6 What are the regional effects of climate change on different parts of the world?

This section briefly covers the main points from the UK CCC's excellent summary of the impacts and vulnerabilities in different regions of the world, based on the IPCC Fourth Assessment Report.

Areas particularly vulnerable to climate change include the Arctic (recent rapid reductions in the extent and thickness – of particular concern is the loss of ‘old’ ice), mountain ecosystems (where climate change pushes the habitable zone uphill until it runs out) and the Amazon rainforest (drought and fire).

Water. Dry regions get drier; wet regions get wetter and 1–2 billion people at risk for a 2°C warming. Longer droughts interspersed with heavier rainfall, leading to water management problems. Retreating glaciers and ice cover remove water sources for around 1 billion people. Areas particularly affected by water stress: southern Africa, the Andes, Asia, Australia, Mediterranean Europe and western USA.

Ecosystems. Climate exacerbates other human pressures on ecosystems. But 20–30% of plant and animal species face a ‘commitment to extinction’ directly as a result of climate change for a temperature rise of 2–3°C. After 4°C warming, major extinctions are likely. Systems at particular risk include tundra, mountain and Mediterranean-type systems, mangroves and coral reefs, all with significant knock-on consequences. Ocean acidification is expected to make it more difficult for marine organisms to form calcareous shells, with negative consequences across the food chain.

Food. Impacts on crop production are likely to differ markedly by region. Local warming of about 1–3°C gives positive impacts for food supply in temperate zones, depending on the crop. But in low latitudes expect falling productivity even for very low global temperature increases. Beyond a global average 3°C increase, world food production is projected to fall in all regions. Increased flooding and drought is also likely to put crops at risk. Areas facing a particular threat to food security and income include Africa, Asia and Latin America. Continued changes to the distribution of fish species are expected to have adverse impacts on fisheries.

Coasts. Large settlements and concentrations of infrastructure are often situated on coasts (e.g. eastern USA, Bangladesh and eastern China). Many small islands are also very exposed to changes in sea level. The IPCC estimated global average sea level rise of up to 59 cm above 1980–1999 levels by the end of this century, excluding the possibility of rapid melting of the Greenland and West Antarctic ice sheets. Up to 3 million people could be at risk of coastal flooding for a 2°C global temperature rise, with poor communities more exposed through their limited adaptive capacity. More recently, other studies have suggested that a global rise of 1.6 ± 0.8 m by 2100 may be more realistic.

Health. Despite some benefits, such as fewer deaths from cold exposure, climate change is likely to have a net negative impact on human health. Increases in deaths, diseases and injuries from heatwaves, floods, storms, fires and droughts are predicted, as well as problems associated with poorer air quality in urban areas. Reduction in crop productivity in low latitudes will increase levels of malnutrition. Infectious diseases will become less prevalent in some areas and more so in others.

Singular events. Rather than steadily varying impacts, major shifts in the Earth system may exceed some threshold, making them effectively irreversible. Examples include the possible melting of the Greenland and West Antarctic ice sheets. Models suggest that Greenland could start irreversible melting as a result of sustained global warming of 1.9–4.6°C.