E. Linacre and B. Geerts
Climate change is currently indicated chiefly by warming near the surface mainly at mid and high latitudes, the rising of night-time and winter temperatures especially, and the increase of extreme weather events. There is evidence for a accelerated retreat of glaciers worldwide, and the freezing isotherm at low latitudes (less than 30 degrees) has risen by about 150 m during this century, threatening the small icefields on high mountains in the tropics. Mountain regions are particularly suited to monitoring climate change. Many 'island' ecosystems on mountain peaks may vanish as a result of the warming. Likewise, plants have been found to be growing at a higher elevation on 30 alpine peaks (1).
Climate change also has several health consequences. The changing conditions affect the distribution of insects such as mosquitoes, and there has been a resurgence and redistribution of diseases such as malaria, dengue fever, and yellow fever, which mosquitoes carry (2). Malaria is caused by a parasite that is transmitted to a person by the bite of an infected Anopheles mosquito, whereas dengue and yellow fevers are transmitted by the Aedes mosquito. Both types of mosquito thrive in warm, humid conditions. The interval between blood meals for the Anopheles mosquito is less at higher temperatures: it is 7 days on average at 15ēC, 3 days at 21ēC, and 2 days above 29ēC (3). Dengue and yellow fevers, which are limited by the wintertime 10°C isotherm, used to be found only below 1,000 m in the tropics, but now have been diagnosed above 1,500 m in central Mexico, and the Aedes mosquito has been seen at 2,200 m in Colombia. Dengue fever is relatively rare, but at this time no vaccination exists for it.
In short, global warming would increase both geographical occurrence of mosquito-borne diseases, and the infection threat in affected regions. Climate change scenarios from five different atmospheric general circulation models consistently indicate that the malaria potential occurrence zone will expand significantly, mainly in mid-latitudes, during the next few decades (4).