Figure 2-1: Records of
past changes in atmospheric composition over the last millennium demonstrate the
rapid rise in greenhouse gases and sulfate aerosols that is attributable primarily
to industrial growth since 1750. The top three panels show increasing
atmospheric concentrations of carbon dioxide (CO2), methane (CH4),
and nitrous oxide (N2O) over the past 1,000 years. Early sporadic data
taken from air trapped in ice (symbols) matches up with continuous atmospheric
observations from recent decades (solid lines). These gases are well mixed in
the atmosphere, and their concentrations reflect emissions from sources throughout
the globe. The estimated positive radiative forcing from these gases is indicated
on the righthand scale. The lowest panel shows the concentration of sulfate in
ice cores from Greenland (shown by lines for three different cores) from which
the episodic effects of volcanic eruptions have been removed. Sulfate aerosols
form from sulfur dioxide (SO2) emissions, deposit readily at the surface,
and are not well mixed in the atmosphere. Specifically, the increase in sulfate
deposited at Greenland is attributed to SO2 emissions from the U.S.
and Europe (shown as symbols), and both show a decline in recent decades. Sulfate
aerosols
