Human health

Here we evaluate evidence regarding observed changes in human health, important health exposures, and regional climate change. These observed changes are primarily related to temperature trends and changes in temperature extremes and relate to a range of infectious and non-infectious disease outcomes. These relationships are difficult to separate from the effects of major climate variability systems such as ENSO, which have been shown to be associated with the transmission and occurrence of diseases in certain locations (Kovats et al., 2003; Rodo et al., 2002). Additionally, temperature and rainfall variability can be important determinants of the transmission of vector-borne diseases (Githeko and Ndegwa, 2001).

There is little evidence about the effects of observed climate change on health for two reasons: the lack of long epidemiological or health-related data series, and the importance of non-climate drivers in determining the distribution and intensity of human disease. Studies that have quantified the effect of climate or weather on health outcomes are listed in Table 1.11. There is a wide range of driving forces that can affect and modify the impact of climate change on human health indicators. Consideration of reported trends in a given disease and the attribution to climate change needs to take into account three possible conditions.

1. That the change in disease incidence is real and due to changes in important non-climate determinants which include social factors, such as human population density and behaviour; housing facilities; public health facilities (e.g., water supply and general infrastructure, waste management and vector-control programmes); use of land for food, fuel and fibre supply; and results of adaptation measures (e.g., drug and insecticide use), as well as changed insecticide and drug resistance in pathogens and vector species (Tillman et al., 2001; Githeko and Woodward, 2003; Molyneux, 2003; Sutherst, 2004). Changes in land use and land cover can affect the local climate and ecosystems and should be considered when linking climate and health (Patz et al., 2005).

2. That the change in disease incidence is real and due to changes in climate factors, once all non-climate determinants have been considered and excluded as the main explanation (see, for example, Purse et al., 2006).

3. That the change in disease incidence is not real, but is only apparent due to changed reporting or may be due to changes in other apparent factors such as population growth or movement.

Table 1.11. Studies of the effects of weather and climate on human health.

Health effect

Climate effect on health

Other driving forces


Direct impacts of heat or cold

Temperature-related mortality in summers

Declining summer death rates due to air-conditioning adaptation

Diaz et al., 2002; Davis et al., 2003b; Beniston, 2004; Kysely, 2004

Vector-borne diseases

Tick-borne encephalitis (TBE) increases in Sweden with milder climate

Increases in TBE may be due to changes in human and animal behaviour

Randolph, 2001

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