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Background Information > Fact Sheets

The Consequences for the Future

Many natural systems, on all continents and in some oceans, are being affected by regional climate changes, particularly temperature increases.

"Climate Change 2007"
Intergovernmental Panel on Climate Change

Higher Temperatures, More Risk

• In all regions of the world, the faster temperatures rise, the greater the risk of damage. The climate does not respond immediately to emissions, which can last for years or decades in the atmosphere. And because of the delaying effect of the oceans — which absorb and eventually release heat more slowly than the atmosphere — surface temperatures do not immediately respond to greenhouse gas emissions. As a result, climate change will continue for hundreds of years after atmospheric concentrations have stabilized.

Adverse Changes in the Hydrological Cycle

• Rising temperatures are already accelerating the hydrological cycle. A warmer atmosphere holds more moisture, becomes less stable and produces more precipitation, particularly in the form of heavy rain bursts. Greater heat also speeds up evaporation. The net effect of these changes in the cycling of water will be a decline in the quantity and quality of freshwater supplies in all major regions. Meanwhile, wind patterns and storm tracks are likely to change. The intensity (but not the frequency) of tropical cyclones are expected to increase, with larger peak wind speeds and heavier rains.

Increased Health Risks

• Climate change will increasingly alter the distribution of malarial mosquitoes and other carriers of infectious diseases, affect the seasonal distribution of some allergy-causing pollen and increase the risks of heat waves. On the other hand there should be fewer deaths due to the cold.

Threats to Biodiversity

• Wildlife and biological diversity — already threatened by habitat destruction and other human-generated stresses — will face new challenges from climate change. Many ecosystems are already responding to higher temperatures by advancing towards the poles and up mountainsides. Some species will not survive the transition, and 20-30 per cent of species are likely to face an increased risk of extinction. The most vulnerable ecosystems include coral reefs, boreal (sub-arctic) forests, mountain habitats and those dependent on a Mediterranean climate.

Rising Sea Level

• The best estimate for how much further the sea level will rise due to ocean expansion and glacier melt by the end of the 21^st century (compared to 1989-1999 levels) is 28-58 cm. This will worsen coastal flooding and erosion.
• Larger sea-level increases of up to 1 metre by 2100 cannot be ruled out if ice sheets continue to melt as temperature rises. There is now evidence that the Antarctic and Greenland ice sheets are indeed slowly losing mass and contributing to sea level rise. About 125,000 years ago, when the polar regions were significantly warmer for an extended period than at present, melting polar ice caused the sea level to rise by 4 to 6 metres. Sea-level rise has substantial inertia and will continue for many centuries.
• The oceans will also experience higher temperatures, which have implications for sea life. Over the past four decades, for example, North Atlantic plankton have migrated pole-ward by 10 degrees of latitude. Similarly, the acidification of the oceans as they absorb more carbon dioxide will impair the ability of corals, marine snails and other species to form their shells or skeletons.

Hitting the Most Vulnerable

• The poorest communities will be the most vulnerable to the impacts of climate change as they have fewer resources to invest in preventing and mitigating the effects of climate change. Some of the most at-risk people include subsistence farmers, indigenous peoples and coastal populations.

Regional Impacts

• It is more difficult to anticipate how climate change will evolve at the regional than at the global level. Nevertheless, enormous strides have been made in recent years, allowing scientists to conclude that:
  • Africa — Very vulnerable to climate change and climate variability due to endemic poverty, weak institutions, and complex disasters and conflicts. Drought has spread and intensified since the 1970s, and the Sahel and southern Africa have already become drier during the 20^th century. Water supplies and agricultural production will likely be severely compromised. Yields in some countries could drop by as much as 50 per cent by 2020, and some large regions of marginal agriculture are likely to be forced out of production. Forests, grasslands and other natural ecosystems are already changing, particularly in southern Africa. By the 2080s, the amount of arid and semi-arid land in Africa will likely increase by 5-8 per cent.
  • Antarctica — This continent has proven more difficult to understand and predict. With the exception of the rapidly warming Antarctic Peninsula, both temperatures and snowfall have remained relatively constant for the continent as a whole over the past 50 years. Because this frozen continent contains almost 90 per cent of the planet's freshwater, researchers are watching carefully for any signs that its glaciers and ice sheets may be melting.
  • The Arctic — Average temperatures in the Arctic have increased almost twice as fast as the global average over the past 100 years. The average extent of Arctic sea ice has been shrinking by 2.7 per cent per decade and large areas of the Arctic Ocean could lose year-round ice cover by the end of the 21^st century if human emissions reach the higher end of current estimates. The Arctic is also particularly important because changes there have important global implications. For example, as ice and snow melts, the Earth’s albedo (reflectivity) is decreased, trapping heat that would otherwise be reflected and warming the earth’s surface even further.
  • Asia — More than a billion people could be affected by a decline in the availability of freshwater, particularly in large river basins, by 2050. Glacier melt in the Himalayas, which is projected to increase flooding and rock avalanches, will affect water resources in the next two to three decades. As glaciers recede, river flows will decrease. Coastal areas, especially heavily populated mega-delta regions, will be at greatest risk due to increased flooding from the sea and, in some cases, from river flooding.
  • Australia and New Zealand — Increasing stress on water supplies and agriculture, changing natural ecosystems, less seasonal snow cover and shrinking glaciers. Over the past few decades there have been more heat waves, fewer frosts and more rain in north-west Australia and south-west New Zealand; less rain in southern and eastern Australia and north-eastern New Zealand; and an increase in the intensity of Australian droughts. The climate of the 21^st century is virtually certain to be warmer with more frequent and intense heat waves, fires, floods, landslides, droughts and storm surges.
  • Europe — Glaciers and permafrost are thawing, growing seasons are lengthening and weather extremes — such as the disastrous heat wave of 2003 — are more frequent. Researchers believe that Europe’s northern regions will experience warmer winters, greater precipitation, expanding forests and greater agricultural productivity. Southern regions near the Mediterranean will see hotter summers, less precipitation, more droughts, retreating forests and reduced agricultural productivity. Europe contains a great deal of low-lying coastland vulnerable to rises in sea-level, and many plants, reptiles, amphibians and other species are likely to become endangered by the end of the century.
  • Latin America — The tropical forests of eastern Amazonia and southern and central Mexico are expected to be gradually replaced by savannah. Parts of north-east Brazil and most of central and northern Mexico will become more arid due to a combination of climate change and human land management. By the 2050s, 50 per cent of agricultural lands are highly likely to be experiencing desertification and salinization.
  • North America — Climate change will further constrain water resources, already stretched by growing demand from agriculture, industry and cities. Rising temperatures will further diminish the mountain snow pack and increase evaporation, thus altering the seasonal availability of water. Lower water levels in the Great Lakes and major river systems will affect water quality, navigation, recreation and hydropower. Wildfire and insect outbreaks will continue to intensify in a warmer world with drier soils. Over the 21^st century, pressure for species to shift north and to higher elevations will fundamentally rearrange North American ecosystems.
  • Small island states — Particularly vulnerable to climate change, their limited size makes them more prone to natural hazards and external shocks, in particular to rises in sea-level and threats to their freshwater resources.

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