Climate Change 2001:
Working Group I: The Scientific Basis
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Figure 4.1: (a) Change in CH4 abundance (mole fraction, in ppb = 10-9) determined from ice cores, firn, and whole air samples plotted for the last 1,000 years. Data sets are as follows: Grip, Blunier et al. (1995) and Chappellaz et al. (1997); Eurocore, Blunier et al. (1993); D47, Chappellaz et al. (1997); Siple, Stauffer et al. (1985); Global (inferred from Antarctic and Greenland ice cores, firn air, and modern measurements), Etheridge et al. (1998) and Dlugokencky et al. (1998). Radiative forcing, approximated by a linear scale since the pre-industrial era, is plotted on the right axis.
(b) Globally averaged CH4 (monthly varying) and deseasonalised CH4 (smooth line) abundance plotted for 1983 to 1999 (Dlugokencky et al., 1998). (c) Instantaneous annual growth rate (ppb/yr) in global atmospheric CH4 abundance from 1983 through 1999 calculated as the derivative of the deseasonalised trend curve above (Dlugokencky et al., 1998). Uncertainties (dotted lines) are ±1 standard deviation. (d) Comparison of Greenland (GRIP) and Antarctic (D47 and Byrd) CH4 abundances for the past 11.5 kyr (Chappellaz et al., 1997). The shaded area is the pole-to-pole difference where Antarctic data exist. (e) Atmospheric CH4 abundances (black triangles) and temperature anomalies with respect to mean recent temperature (grey diamonds) determined for the past 420 kyr from an ice core drilled at Vostok Station in East Antarctica (Petit et al., 1999).

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