Climate Change 2001 Assessment

3. What climate changes are expected for the future?

• 3.1 What emission scenarios are projected?
• 3.2 What climate changes are projected for the 21^st century?
• 3.3 What climate changes are projected for future centuries?

3.1 What emission scenarios are projected?

Human influences will continue to change atmospheric composition throughout the 21^st century.

Several emission scenarios were developed by the IPCC, using various hypotheses for the developments in population, technology, income, regional wealth differences... (see the summary for 6 of them). These scenarios were fed into computer models to make projections of atmospheric concentrations of greenhouse gases and aerosols, and hence of future climate changes (see Figure 5). More...

3.2 What climate changes are projected for the 21^st century?

Global average temperature and sea level are projected to rise under all IPCC scenarios during the 21^st century.

The global climate of the 21^st Century

• The average global surface temperature is projected to increase by something between 1.4 and 5.8°C (2.5 to 10°F) over the period 1990 to 2100. This wide range is equally due:
  • to the level of greenhouse gases emissions supposed by each scenario
  • to the response of the individual computer model used (see Figure 5d)
• The projected rate of warming is very likely⁷ to be the fastest in at least the last 10,000 years.
• It is very likely⁷ that nearly all land areas will warm more rapidly than the global average, particularly those at high northern latitudes in the cold season (see map).
• Precipitation is projected to increase, with larger year to year variations, especially in mid- to high northern latitudes and Antarctica in winter (see map).
• Some extreme events are expected to increase in severity (see Table 1). For some others, there is not enough information to make confident projections.
• Most models show weakening of the ocean thermohaline circulation. This would reduce the temperature increase in high latitudes of the Northern Hemisphere.
• Northern Hemisphere snow cover and sea-ice extent are projected to decrease further, as well as glaciers and ice caps. The Antarctic ice sheet is likely⁷ to gain mass while the Greenland ice sheet is likely⁷ to lose mass. It is very unlikely⁷ that there will be a loss of grounded West Antarctic ice raising substantial the sea level.
• Sea level is projected to rise by something between 9 and 88 cm (3.5 to 35") between 1990 and 2100, due primarily to thermal expansion and loss of ice. This wide range is due mostly to model uncertainties (see Figure 5e).

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3.3 What climate changes are projected for future centuries?

Anthropogenic climate change will persist for many centuries.

• Emissions of long-lived greenhouse gases (i.e., CO₂, N₂O, PFCs, SF₆) have a lasting effect on atmospheric composition and climate. Even after greenhouse gas concentrations have stabilized, global average surface temperatures would continue rising at a reduced rate.
• Global mean surface temperature increases and rising sea level from thermal expansion of the ocean are projected to continue for hundreds of years after stabilization of greenhouse gas concentrations (even at present levels).
• Ice sheets will continue to react to climate warming and contribute to sea level rise for thousands of years after the climate has stabilized. For instance, a Greenland warming of 5.5°C, if sustained for 1,000 years, would likely⁷ result in a sea level rise of about 3 meters.

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