Countries, particularly developing countries, with arid and semi-arid areas or areas that are subject to floods, drought and desertification are especially vulnerable to the adverse effects of climate change. Scientists cannot yet predict how climate change will affect the global rate of desertification. However, the predicted changes in temperature, evaporation, and rainfall from region to region are likely to aggravate desertification in some critical areas but may ease it in other places.
The degree to which the desertification of the last few decades has been influenced by climate change is open to debate. It is clear that other mechanisms, particularly deforestation and agricultural practices, are major influences. However, there is general agreement that climate change will change rainfall distribution and amount, and where reduced precipitation coincides with present-day arid areas, the propensity for and speed of desertification in those areas will increase.
Desertification has been a long-standing problem in many areas of the world. It is particularly pronounced in Africa, where Mauritania provides an extensively studied example, where it has been found that:
The climate has altered drastically since the onset of the prolonged drought in the 1960s, part of a recurrent pattern of wet and dry cycles common to Sahelian Africa. Experts agree, however, that overgrazing, deforestation, denuding of ground cover around wells, poor farming methods, and overpopulation have aggravated the drought. In Mauritania the isohyet [geographic line of constant rainfall] indicating annual rainfall of 150 millimeters—considered the minimum for pastoralism—has shifted southward about 100 kilometers. During the 1980s, the desert was advancing southward at an estimated rate of six kilometers a year. Each major climatic zone had shifted southward.
Source: Robert E. Handloff, ed., 'Expansion of the desert', Mauritania—a country study, GPO for the Library of Congress, Washington, 1988.
In China, the Kumtag desert is expanding by one to four metres eastward annually. In southern Europe, desertification and related loss of productive capacity has worsened considerably over the last few decades. One study projected an average precipitation decline of 22 per cent with a doubling of carbon dioxide, while the probability of a 30-day dry spell increased two to five times.
Degraded land tends to hold less surface moisture. This means that of the sun's energy reaching the surface, less goes into evaporation of water and more goes into heating the surface. This heat is then transferred to the air in the lower atmosphere. In addition, more dust and other particulates are released into the atmosphere from drylands eroded by winds. The feedbacks between these AEROSOLS and climate are complex, and can produce both cooling and warming effects depending on their location in the atmosphere and their interaction with clouds.
The Fourth Assessment Report of IPCC noted that desert biodiversity is susceptible to climate change, particularly plants and animals dependent on winter rainfall. Combined with land-use pressures, climate change is expected to lead to increased desiccation of already dry areas, and exacerbate soil loss.
Intergovernmental Panel on Climate Change, Working Group I Contribution to the Fourth Assessment Report, Climate change 2007—the physical science basis, Chapter 3, Observations—surface and atmospheric climate change, Section 3.3.4, 'Changes in soil moisture, drought, runoff and river discharge'.
United Nations Framework Convention to Combat Desertification.
United Nations Framework Convention on Climate Change, Climate change—impacts, vulnerabilities and adaptation in developing countries, 2007.