Climate change will have a significant effect on disease, and one of the most deadly diseases that will be substantially affected by a warming trend is malaria. Malaria is one of the most deadly diseases in the world, and is attributable to about 655,000 deaths every year, 90% of which occur in sub-Saharan Africa. Malaria is responsible for a 1.3% growth penalty per year in some African countries, which means that malaria hinders the economic growth of countries affected by it. This disease costs Africa more than $12 billion in lost GDP each year. In addition, malaria kills 10,000 pregnant women and 200,000 infants in Africa each year, and is the cause of 1 in 5 childhood deaths around the world. However, malaria is not limited to Africa. Roughly half of the world’s population, or 3.3 billion people, are at risk of malaria. Most scientists believe that this number will rise with climate change.
Credit: The Earth Institute, Columbia University: http://www.earth.columbia.edu/articles/view/41
Malaria flourishes in warm, humid environments, and as the climate warms, most scientists believe that many areas may experience these climate conditions that are favorable to the protozoan that causes malaria, called genus Plasmodium. This is spread through the vector, or carrier mosquitoes. The climate has direct effects on malaria because the climate influences the behaviors and geographical distribution of the mosquitoes as well as their life cycles. An increase in temperature would allow the spread of both the vector and the agent to higher latitudes and altitudes, because the mosquitoes would be able to survive in the future conditions of areas that were formerly not climatically favorable to malaria. In other words, an increase in the global climate would create more places with conditions where mosquitoes can thrive.
It has been hypothesized that an increase in the global temperature of three degrees Celsius by 2100 could increase the number of malaria cases by 50-80 million. An increase in temperature would also affect areas where malaria is already established by reducing the interval between the mosquito’s blood meals and shortening the incubation period of the parasite in the mosquito. In addition, warming trends during cold periods may make the transmission of malaria less seasonal, which would increase the overall incidence of the disease.
Credit: Hugo Ahlenius, UNEP/GRID-Arendal: http://www.grida.no/graphicslib/detail/climate-change-and-malaria-scenario-for-2050_bffe
Besides malaria, a changing climate can affect many other diseases. Many of the major diseases, such as diarrheal diseases, malnutrition, and dengue are highly climate sensitive and are expected to worsen as the climate changes. Extreme weather events caused by global warming are becoming more frequent, and scientists have attributed 140,000 excess deaths annually to this warming from the 1970’s to 2004. In addition, extreme heat is a major contributor to deaths from cardiovascular and respiratory disease, particularly among the elderly. The higher temperatures caused by global warming also raise the levels of ozone and other pollutants in the air, which increases urban air pollution and can exacerbate cardiovascular and respiratory disease. Allergens, especially to pollen and ragweed, are very climate-sensitive, and are higher in extreme heat.
Climate change also has the possibility to affect rainfall patterns, and this is likely to affect the supply of fresh water. A lack of fresh water can compromise hygiene and increase the risk of diarrheal diseases and other diseases from contaminants in the water. In extreme cases, water scarcity can lead to drought and famine.
"Understanding Malaria," a scientific data visualization: http://arcadenw.org/article/scientific-visualization