Mid-latitude regions such as Europe and North America tend to have mild climates, with ranges of temperature and rainfall suitable for the growth of many cereals and other crops. A global temperature rise of 1–2 °C will lengthen growing seasons in these areas. Higher levels of carbon dioxide in the atmosphere also boost plant growth. However, increases in flood risk, heat waves and other weather extremes could disrupt food production even in temperate climate zones. Scientists predict that global warming of more than 3 °C – expected by the end of the century on current greenhouse gas emission trends – would have an overall negative impact on crop yields in all major agricultural regions.

In the tropics crop production often operates at the limits of suitability of annual temperature and rainfall, so that a combination of a 1–2 °C warming and shifts in rainfall patterns could have a disruptive effect. Maximum temperatures are predicted to rise at up to double the rate of average temperatures, potentially making heat waves far more severe. In addition, areas prone to coastal flooding, like Bangladesh, could suffer from rising sea level, with saltwater flooding damaging agricultural land. Scientists predict that global warming of 4 °C could result in a reduction of up to 40% in tropical maize and wheat yields, leaving millions more people at risk of hunger.

Marine ecosystems are sensitive to climate conditions, so will certainly respond to a changing climate. But there are many uncertainties as to the exact nature of the changes and responses, so it’s difficult to predict what the overall effects will be. If marine habitat ranges shift, some countries may be able to exploit new species that move into their waters. However, existing fishing grounds – many already threatened by overfishing – could suffer as ocean temperatures rise. Marine ecosystems are also sensitive to ocean acidification, caused by increasing carbon dioxide levels, which generally has negative impacts.

Rising average temperatures, together with more frequent extreme weather, could affect outbreaks of crop pests and diseases. The spread of some pests has already been observed. For example, evidence shows that recent warming trends in North America have caused insects to become active earlier in the spring, and the mountain pine beetle has proliferated, damaging forests. Many species of pest can also reproduce at a higher rate in warmer conditions. Scientists predict that continued temperature rises will lead to the spread of some animal diseases and pests from the tropics. Other examples include an increase in illnesses such as bluetongue – which affects sheep – in mid-latitude regions, and increasing vulnerability to cattle ticks in Australia.

• World Meteorological Organisation
• Met Office: The Developing World