Effects of climate change in Africa

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Past 1,000 Years

For full article see Past 1,000 years in Africa

Lamb et al. (2003) provided strong evidence for the hydrologic fingerprint of the Medieval Warm Period in Central Kenya in a study of pollen data obtained from a sediment core taken from Crescent Island Crater, which is a sub-basin of Lake Naivasha. Of particular interest in this regard is the strong similarity between their results and those of Verschuren et al. (2000). The most striking of these correspondences occurred over the period AD 980 to 1200, when lake-level was at an 1,100-year low and woody taxa were significantly underrepresented in the pollen assemblage.

Esper et al. (2007) used Cedrus atlantica ring-width data “to reconstruct long-term changes in the Palmer Drought Severity Index (PDSI) over the past 953 years in Morocco, Northwest Africa.” They report “the long-term PDSI reconstruction indicates generally drier conditions before ~1350, a transition period until ~1450, and generally wetter conditions until the 1970s,” after which there were “dry conditions since the 1980s.” In addition, they determined that “the driest 20-year period reconstructed is 1237-1256 (PDSI = -4.2),” adding that “1981-2000 conditions are in line with this historical extreme (-3.9).” Also of significance, the six researchers note that “millennium-long temperature reconstructions from Europe (Buntgen et al., 2006) and the Northern Hemisphere (Esper et al., 2002) indicate that Moroccan drought changes are broadly coherent with well-documented temperature fluctuations including warmth during medieval times, cold in the Little Ice Age, and recent anthropogenic warming,” which latter coherency would tend to suggest that the peak warmth of the Medieval Warm Period was at least as great as that of the last two decades of the twentieth century throughout the entire Northern Hemisphere; and, if the coherency is strictly interpreted, it suggests that the warmth of the MWP was likely even greater than that of the late twentieth century.

In light of these research findings, and many others, it appears that (1) the Medieval Warm Period did occur over wide reaches of Africa, and (2) the Medieval Warm Period was probably more extreme in Africa than has been the Current Warm Period to this point in time.

Precipitation Trends

For full article see Precipitation trends in Africa

The dry episode of the late eighteenth/early nineteenth centuries recorded in Eastern Africa has also been identified in Western Africa. In analyzing the climate of the past two centuries, Nicholson (2001) reports that the most significant climatic change that has occurred “has been a long-term reduction in rainfall in the semi-arid regions of West Africa,” which has been “on the order of 20 to 40% in parts of the Sahel.” There have been, she says, “three decades of protracted aridity,” and “nearly all of Africa has been affected … particularly since the 1980s.” However, she goes on to note that “the rainfall conditions over Africa during the last 2 to 3 decades are not unprecedented,” and that “a similar dry episode prevailed during most of the first half of the 19th century.”

The importance of these findings is best summarized by Nicholson herself, when she states that “the 3 decades of dry conditions evidenced in the Sahel are not in themselves evidence of irreversible global change.” Why not? Because an even longer period of similar dry conditions occurred between 1800 and 1850, when the earth was still in the clutches of the Little Ice Age, even in Africa (Lee-Thorp et al., 2001). There is no reason to think that the past two- to three-decade Sahelian drought is unusual or caused by the putative higher temperatures of that period.

Glaciers

For full article see Glaciers in Africa

For many climate change alarmists, glacial recession at Kilimanjaro served as a warning sign for the type of ecological devastation that anthropogenic global warming would bring if left unabated. Research has shown that this viewpoint is anything but certain.

Citing “historical accounts of lake levels (Hastenrath, 1984; Nicholson and Yin, 2001), wind and current observations in the Indian Ocean and their relationship to East African rainfall (Hastenrath, 2001), water balance models of lakes (Nicholson and Yin, 2001), and paleolimnological data (Verschuren et al., 2000),” Molg et al. say “all data indicate that modern East African climate experienced an abrupt and marked drop in air humidity around 1880,” and they add that the resultant “strong reduction in precipitation at the end of the 19th century is the main reason for modern glacier recession in East Africa,” as it considerably reduces glacier mass balance accumulation, as has been demonstrated for the region by Kruss (1983) and Hastenrath (1984). In addition, they note that “increased incoming shortwave radiation due to decreases in cloudiness—both effects of the drier climatic conditions—plays a decisive role for glacier retreat by increasing ablation, as demonstrated for Mount Kenya and Rwenzori (Kruss and Hastenrath, 1987; Molg et al., 2003a).”

Consequently, Molg et al. concluded that “modern glacier retreat on Kilimanjaro is much more complex than simply attributable to ‘global warming only’.” Indeed, they say it is “a process driven by a complex combination of changes in several different climatic parameters [e.g., Kruss, 1983; Kruss and Hastenrath, 1987; Hastenrath and Kruss, 1992; Kaser and Georges, 1997; Wagnon et al., 2001; Kaser and Osmaston, 2002; Francou et al., 2003; Molg et al., 2003b], with humidity-related variables dominating this combination.”

