Figure
2: Long records of past changes in atmospheric composition provide the
context for the influence of anthropogenic emissions. (a) shows changes in
the atmospheric concentrations of carbon dioxide (CO2), methane
(CH4), and nitrous oxide (N2O) over the past 1000 years.
The ice core and firn data for several sites in Antarctica and Greenland (shown
by different symbols) are supplemented with the data from direct atmospheric
samples over the past few decades (shown by the line for CO2 and
incorporated in the curve representing the global average of CH4).
The estimated positive radiative forcing of the climate system from these gases
is indicated on the right-hand scale. Since these gases have atmospheric
lifetimes of a decade or more, they are well mixed, and their concentrations
reflect emissions from sources throughout the globe. All three records show
effects of the large and increasing growth in anthropogenic emissions during the
Industrial Era. (b) illustrates the influence of industrial emissions on
atmospheric sulphate concentrations, which produce negative radiative forcing.
Shown is the time history of the concentrations of sulphate, not in the
atmosphere but in ice cores in Greenland (shown by lines; from which the
episodic effects of volcanic eruptions have been removed). Such data indicate
the local deposition of sulphate aerosols at the site, reflecting sulphur
dioxide (SO2) emissions at mid-latitudes in the Northern Hemisphere.
This record, albeit more regional than that of the globally-mixed greenhouse
gases, demonstrates the large growth in anthropogenic SO2 emissions
during the Industrial Era. The pluses denote the relevant regional estimated SO2
emissions (right-hand scale). [Based upon (a) Chapter
3, Figure 3.2b (CO2); Chapter
4, Figure 4.1a and b (CH4) and Chapter
4, Figure 4.2 (N2O) and (b) Chapter
5, Figure 5.4a]
