Climate Change 2007 Update

5. What impacts are expected in the future?

• 5.1 What impacts are expected on natural systems?
• 5.2 What impacts are expected on human populations?
• 5.3 What impacts are expected in specific regions?
• 5.4 What is the magnitude of expected impacts?
• 5.5 What are the projected impacts of extreme climate events?

5.1 What impacts are expected on natural systems?

Over the course of the 21^st Century, many impacts are projected in a range of natural systems if no actions are taken to mitigate climate change.

5.1.1 Water availability and average river flow are projected to increase at high latitudes and in some wet tropical areas, and decrease in some dry regions at mid-latitudes and in the dry tropics. It is likely that larger and more numerous areas will be affected by droughts, while more frequent heavy precipitation events will increase flood risk. The amount of water stored in glaciers and snow cover is expected to decline, reducing water availability in regions where one-sixth of the world population currently lives. More...

5.1.2 The capacity of many ecosystems to adapt to change is likely to be exceeded this century if climate change and ongoing land use changes are unmitigated. With significant global warming (exceeding 1.5-2.5°C), 20 to 30% of plant and animal species assessed so far are likely to be at higher risk of extinction and major changes in ecosystems are expected, which would affect not only biodiversity, but also the supply of water and food. More...

5.2 What impacts are expected on human populations?

5.2.1 Globally, the potential for food production could increase if local average temperatures rise by 1 to 3°C, but would decrease if temperatures rise further. In response to a modest warming, agricultural methods in low and mid- to high latitude could be adapted to maintain cereal yields. Without adaptation, crop productivity is projected to decrease at lower latitudes for even small local warming, which would increase risk of hunger. For fisheries and aquaculture, a continued warming is projected to have adverse effects. Commercial timber productivity is globally expected to rise modestly in the short- to medium-term, with large regional variability. More...

5.2.2 Coasts will be exposed to increasing risks, such as coastal erosion, due to climate change and sea-level rise. Coastal ecosystems such as coral reefs, wetlands, and mangroves will be negatively affected. Many millions more people are projected to be flooded each year, particularly in densely-populated low-lying areas. Adaptation in coastal regions will be more challenging for developing countries. More...

5.2.3 For industries, settlements and societies, the net effects of climate change is expected to be more negative the larger the change in climate. Poor communities can be especially vulnerable, particularly those concentrated in high-risk areas such as low-lying coastal areas. The economic and social costs of extreme weather events will increase substantially in areas where they become more intense or more frequent. More...

5.2.4 The consequences of climate change are likely to affect the health of millions of people, particularly those who have a lower capacity to adapt. Impacts include:

• increases in malnutrition;
• increased disease, injury, and deaths due to heat waves, floods, storms, fires, and droughts;
• increased burden of diarrhoeal disease;
• increased frequency of problems due to higher concentrations of ground level ozone related to climate change; and,
• altered spatial distribution of some infectious disease vectors.

Climate change is expected to have some mixed effects, such as the decrease or increase of the range and transmission potential of malaria in Africa. In some areas, there might be some positive effects, such as fewer deaths from cold exposure in temperate areas, but overall the negative effects will be larger. More...

5.3 What impacts are expected in specific regions?

More specific information is now available across the regions of the world concerning the nature of future impacts in the coming decades if climate change is unmitigated. More...

5.3.1 Africa is particularly vulnerable to climate change because of the existing pressures on its ecosystems and its low capacity to adapt. By 2020, between 75 and 250 million people are projected to be affected by increasing water shortages. Agricultural production and fisheries resources are expected to decrease, reducing local food supplies and exacerbating malnutrition. More...

5.3.2 In Asia, climate change is projected to increase pressures on natural resources and the environment and thus hamper sustainable development. Glacier melt in the Himalayas is projected to increase flooding and rock avalanches, and affect water resources within the next two to three decades. It is expected that less fresh water will be available due to both climate change and population growth. Heavily populated coastal areas will be at greatest risk due to increased flooding. Crop yields could increase in East and Southeast Asia while they could decrease in Central and South Asia by the mid-21^st century. The projected increase in floods and droughts is expected to increase the associated health problems and deaths due to diarrhoea. More...

5.3.3 In Australia and New Zealand a significant loss of biodiversity is projected to occur in some ecologically-rich sites, such as the Great Barrier Reef. Water security problems are projected to intensify and production from agriculture and forestry is expected to decline due to increased drought and fire. Ongoing coastal development and population growth are projected to exacerbate the risks resulting from sea-level rise and increases in the severity and frequency of storms and coastal flooding by 2050. The region has a substantial capacity to adapt because of its well-developed economy and scientific and technical capability, but natural systems can only adapt so far. More...

