165
uncertain because the measured variability of the sun seems to be generally
less that expected an anlysis of other sun-like stars (Lockwood et al., 1992).
This is of the right order of magnitude to (by itself) account for the Little
Ice Age which was coincident with the Maunder Minimum (1645 to 1715)
and involved a global cooling of order 1 degree (see Webb, 1989). (This
number is much in doubt and is inferred from 18 0 ratios taken at isolated
ice cores around the globe-see e.g. the ice core papers in Bradley and
Jones, 1992).
We may conclude, on the basis of admittedly fragmentary and indirect
evidence, that the variability in the sun's output is likely to be the cause of
decadal to centennial variability in the earth's global surface temperature
at a level of a few tenths of a degree. The ability to say more about
the effect of the future effects of the solar output on climate depends on
measuring solar radiation over long periods of time to better characterize
its characteristics and variability, on understanding the sun better so as to
better predict its output, and on better understanding the sensitivity of
the earth's climate system to small changes in solar radiation. A complete
and readable review of the effect of solar variations on the earth is given
in National Research Council (1994).
2.2 Volcanoes
It has been suggested that aerosols, both volcanic and anthropogenic, may
have a significant effect on the earth's radiation balance (e.g. Charlson and
Wigley, 1994).
Volcanic aerosols (mostly sulfate) have global impact only when significant amounts are injected into the stratosphere, where, due to lack of
effective removal mechanisms, they remain for several years. Smaller volcanic eruptions inject their aerosols into the troposphere where they are
rapidly rained out. As it turns out, the frequency of volcanic eruptions
large enough to affect the global climate is low. Pinatubo, for example,
was a once-in-a-century eruption.
The effects of the Pinatubo volcanic eruption were predicted in 1992
(Hansen et al., 1992, 1993, 1995) and later verified. The net global surface A temperature response was a spike of cooling, of amplitude 0.5°C,
which was gone in about two years. Thus the emission of the volcanic
aerosol, while having a significant effect on global climate, was a transitory
phenomenon unlikely to be the cause of major variability. It is not out
uncertain because the measured variability of the sun seems to be generally
less that expected an anlysis of other sun-like stars (Lockwood et al., 1992).
This is of the right order of magnitude to (by itself) account for the Little
Ice Age which was coincident with the Maunder Minimum (1645 to 1715)
and involved a global cooling of order 1 degree (see Webb, 1989). (This
number is much in doubt and is inferred from 18 0 ratios taken at isolated
ice cores around the globe-see e.g. the ice core papers in Bradley and
Jones, 1992).
We may conclude, on the basis of admittedly fragmentary and indirect
evidence, that the variability in the sun's output is likely to be the cause of
decadal to centennial variability in the earth's global surface temperature
at a level of a few tenths of a degree. The ability to say more about
the effect of the future effects of the solar output on climate depends on
measuring solar radiation over long periods of time to better characterize
its characteristics and variability, on understanding the sun better so as to
better predict its output, and on better understanding the sensitivity of
the earth's climate system to small changes in solar radiation. A complete
and readable review of the effect of solar variations on the earth is given
in National Research Council (1994).
2.2 Volcanoes
It has been suggested that aerosols, both volcanic and anthropogenic, may
have a significant effect on the earth's radiation balance (e.g. Charlson and
Wigley, 1994).
Volcanic aerosols (mostly sulfate) have global impact only when significant amounts are injected into the stratosphere, where, due to lack of
effective removal mechanisms, they remain for several years. Smaller volcanic eruptions inject their aerosols into the troposphere where they are
rapidly rained out. As it turns out, the frequency of volcanic eruptions
large enough to affect the global climate is low. Pinatubo, for example,
was a once-in-a-century eruption.
The effects of the Pinatubo volcanic eruption were predicted in 1992
(Hansen et al., 1992, 1993, 1995) and later verified. The net global surface A temperature response was a spike of cooling, of amplitude 0.5°C,
which was gone in about two years. Thus the emission of the volcanic
aerosol, while having a significant effect on global climate, was a transitory
phenomenon unlikely to be the cause of major variability. It is not out