From the tropics to the arctic, climate and weather have powerful direct and indirect impacts on human life. Weather extremes – such as heavy rains, floods, and disasters like Hurricane Katrina that devastated New Orleans, USA in August 2005 – endanger health as well as destroy property and livelihoods. Approximately 600 000 deaths occurred worldwide as a result of weather-related natural disasters in the 1990s, some 95% of which took place in developing countries.
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Pollen and other aeroallergen levels are also higher in extreme heat. These can trigger asthma, which affects around 300 million people. Ongoing temperature increases are expected to increase this burden.
More variable rainfall patterns are likely to compromise the supply of fresh water. Globally, water scarcity already affects four out of every 10 people. A lack of water and poor water quality can compromise hygiene and health. This increases the risk of diarrhoea, which kills approximately 2.2 million people every year, as well as trachoma (an eye infection that can lead to blindness) and other illnesses.
Over the last 50 years, human activities – particularly the burning of fossil fuels – have released sufficient quantities of carbon dioxide and other greenhouse gases to affect the global climate. The atmospheric concentration of carbon dioxide has increased by more than 30% since pre-industrial times, trapping more heat in the lower atmosphere. The resulting changes in the global climate bring a range of risks to health.
Intense short-term fluctuations in temperature can also seriously affect health – causing heat stress (hyperthermia) or extreme cold (hypothermia) – and lead to increased death rates from heart and respiratory diseases.
Rising sea levels – another outcome of global warming – increase the risk of coastal flooding, and could cause population displacement. More than half of the world’s population now lives within 60 kilometers of shorelines. Floods can directly cause injury and death, and increase risks of infection from water and vector-borne diseases.