gure SPM-2: Simulating
the Earth's temperature variations (°C) and comparing the results to
the measured changes can provide insight to the underlying causes of the major
changes. A climate model can be used to simulate the temperature changes
that occur from both natural and anthropogenic causes. The simulations represented
by the band in (a) were done with only natural forcings: solar variation and volcanic
activity. Those encompassed by the band in (b) were done with anthropogenic forcings:
greenhouse gases and an estimate of sulfate aerosols. And those encompassed by
the band in (c) were done with both natural and anthropogenic forcings included.
From (b), it can be seen that the inclusion of anthropogenic forcings provides
a plausible explanation for a substantial part of the observed temperature changes
over the past century, but the best match with observations is obtained in (c)
when both natural and anthropogenic factors are included. These results show that
the forcings included are sufficient to explain the observed changes, but do not
exclude the possibility that other forcings may also have contributed.
