Turbulent Times

A major concern in this part of the world is the failure of the maize harvest in the South West of Western Province. A local Mwandi District Ministry of Agriculture and Livestock report has looked at the impact of the severe dry spell in the district and identified priority needs and interventions.  90% of subsistence farmers are affected. There is a lack of both surface and ground water due to non-inundation of flood plains from the Zambezi River and its tributaries. This has challenged dependent households and livestock with high commodity prices, the collapse of local markets and the selling of household assets to buy food.

The main findings:

·         85% of rain-fed maize and drought tolerant crops have failed. 

·          3,800 households (21,800 people) will need food aid for 9 months.

·         There has been a significant increase in the prices staple food in the affected areas.

·         Income from crop based and agricultural paid labour to address any food deficit is unavailable.

·         The internal migrations to the Zambezi fishing camps and island pastures will happen much earlier and in greater numbers due to a lack of grazing and water in the hinterland.

The local areas most affected are Mabumbu, Sankolonga, Kamusa and Adonsi. The main environmental problems in our area stem from an increase in population leading to deforestation, monoculture on poor soil and overgrazing.

With much loud, political scepticism abroad, climate scientists tend to be very cautious about attributing specific weather events to global warming. The variability of weather makes it difficult to know whether climate change caused any particular drought, flood, heatwave or storm. An article in this week’s Economist called, “Is It Global Warming Or Just The Weather?” dealt, I thought, with the matter fairly and objectively and is of interest to us in the midst of our drought.

Much of the debate has focused on the rise of global mean surface temperatures by 2100. That is the simplest way to measure the long-term impact of climate change, but it has drawbacks; it takes measurement over a century. While most people worry about local temperatures not global ones, and try to link climate change to their local weather, not just increases in the mean temperatures, but also in the extremes which often have a more profound local impact on people.

It is still not possible to say categorically that climate change has caused any individual storm, flood, drought or heatwave, but scientific attribution does not require certainty; it deals in probabilities. Most rational people now link smoking to lung cancer, similarly we can say climate change increases the risk of a particular weather pattern by a measurable amount and, in some cases and that even a particular episode is almost impossible to imagine without global warming. That is as near as you can get to saying global warming caused a weather event. Contributions to climate change can be calculated by looking at what the climate would have been like if people had not increased greenhouse-gas emissions. That means comparing observations of the weather with computer models of what might have happened without climate change. So you can calculate the probability of a weather pattern occurring. So it is now possible to say that man-made climate change made this or that weather event twice as likely, five times more likely, or less likely and there is now a scientific consensus that humans are largely responsible for climate change. The strongest evidence for human influence can be seen in some heatwaves, where human influence increased the risk of such high temperatures fivefold, at least. Some heatwaves would have been “virtually impossible” without climate change.

Studies of recent heatwaves in in Europe, Australia China, Japan and Korea. All showed that man-made climate change had increased the likelihood of exceptional heat. This resulted in changes to ocean currents and the great Arctic melt, and to emissions of greenhouse gases and aerosols. However, some like the melting of Arctic ice, are influenced by natural variability as well.

Climate change also seems to be contributing to droughts, though the evidence here is weaker. Higher temperatures speed up evaporation, reduce soil moisture and lead to drought. Increased greenhouse-gas emissions are also a factor, as are other sorts of human influence, such as population growth and water consumption. Of four recent studies of droughts, two clearly showed that man-made influences were increasing the risk.

The evidence is weaker still when it comes to storms. It is often said that climate change is making hurricanes and other heavy storms more frequent but recent studies found no evidence of human influence in any of them.

A Swiss study into heatwaves and rain storms took all the heat and precipitation extremes between 1901 and 2005, defining extremes as events likely to occur once every 1,000 days. They found that 0.85°C of warming (the rise since the industrial era began) has made such heat extremes four or five times more likely. 75% of the heat extremes, and 18% of the precipitation extremes, were attributed to global warming and the probability of a heat extreme is twice as great at 2°C of warming than at 1.5°C.

That does not mean, alas, that the science of weather attribution will be able to forecast particular droughts or heatwaves, only to say that more of them are likely to happen. That is a useful addition to climate science. People are routinely told about—and routinely ignore—the bad things they are doing to the climate. The attribution studies show that the climate is doing bad things back.