Climate Change: What's Going On With the Sun?
SETI Institute: 189 Bernardo Avenue #100, Mountain ViewWatch online:
https://plus.google.com/events/csqif06cn5u5auhv7bbsigr471o
Dan Lubin
SETI Institute
Throughout
the past century, while greenhouse gas (GHG) abundances have been
steadily increasing and influencing Earth’s climate, the Sun has
remained relatively bright and quiescent. Solar cycles have been
steadily active, with instantaneous sunspot numbers at solar maximum
exceeding 100 in every cycle since 1893 (Cycle 13). The climate warming
we have experienced since the beginning of the modern industrial era
cannot be attributed to the Sun. However, the recent minimum between
Cycles 23 and 24, and NASA predictions of a substantially lower sunspot
number at the 2013 solar maximum, suggest that the Sun’s recent bright
and quiescent period may be ending. Both autocorrelation studies of
recent solar cycles, and studies of solar analogs in nearby field stars,
suggest a >40% chance of the Sun entering a new Maunder Minimum
sometime in the Twenty First Century. During the historical Maunder
Minimum (1645-1715), meteorological data from Europe and proxy records
from global oceans indicate a substantially cooler climate, attributable
to decreased solar irradiance. In our lifetime, we may therefore see a
period of solar dimming in conjunction with increasing GHG abundances. A
new Maunder Minimum would not entirely offset the projected GHG-induced
warming (the GHG radiative forcing is at least three times larger than
best estimates of the solar irradiance decrease). Instead, the complex
interactions between radiative balance and atmospheric dynamics yield
unusual regional patterns of pronounced warming versus cooling. This
seminar will address the physical basis of climate change in the context
of both GHG and solar variability, and will also extend the discussion
to the influence of stellar variability upon habitable zones.
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