The Effects of Global Warming on Droughts in Africa. By: Jacob Crawford

Transcription

1 The Effects of Global Warming on Droughts in Africa By: Jacob Crawford

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3 The thermohaline circulation is what causes what is called the North Atlantic Oscillation which regulates the surface water temperatures of the North Atlantic Ocean and the South Atlantic. When the North Atlantic is warm the South Atlantic Ocean is cool and visa versa. The thermohaline circulation works because cold, salty water up north by the arctic circle sinks due to its high density, this means warmer water from further south has to come up and take its place and this warm water is what heats up the North Atlantic. As you can see, the thermohaline circulation creates sort of a conveyor belt of hot and cold water that encompasses basically the whole globe. Due to global warming, sea ice is melting in the arctic circle, sea ice is almost entirely fresh water, and so when this fresh water enters the arctic and North Atlantic oceans it is no longer more dense than the other water around it and so it does not sink. Eventually if enough fresh water enters the oceans the thermohaline circulation will stop. In its 2007 report the IPCC says it does not think this conveyor belt will undergo any abrupt changes during this next century but it thinks it is likely it will slow down. The Sahel region of Africa experienced severe drought during the 1970 s and 1980 s as the graph shows. It appears this was linked to cool waters in the North Atlantic while the South Atlantic Ocean was warmer. Sources: Basgall, Monte. North Atlantic Warming Tied to Natural Variability; but Global Warming may be at Play Elsewhere. Duke University. 3 Jan /du naw php. Eccleston, Paul. Arctic Warming Leading to Regime Change in North Atlantic Ecosystems. Telegraph.co.uk. 11 Nov warming leading to regime change in North Atlantic ecosystems.html>. Henson, Robert. Which way will the Sahel go? The Rough Guide to Climate Change. New York: Rough Guides Ltd, , 120. Swedish Research Council. "Earth's Climate Is Seesawing, According To Climate Researchers." ScienceDaily 30 April February 2009 < /releases/2007/04/ htm>. UCAR. A Continent Split by Climate Change: New Study Projects Stronger Drought in Southern Africa, More Rain in Sahel. UCAR. 24 May IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, Source of Image: Extremes and Climate Change: Droughts. Hamburger Bildunggsserver. 27 Jul html.

4 Rainfall, or the lack there of, in the Sahel, appears to be linked to the surface temperature of the North Atlantic Ocean. When the North Atlantic has warm surface temperatures this pulls more moisture over the Sahel thus producing more rain during Monsoons. When the North Atlantic is cool the rainfall is less in the Sahel

5 Drought is when, rains stop or at least diminish for a given length of time, if a certain area is getting less rain than it normally does over an extended time period this would be a drought (Henson 68). Recently the Northern Atlantic has been getting warmer which has lead to wetter seasons in the Sahel. However, this warming trend appears to be natural. The North Atlantic Oscillation is a cyclical wind circulation pattern (Basgall 2) that strongly affects surface temperatures in the North Atlantic. At this moment the warming trend being observed there seems to be driven solely by the North Atlantic Oscillation. The North Atlantic Oscillation (NAO) is a very strong, natural event. While waters in the rest of the world appear to be warming as expected due to global warming, the North Atlantic has not been following this same trend. Global warming has surely affected water temperatures in the North Atlantic but the effects of this are not as strong as those created by the NAO. As the droughts in the Sahel of the 70 s and 80 s show the NAO created cool surface temperatures in the North Atlantic during this time and so the Sahel got less rain fall. This would not have been expected if global warming was the sole decider of North Atlantic water temperatures. Data from recent climate models show that the North Atlantic will continue to warm well into the 21 century, the warming appears to get more intense however as the century progresses which suggests slight influence from a warming climate. Sources: Basgall, Monte. North Atlantic Warming Tied to Natural Variability; but Global Warming may be at Play Elsewhere. Duke University. 3 Jan /du naw php. Eccleston, Paul. Arctic Warming Leading to Regime Change in North Atlantic Ecosystems. Telegraph.co.uk. 11 Nov warming leading to regime change in North Atlantic ecosystems.html>. Henson, Robert. Which way will the Sahel go? The Rough Guide to Climate Change. New York: Rough Guides Ltd, Swedish Research Council. "Earth's Climate Is Seesawing, According To Climate Researchers." ScienceDaily 30 April February 2009 < /releases/2007/04/ htm>. UCAR. A Continent Split by Climate Change: New Study Projects Stronger Drought in Southern Africa, More Rain in Sahel. UCAR. 24 May Source of Image: Zeng, Ning. Atmospheric Science: Drought in the Sahel. Science AAAS. 7 Nov

6 In Southern Africa, however, drought is tied to the warming of the Indian Ocean. When this ocean warms more water is pulled to that region, however this increase in water only occurs in a small area leaving the outer parts of this region to have dry, sinking air, which leads to drought. Southern Africa happens to lie on the outskirts of the wet region. (The picture is showing loss of crops in Southern Africa due to very dry conditions. Areas with green shading had no loss or had an increase in crop yield, where as the darker brown areas show places that lost a significant amount of crops)

7 During the latter half of the 20 century Southern Africa had been experiencing drought. The Indian Ocean was also getting slightly warmer during this time period. It appears this warming trend is stronger than would be expected if it was caused just by natural variations. As the planet heats up from global warming almost all of the worlds oceans have also been heating up. The Indian Ocean is no exception. It appears global warming is the culprit for the droughts Southern Africa has been experiencing. Based on recent climate models it seems these droughts will only get worse. The Indian Ocean will continue to heat up, following the trend laid out by global warming, and this will cause more severe and frequent droughts in Southern Africa. Sources: Basgall, Monte. North Atlantic Warming Tied to Natural Variability; but Global Warming may be at Play Elsewhere. Duke University. 3 Jan Eccleston, Paul. Arctic Warming Leading to Regime Change in North Atlantic Ecosystems. Telegraph.co.uk. 11 Nov Henson, Robert. Which way will the Sahel go? The Rough Guide to Climate Change. New York: Rough Guides Ltd, Swedish Research Council. "Earth's Climate Is Seesawing, According To Climate Researchers." ScienceDaily 30 April February 2009 < /releases/2007/04/ htm>. UCAR. A Continent Split by Climate Change: New Study Projects Stronger Drought in Southern Africa, More Rain in Sahel. UCAR. 24 May