5.3.4 In Europe, wide ranging impacts of changes in current climate have been documented: retreating glaciers, longer growing seasons, shifts in the geographic spread of species, and health impacts due to an unprecedented heat wave. It is anticipated that nearly all European regions will be negatively affected, amplifying regional differences in natural resources and assets, with consequences for many economic sectors. Health risks due to heat waves are projected to increase in Southern, Central and Eastern Europe. Negative impacts will also include increased risk of inland and coastal floods and extensive species losses in mountain areas. In Northern Europe, climate change is initially projected to bring some benefits such as reduced demand for heating. But, as climate change continues, its negative impacts are likely to outweigh its benefits. More...

5.3.5 In Latin America, warming and associated drier soils are projected to lead to a gradual replacement of tropical forest by savanna, and to salinization and desertification of agricultural lands. There is a risk of significant species extinction in many tropical areas. Changes in precipitation patterns and the disappearance of glaciers are projected to significantly affect water availability for human consumption, agriculture and energy generation. Some countries have made efforts to adapt, through ecosystem conservation, use of early warning systems, etc. However, the effectiveness of these efforts is outweighed by technological, financial, political and social constraints. More...

5.3.6 In North America, warming in western mountains is projected to cause more winter flooding and reduce summer flows. Moderate climate change in the coming decades is projected to increase overall yields by 5-20% on agricultural lands that rely of rainfall, although major challenges are projected for crops that are near the warm end of their suitable range. Pests, diseases, and fires are expected to have increasing impacts on forests. Cities that currently suffer from heat waves are expected to see them increase in number, intensity and duration. The growth of populations in coastal areas increases vulnerability to tropical storms which could become more intense. More...

5.3.7 In the Polar Regions, the main effect foreseen is a reduction in thickness and extent of glaciers, ice sheets, sea ice, and permafrost, and associated impacts on infrastructures, ecosystems, and traditional ways of life. Beneficial impacts would include reduced heating costs and more navigable northern sea routes. Arctic human communities are already adapting to climate change, but their capacity to adapt is limited. More...

5.3.8 Small Islands are especially vulnerable to the effects of climate change, sea level rise and extreme events. They are at risk of coastal erosion, floods, storm surges, which could harm tourism and affect the livelihood of local communities. Climate change could also cause reduce water resources and increase the risk of invasion by non-native species. More...

5.4 What is the magnitude of expected impacts?

Thanks to recent data, the magnitude of impacts can now be better estimated for possible increases in global average temperature. Impacts are expected to increase with temperature, as indicated in Figure SPM-2.For instance:

• Some crops will have better productivity if temperatures increase by 1 to 2°C, but if temperatures rise by 3-4°C, those same crops will be negatively affected.
• Coral reefs are already affected by small global temperature increase. They would further suffer if temperatures increased by 1 to 2°C, and many would die if it increased by 2.5°C.

If warm temperatures persist after the 21^st century, it could result in very large impacts. For instance, the large sea-level rise (up to 12 m) that would result from the melting of the Greenland and Antarctic ice sheets would have major impacts on coastal areas, with effects both on biological systems and human populations.

It is very unlikely that the North Atlantic Ocean circulation that gives rise to the Gulf Stream will undergo a large abrupt transition during the 21^st century. A slowing of this circulation is very likely over this century, but temperatures over the Atlantic and Europe are projected to increase nevertheless, due to global warming.

Global mean losses could be 1-5% of the world Gross Domestic Product (GDP) for 4°C of warming, with larger percentage losses in developing countries (Note: 1% represented US$ 650 billion in 2006).

Many estimates of net costs of damages from climate change across the globe are now available. The average estimate for 2005 was US$12 per tonne of carbon dioxide with a large variability between estimates. Such global cost estimates tend to mask significant differences across sectors, regions, countries, and populations. In some locations and amongst some groups net costs will be significantly larger.

Overall, the published evidence indicates that the net cost of climate change is likely to be significant and to increase as global temperatures increase. More...

5.5 What are the projected impacts of extreme climate events?

An increase in the severity and frequency of extreme weather events is projected to have major impacts over the course of the 21^st century (See Table SPM-1). For instance:

• An increase in the frequency and intensity of heat waves would decrease agriculture production in affected areas, cause water availability problems and increase the number of heat-related deaths.
• In colder regions, an increase in temperature would lead to fewer cold nights and more frequent warm days, which in turn would lead, to increased agricultural productivity, fewer deaths from cold exposure, and reduced energy demand for heating.
• An increase in heavy precipitation events would lead to increased floods, to soil erosion, and to negative impacts on surface and groundwater quality.

More...