IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability Summary of agriculture and forestry

Trends in individual climate variables or their combination into agro-climatic indicators show that there is an advance in phenology in large parts of North America and Europe, which has been attributed to recent regional warming. In temperate regions, there are clear signals of reduced risk of frost, longer growing season duration, increased biomass, higher quality (for grapevines, a climate-sensitive crop), insect expansion, and increased forest-fire occurrence that are in agreement with regional warming. These effects are hard to detect in aggregate agricultural statistics because of the influence of non-climate factors, particularly where advances in technology confound responses to warming. Although the present effects are of limited economic consequence and appear to lie within the ability of the sectors to adapt, both agriculture and forestry show vulnerability to recent extreme heat and drought events.

1.3.7 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 Study 
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  
High latitudinal spread of ticks – vectors for Lyme disease – with milder winters in Sweden and the Czech Republic Lindgren et al., 2000; Danielová et al., 2006 
Food- and water-borne diseases Salmonellosis in Australia associated with higher temperatures E. coli and Cryptosporium outbreaks could not be attributed to climate change  D’Souza et al., 2004 Charron et al., 2004 
Pollen- and dust-related diseases Increasing pollen abundance and allergenicity have been associated with warming climate Pollen abundance also influenced by land-use changes Levetin, 2001; Beggs, 2004