Heat waves attributable in part to climate change are forecast to kill hundreds of thousands in this century, however climate change will also have disastrous effects on water supplies, agriculture, and the spread of disease. Rich and poor alike will be affected, but countries that are already struggling to provide food and water for their people will suffer the most.
Disappearing glaciers, increasing droughts and salt-water intrusion will greatly worsen our world's current fresh water shortage. The IPCC estimates 3 billion or more additional people will be at risk of water shortage due to climate change. The Stockholm Environment Institute estimates that, using only a moderate projection of climate change, 63 percent of the global population will live in countries of significant water stress by 2025.
Droughts, water shortages, rising sea levels, floods, heat waves and temperature shifts will damage food production in many parts of the world. Mid-continental areas, including vast parts of Asia and the US "grain belt," are likely to dry. In areas were dry land agriculture is dependent solely on rain, such as in sub-Saharan Africa, even a minimal increase in temperature would dramatically decrease food production.
One extremely disturbing case of how a small change can produce unexpected results is the susceptibility of rice to temperature shifts. According to a study by the International Rice Research Institute, rice yields decrease by 10 percent for every 1.8°F increase in minimum night time temperature. Rice is the staple food for more than half of the world's population - meaning this one unexpected impact of climate change could have profound consequences.
Climate change increases the spread of disease in a number of ways. Perhaps most significantly by increasing the range of tropical and sub-tropical infection bearing pests, such as malaria and dengue carrying mosquitoes. Roughly 300 million more people will be at risk of malaria with global warming of about 3.6-5.4°F. Floods will also compromise water quality - spreading cholera and other diseases.
Up in smoke? - Working Group on Climate Change and Development