Anonymous writes: http://www.hno.harvard.edu/gazette/1997/11.06/BrighteningSuni.html
Brightening Sun is Warming Earth May account for major part of global warming
By William J. Cromie
There is a better explanation for global warming than air pollution, two Harvard researchers say: the Sun is increasing in brightness and radiance.
"Changes in the Sun can account for major climate changes on Earth for the past 300 years, including part of the recent surge of global warming," claims Sallie Baliunas, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CfA).
"We're not saying that variations in solar
activity account for all of the global rise in temperature that we are
experiencing," cautions her CfA colleague, astrophysicist Willie Soon.
"But we believe these variations are the major driving force.
Heat-trapping gases emitted by smokestacks and vehicles -- the
so-called greenhouse effect -- appear to be secondary."
that conclusion proves true, it promises a huge economic and political
impact on the "third rock from the Sun." The Clinton Administration is
trying to negotiate an international treaty to gradually reduce
greenhouse pollutants without bringing economic havoc to industries
that satisfy our enormous appetite for the energy that comes from
burning oil, coal, and gas.
leaders and environmentalists are pushing for immediate action, but
Baliunas thinks there is time to carefully consider what action to
take. "The best models of global warming call for a very slow
temperature rise of less than two degrees in the next 100 years," she
has told various congressional committees and briefings. "There is time
for more research and a measured response because the penalty you pay
in increased temperatures from greenhouse warming is small."
that's cost-effective to cut emissions can be done right away, Baliunas
says. Dramatic cuts with high economic penalties might be postponed in
the expectation that more effective and affordable technologies will
become available in the next 25 years or so.
ease the economic burdens, President Clinton has proposed various
incentives. These include offering $5 billion in tax breaks for
businesses to conserve energy and to develop new technologies, such as
efficient electric cars and fuel cells that burn clean hydrogen. Vice
President Al Gore described these incentives last Friday in a talk at
the Kennedy School of Government.
A Bright Connection
and Soon base their ideas about the cause of global warming on
irrefutable evidence that sunlight is getting stronger. Since the late
1970s, three Sun-watching satellites recorded surprising changes in
heat, ultraviolet radiation, and solar wind. The radiation alters the
paths of winter storms; solar winds affect cloudiness and rainfall.
increased activity, everyone agrees, is tied to a cycle that sees the
Sun dimming, then brightening, every 11 years or so. From the late
1970s to mid-1980s, activity on Earth's star declined. Since then it
has risen, declined, then risen again. The satellites measured an
increase in brightness of as much as 0.14 percent on the latest rise.
unknowns, however, prevent Sun-watchers from making any useable
forecasts about the next five years. No one knows why the Sun cycles
like it does, or when it will reach its next maximum. The best guess is
the year 2000.
Also, a 0.14 percent
jump in brightness is not enough to account for the approximately 1
degree F rise in temperature on Earth in the past 100 years. What's
more, various observations show that our planet is almost 2 degrees F
warmer than it was around the year 1700.
quickly points out that the satellite measurements apply to only one
cycle, and evidence exists that the estimated jump in brightness over
several previous cycles was almost four times as much -- 0.5 percent.
looking elsewhere in the Milky Way reveals larger shifts in brightness
of other Sunlike stars. Twenty years ago, when still a Harvard graduate
student, Baliunas took over a project that has been recording
brightness changes in such stars of between 0.1 and 0.7 percent.
change of 0.5 percent in brightness sustained over several past cycles
could account for the 2 degree change in climate we have experienced
since the beginning of the 18th century," Baliunas maintains. "We don't
know if this actually happened, but it indicates that the Sun is a
major driver of climate change. We cannot ignore its variations when
accounting for the present global warming."
Sun Spots and Storms
is more, these Baliunas-Soon assumptions consider only brightness
changes. Also increasing during the maximum part of solar cycles are
invisible but potent ultraviolet rays which heat up Earth's atmosphere
and change the paths of winter storms.
radiation hits oxygen molecules in the upper stratosphere and converts
them to ozone. Some 25 miles above our heads, the ozone layer is best
known for screening out ultraviolet radiation implicated in skin
cancer, cataracts, and crop damage. However, researchers at Harvard's
Department of Earth and Planetary Sciences have found that increased
amounts of ozone interfere with movement of heat from the equator to
the poles. That, in turn, shifts the pattern of jet streams that steer
the storms around the planet.
how this contributes to warming Earth during maximum solar activity,
and to cooling it during minimums, remains a mystery. "Our uncertainty
is enormous," Soon admits, "but we can't omit ultraviolet forcing as a
factor in global warming."
striking markers of the Sun's waxings and wanings are the coming and
going of black spots on its face. Sunspots mark areas where strong
magnetic fields exit and enter the surface of the Sun. They are about a
thousand degrees cooler than the bright areas that surround them, but
are still incandescently hot.
spots not only follow an 11-year cycle; they also cycle through longer
periods of high and low magnetic activity. When the Sun boasts a
maximum of spots, cycle after cycle, Earth tends to be warmer than when
its face is clear.
During the years
from 1640 to 1720, for example, observers counted abnormally few
sunspots and Earth's climate entered a period of unusually cold
weather. Since the mid-1960s, solar magnetism has been increasing along
with global temperatures.
maximums, the wind of magnetic fields and charged particles that
normally wafts across the 93 million miles from Sun to Earth blows
harder. These gusts can trigger colorful displays of auroral lights
during long polar nights. The strongest winds may also disrupt
long-range radio communications, cause power outages, and disturb the
operation of satellites.
also produce radioactive carbon atoms in the atmosphere that eventually
rain down and become assimilated into tree rings. High solar winds lead
to rings with fewer radioactive atoms and vice versa. Changing levels
of radiocarbon provide a natural record of magnetic changes on the Sun
that can be matched with weather records of coldings and warmings.
have been 19 cold periods in the past 10,000 years and a decrease in
solar magnetic activity can be linked to 17 of them," Baliunas notes.
how this happens remains unknown. It probably involves both changes in
energy and variations in electrical charges on drops of water in the
atmosphere. The drops provide seeds for the formation of clouds which
add to natural and greenhouse warmings.
Baliunas nor Soon ties these changes to El Niño, the periodic warming
of the tropical Pacific Ocean that brings mostly unwanted weather
changes from India to Indiana. "There is no solar cycle with the same
4-to-7-year period and no known direct connection with changes on the
Sun," Baliunas says.
periods, both the ultraviolet radiation and the particles in solar
winds alter the balance of energy in the atmosphere, affecting the
movement of winds," Soon points out. "Together with changes in
brightness, these mechanisms must affect longer-term changes in
climate. All the records we have of climate tie it to variations in the
Sun. It is reasonable to assume that that effect persists at the
No one doubts this; but
the magnitude of its influence on global warming remains in question.
However, a significant number of researchers insist that solar changes
are not great enough to produce the warming we are experiencing. They
maintain that human activity is the main cause of rising temperatures
that threaten widespread flooding, increased storminess, and
potentially disruptive shifts in croplands. It is this group that wants
to take immediate action to reduce heat-trapping air pollutants.
and Soon maintain that interest in and understanding of solar effects
will increase faster than rising temperatures, allowing time to study
the Sun-climate relationships.
Baliunas admits, "I am addressing scientific issues. Economic,
political, and environmental considerations are quite another story."
Copyright 1998 President and Fellows of Harvard College