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FROZEN HEAT

56

Year

1900

1950

2000

2050

2100

0

2

4

6

8

10

Temperature change, ºC

-2

Arctic surface air-temperature change

-1

-2

0

1

2

3

4

1900

2000

2100

2200

2300

Global surface warming, ºC

Source: IPCC2007

Predicted increase in global mean surface-air

temperatures

A2

A1B

B1

Constant

composition

20th century

Year

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.)

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).

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

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.