Climate Change 2001 Assessment

4. What are the likely consequences of climate change?

• 4.1 Has climate change already started to affect us?
• 4.2 How potentially could climate change affect us?
• 4.3 What other major impacts could climate change possibly have?
• 4.4 What should be done?

4.1 Has climate change already started to affect us?

4.1.1 Regional changes in climate, particularly increases in temperature, have already affected a diverse set of physical and biological systems in many parts of the world.

Examples include: shrinkage of glaciers, thawing of permafrost, later freezing and earlier break-up of ice on rivers and lakes, lengthening of mid- to high-latitude growing seasons, poleward and altitudinal shifts of plant and animal ranges, declines of some plant and animal populations, and earlier flowering of trees, emergence of insects and egg-laying in birds.

Regarding human systems, there are preliminary indications that some social and economic systems may have been affected by the recent increasing frequency of floods and droughts in some areas. More...

4.2 How potentially could climate change affect us?

4.2.1 Natural systems can be especially vulnerable to climate change because of limited adaptive capacity. While some species may benefit from climate change, existing risks of extinction could increase for some more vulnerable species. The risk of damage will increase with the magnitude and rate of climate change. More...

4.2.2 Human systems that are sensitive to climate change include mainly water resources; agriculture (especially food security) and forestry; coastal zones and marine systems (fisheries); human settlements, energy, and industry; insurance and other financial services; and human health. Vulnerability varies with geographic location, time, and social, economic, and environmental conditions. Some effects will be adverse but some others beneficial. More...

4.3 What other major impacts could climate change possibly have?

Some extreme events such as droughts, floods, heat waves, avalanches, and windstorms are projected to increase in frequency and/or severity, others such as cold spells are projected to decrease. The damage, hardship, and death caused is also expected to increase with global warming (see Figure SPM-2). The impacts are expected to fall disproportionately on the poorer regions.

There is a potential for large-scale and possibly irreversible impacts but this risk has yet to be reliably quantified. Examples include:
- slowing of the warm North Atlantic currents,
- large reductions in the Greenland and West Antarctic Ice Sheets and
- accelerated global warming due to releases of terrestrial carbon from permafrost regions and methane from hydrates in coastal sediments.
The likelihood of many of these changes is probably very low but is expected to increase with the rate, magnitude, and duration of climate change. More...

See Table SPM-1: Examples of impacts resulting from projected changes in extreme climate events.

4.4 What should be done?

Adaptation could reduce adverse impacts of climate change and enhance beneficial impacts, but will incur costs and will not prevent all damages. It is necessary to complement mitigation efforts with adaptation.

Based on a few published estimates, global warming of up to a few degrees C would produce:

• Net economic losses in many developing countries (low confidence⁶); the higher the warming the greater the losses (medium confidence⁶).
• A mixture of economic gains and losses (low confidence⁶) in developed countries, and losses for larger temperature increases (medium confidence⁶).
• Decreases in world gross domestic product (GDP) of a few percent (low confidence⁶), and increasing net losses for larger increases in temperature (medium confidence⁶) (see Figure SPM-2).

Policies that lessen pressures on resources, improve management of environmental risks, and increase the welfare of the poorest could simultaneously advance sustainable development and equity, enhance adaptive capacity, and reduce vulnerability to climate and other stresses. More...