Solar Fluctuations and Global Warming?

Book excerpt from Spencer Weart’s excellent The Discovery of Global Warming.

Table of Contents at the webpages of the American Institute of Physics:

Summary of chapter on the Sun’s role in setting climate on Earth:

Chapter summary: Since it is the Sun’s energy that drives the
weather system, scientists naturally wondered whether they might
connect climate changes with solar variations. Yet the Sun seemed to
be stable over the timescale of human lifetimes. Attempts to discover
cyclic variations in weather and connect them with the 11-year
sunspot cycle, or other possible solar cycles ranging up to a few
centuries long, gave results that were ambiguous at best. These
attempts got a well-deserved bad reputation. Jack Eddy overcame this
with a 1976 study that demonstrated that irregular variations in
solar surface activity, a few centuries long, were connected with
major climate shifts. The mechanism remained uncertain, but plausible
candidates emerged. The next crucial question was whether a rise in
the Sun’s activity could explain the global warming seen in the 20th
century? By the 1990s, there was a tentative answer: minor solar
variations could indeed have been partly responsible for some past
fluctuations… but future warming from the rise in greenhouse gases
would far outweigh any solar effects.

Read the whole chapter

Check out the table of contents of the whole book:


“The consensus of most scientists, arduously
hammered out in a series of international
workshops, flatly rejected the argument that the
global warming of the 1990s could be dismissed as
a mere effect of changes on the Sun. The pioneer
of historical solar influences, Jack Eddy, wrote
that if the Sun were “the only agent of climatic
change, we would live in a world where the mean
global surface temperature varied, in any
century, through limits of at most about 0.5°C.”

Similarly, in 2004 when a group of scientists
published evidence that the solar activity of the
20th century had been unusually high, they
nevertheless concluded that “even under the
extreme assumption that the Sun was responsible
for all the global warming prior to 1970, at most
30% of the strong warming since then can be of
solar origin.” When Foukal reviewed the question
in 2006, he agreed that there was no good
evidence that the Sun had played a role in any
climate change back to the Little Ice Age.
(Meanwhile, new historical evidence suggested
that the cold of the early modern centuries might
have been partly due to a spate of volcanic

“Some experts persevered in arguing that slight
solar changes (which they thought they detected
in the satellite record) had driven the
extraordinary warming since the 1970s. Most
scientists expected that these correlations would
follow the pattern of every other subtle
solar-climate correlation that anyone had
reported over the past century – fated to be
disproved by the next decade or two of data. A
few scientists persevered in studying possible
mechanisms, for example devising experiments that
they hoped would show how cosmic rays could
affect climate. Yet even if somebody did finally
manage to show an influence on climate from
changes in the Sun, it could not be very great.
Greenhouse warming was bound to swamp any solar
effects as the quantities of the gases in the
atmosphere soared ever higher. Willson, the
leader of the satellite experts, explained that
in the future,”solar forcing could be
significant, but not dominant.”(58*)”


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