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Predicted increase in global mean surface-air temperatures

Arctic surface air-temperature change

Global surface warming, ºC

4

10 Temperature change, ºC

3

8

2

6

A2 A1B B1 Constant composition 20th century

1

4

0

2

-1

0

-2

1900

2000

2100

2200

2300 Year

-2

1900

1950

2000

2050

Year 2100

Source: IPCC2007

Figure 3.2: Predicted increase in global mean surface-air temperatures. Increases are relative to 1980–1999 for different emission scenarios (IPCC 2007). The partial pressure of carbon dioxide in the atmosphere (pCO 2 ) is assumed to attain a value of 800 to 1 000 parts per million (ppm) at the end of this century for scenario A2. It increases to about 700 ppm in scenario A1B and reaches approximately 500 ppm in scenario B1. The current pCO 2 value of about 390 ppm is maintained until the end of the century in the constant composition scenario. (See IPCC (2007) for further information.) According to the IPCC assessments, surface temperatures rose significantly over the last century, with the strongest warming signal in the Arctic (Fig. 3.1). Future trends in climate change have been estimated by the IPCC for different greenhouse gas emission scenarios (Fig. 3.2). Predictions of global surface-air-temperature increases over the next century range from 1.5 to >3 °C. As observed in the historical data, the most substantial warming is an- ticipated at high northern latitudes (Fig. 3.3) where surface

Figure 3.3: Arctic surface air-temperature change. Change is measured relative to measurements from 1901 to 1950 (black curve). Orange region is the 2001-2100 prediction given the A1B scenario (pCO 2 increase to 700 ppm by 2100). Bars to the right indicate the predictions for 2091–2100 for the scenarios B1 (blue bar, pCO 2 increases to 500 ppm by 2100), A1B (orange bar, pCO 2 increases to 700 ppm by 2100), and A2 (red bar, pCO 2 increases to 800–1 000 ppm by 2100) (IPCC 2007).

air temperatures may increase by up to 8 °C by the end of this century.

Methane release from dissociating gas hydrates is not in- cluded in the IPCC climate predictions, in part because the magnitude and timing of the induced emissions are poorly constrained and therefore difficult to forecast. Gas hydrate dissociation might nevertheless amplify future warming, ocean acidification, and oxygen loss, as discussed in Vol- ume 1, Chapter 2.

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