not be able to adapt fast enough and that some species may actually disappear.

More questions than answers

So how will climate change affect southern Africa? The answers are not yet clear.

First, we don’t know what’s going to happen in the future because it’s mostly up to us. We can choose how much fuel we burn, how much air travel we do and how often we drive our cars, so the amount of CO2 in the atmosphere will depend on the choices we make, and the choices our governments make.

Other factors are variable, particularly the impact of aerosol – the small particulates that come mainly from industrial production. There’s been a huge increase in aerosol, particularly over areas that have been rapidly industrialising – China, India, and Brazil.

What we do with the land: whether we chop down all the trees in a forest – will also have an impact on the climate. All these things add a degree of uncertainty. On top of all that, there’s the fact that the climate is not static – it is changing naturally all the time.

By the time we’ve taken all those uncertainties into account, we really can’t be sure about the future. But it’s important enough for us to make our best estimate. So scientists have constructed predictions for three different scenarios based on a range of climate models, which have been brought together.

If we look at the overall picture, by the time we get to the end of the century, everywhere in the world will be much warmer. In southern Africa, the same theme emerges. Inland, we can expect temperatures to rise by the end of the century by about three to four degrees. The change will be a little less on the coast and over the oceans.

Predictions for precipitation are not quite so clear. The predominant expectation is for rainfall to decrease, particularly in the far west where the models indicate about a 20 percent reduction in precipitation. This is clearly concerning, particularly for agriculture.

The general consensus around crop yields is that there could be an issue around some of the staple food crops in southern Africa, particularly maize and wheat, but on the other hand there are some crops for which the yield might actually rise, such as rice and groundnut. The possibility exists that nearly all croplands might experience early and sustained declines in suitability, even under the best-case scenario.

A significant variable is whether we’ll be able to irrigate, bearing in mind we’re facing up to a 20 percent decrease in precipitation in some places by the end of the century. If we don’t irrigate then we’ll end up with some significant negative figures for percentage changes in yield.

Another variable is the ability of the soil to sustain growth, or the impact of temperature and moisture on particular types of soil. With climate change, soil that is currently perfect for growing a particular crop will become progressively less so with time.

Lower yields to come

To summarise, of the few studies that have been done, there’s a general signal that for some of the staple food crops in southern Africa, the yields will decrease. If we can still irrigate then we can probably get around a lot of the problem, but for natural, un-irrigated food production, it’s likely that the soil will become less and less suitable for the types of crops that are being grown at present and there’ll be a need for some kind of adaptive change in agriculture.

From crop yields we move to the wider question of food security and the summary for southern Africa is that, compared to other parts of Africa, there won’t be a huge issue with undernourishment. Although crop yields may significantly decrease, southern Africa may be able to almost completely offset any increase in exposure to undernourishment due to climate change by structural adjustment; in other words, by diverting food from exports to local consumption.

Over the next 100 years, there is likely to be a decrease in food availability for up to 100 million people who will be undernourished if we do nothing about it. But by reducing exports, you can bring that massive number right back down to zero again. So what reports are saying is that there will be less food to go around, but if we don’t give it to someone else, then there will still be enough for us to eat. Of course, if you reduce exports, there will be an economic impact and that brings up planning issues in terms of how to sustain the economy.

Moving from food to water, what does a decrease in precipitation mean for water availability? There will be an impact, but it will be relatively minor compared to other parts of the world. By 2050 southern Africa will still have enough water to go around, but many parts of the world will not.

A question to consider is: if we’re okay here, but other parts of Africa are in serious trouble, is that okay? We live in a global village and if there’s a problem elsewhere, sooner or later it will impact us wherever we are.

In terms of flood risk, despite the likely decrease in average precipitation, the intensity of precipitation when it happens is likely to go up. So in areas that normally experience heavy rain, it will be heavier than it was before, with an increased chance of flooding. There’s also a danger of flooding from the sea, and Cape Town is one of the key cities that is vulnerable and needs to have some adaptive measures to protect it from increased risk of storm damage and coastal flooding.

There’s a huge amount of uncertainty around precipitation in southern Africa. Essentially a fairly small number of people, in global terms, are at risk of coastal flooding, but up to maybe a third to a half of the wetlands around the coast of southern Africa are at risk of flooding due to a rise in sea level.

In summary, we have observed significant warming over the last 50 or so years and there’s every reason to believe that it’s a result of human action. As we project ahead, we see temperatures increasing by about three or four degrees in southern Africa – and clearly that will have a wide range of impacts. There’s likely to be an impact on crop yields, especially where there’s no irrigation, and that will have an impact on food security and possibly introduce a need for changes in policies around exports. It will also have an impact on water security and flood risk which, for this part of the world, will be relatively modest.

But there are many uncertainties. Part of the answer is for scientists to carry on working to clarify the uncertainties and give us a clearer picture. But in the meantime, in terms of policy, the fact that something is uncertain is no reason to not act. We have to consider the risks and make the best decisions at any particular time.

It’s all very well to look at southern Africa in isolation, but we live in a global village and if there are bigger impacts going on in other parts of the world, we can’t expect southern Africa to be immune.

– The Global Change and Sustainability Research Institute (GCSRI) at the University of the Witwatersrand recently hosted Michel Verstraete from the European Commission Joint Research Centre and Dr Rob Varley from the United Kingdom Met Office for a seminar entitled “Climate change in southern Africa: What to expect and what to do”. This article is based on their lectures. For more information go to
www.wits.ac.za/news.