 |
|
|
|
|
|
|
|
|
|
|
| q |
Since the
late 1970s, satellite instruments have observed small
|
|
|
oscillations
due to the 11-year solar cycle. Mechanisms for the
|
|
|
|
amplification
of solar effects on climate have been proposed,
|
|
|
but
currently lack a rigorous theoretical or observational basis.
|
|
|
| q |
Stratospheric
aerosols from explosive volcanic eruptions lead to
|
|
negative
forcing, which lasts a few
years. Several major
|
|
|
|
eruptions
occurred in the periods 1880 to 1920 and 1960 to
|
|
|
1991.
|
|
|
| q |
The
combined change in radiative forcing of the two major
|
|
|
natural
factors (solar variation and volcanic aerosols) is
|
|
|
|
estimated
to be negative for the past two, and possibly the past
|
|
|
four,
decades.
|
|