Clearly, the misguided rushes to judgment that have elevated Kilimanjaro’s predicted demise by CO2-induced global warming to iconic status should give everyone pause to more carefully evaluate the evidence, or lack thereof, for many similar claims related to the ongoing rise in the air’s CO2 content.

Droughts

For full article see Droughts in Africa

Real-world evidence from Africa suggests that the global warming of the past century or so has not led to a greater frequency or greater severity of drought in that part of the world. Indeed, even the continent’s worst drought in recorded meteorological history was much milder than droughts that occurred periodically during much colder times.

Going back in time almost 5,500 years, Russell and Johnson (2005) analyzed sediment cores that had been retrieved from Lake Edward—the smallest of the great rift lakes of East Africa, located on the border that separates Uganda and the Democratic Republic of the Congo—to derive a detailed precipitation history for that region. In doing so, they discovered that from the start of the record until about 1,800 years ago, there was a long-term trend toward progressively more arid conditions, after which there followed what they term a “slight trend” toward wetter conditions that has persisted to the present. In addition, superimposed on these long-term trends were major droughts of “at least century-scale duration,” centered at approximately 850, 1,500, 2,000, and 4,100 years ago. Consequently, it would not be unnatural for another such drought to grip the region in the not-too-distant future.

References

Buntgen, U., Frank, D.C., Nievergelt, D. and Esper, J. 2006. Summer temperature variations in the European Alps, A.D. 755-2004. Journal of Climate 19: 5606-5623.

Esper, J., Frank, D., Buntgen, U., Verstege, A., Luterbacher, J. and Xoplaki, E. 2007. Long-term drought severity variations in Morocco. Geophysical Research Letters 34: 10.1029/2007GL030844.

Francou, B., Vuille, M., Wagnon, P., Mendoza, J. and Sicart, J.E. 2003. Tropical climate change recorded by a glacier in the central Andes during the last decades of the 20th century: Chacaltaya, Bolivia, 16°S. Journal of Geophysical Research 108: 10.1029/2002JD002473.

Hastenrath, S. 1984. The Glaciers of Equatorial East Africa. D. Reidel, Norwell, MA, USA.

Hastenrath, S. 2001. Variations of East African climate during the past two centuries. Climatic Change 50: 209-217.

Hastenrath, S. and Kruss, P.D. 1992. The dramatic retreat of Mount Kenya’s glaciers between 1963 and 1987: Greenhouse forcing. Annals of Glaciology 16: 127-133.

Kaser, G. and Georges, C. 1997. Changes in the equilibrium line altitude in the tropical Cordillera Blanca (Peru) between 1930 and 1950 and their spatial variations. Annals of Glaciology 24: 344-349.

Kaser, G. and Osmaston, H. 2002. Tropical Glaciers. Cambridge University Press, Cambridge, UK.

Kruss, P.D. 1983. Climate change in East Africa: A numerical simulation from the 100 years of terminus record at Lewis Glacier, Mount Kenya. Zeitschrift fur Gletscherkunde and Glazialgeologie 19: 43-60.

Kruss, P.D. and Hastenrath, S. 1987. The role of radiation geometry in the climate response of Mount Kenya’s glaciers, part 1: Horizontal reference surfaces. International Journal of Climatology 7: 493-505.

Lamb, H., Darbyshire, I. and Verschuren, D. 2003. Vegetation response to rainfall variation and human impact in central Kenya during the past 1100 years. The Holocene 13: 285-292.

Lee-Thorp, J.A., Holmgren, K., Lauritzen, S.-E., Linge, H., Moberg, A., Partridge, T.C., Stevenson, C. and Tyson, P.D. 2001. Rapid climate shifts in the southern African interior throughout the mid to late Holocene. Geophysical Research Letters 28: 4507-4510.

Molg, T., Hardy, D.R. and Kaser, G. 2003b. Solar-radiation-maintained glacier recession on Kilimanjaro drawn from combined ice-radiation geometry modeling. Journal of Geophysical Research 108: 10.1029/2003JD003546.

Nicholson, S.E. 2001. Climatic and environmental change in Africa during the last two centuries. Climate Research 17: 123-144.

Nicholson, S.E. and Yin, X. 2001. Rainfall conditions in Equatorial East Africa during the nineteenth century as inferred from the record of Lake Victoria. Climatic Change 48: 387-398.

Russell, J.M. and Johnson, T.C. 2005. A high-resolution geochemical record from Lake Edward, Uganda Congo and the timing and causes of tropical African drought during the late Holocene. Quaternary Science Reviews 24: 1375-1389.

Verschuren, D., Laird, K.R. and Cumming, B.F. 2000. Rainfall and drought in equatorial east Africa during the past 1,100 years. Nature 403: 410-414.

Wagnon, P., Ribstein, P., Francou, B. and Sicart, J.E. 2001. Anomalous heat and mass budget of Glaciar Zongo, Bolivia, during the 1997/98 El Niño year. Journal of Glaciology 47: 21-28.

Related Links

Effects of climate change in Asia

Effects of climate change in Europe

Effects of climate change in North America

Effects of climate change in South America

Effects of climate change at the Poles

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