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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 (pCO2) 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
(pCO2 increase to 700 ppm by 2100). Bars to the right indicate
the predictions for 2091–2100 for the scenarios B1 (blue bar, pCO2
increases to 500 ppm by 2100), A1B (orange bar, pCO2 increases to
700 ppm by 2100), and A2 (red bar, pCO2 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.