Interaction between the sun and the surface waters of the world's oceans are hiking temperatures
RESEARCH on climatic shifts and patterns
acquires new dimensions every time
scientists add a new reason to the list of
factors responsible for these changes.
The latest of these proposes that the
waxing and waning of the sun - in a
regular II -year cycle - may be responsible for as many as half the increases in
global temperature. Approximately
every II years, the number of sunspots
- dark areas in the sun's photosphere - on the sun's surface increase, resulting in its dimming. The dimming of the sun
would result in the reduction of temperatures on the earth. These sunspots,
however, gradually vanish when the sun
attains maximum brightness at the end
of the 11 -year cycle. The sun now sports
a large number of faculae or bright
patches. At this point, temperatures on
the earth increase. Researchers till
now had not thought of taking the sun-
climate link too seriously (Science,
Vol 271, No 5254).
However, climatologists Daniel
Cayan and Warren White of the Scripps
Institution of Oceanography at La Jolla,
California, us, compiled data on the
Northern Hemisphere's sea surface
temperatures - valid for the last 50
years - and compared the fluctuations
in these figures with the variation in
solar irradiance, inferred from 17-year-
old satellite records. Their study ended
with the conclusion that fluctuations in
the two corresponded with each other.
The duo now approached aeronomist
Judith Lean of the Naval Research
Laboratory in WashingtonDC, US, for a
longer record on solar irradiance. Lean,
along with solar physicist Peter Foukal
of Cambridge Research and Instrumentation Inc, Massachusetts, us, came up
with a 120-year-record of the sun's II -
year sunspot cycle, and an even more
comprehensive analysis resulted. "They
(the two variables being compared) just
nailed each other and you could not tell
them apart," says a pleasantly surprised
White.
On investigation it was found that
the movement of gases on the sun
(which is after all a ball of gases), created
a magnetic field. These gases are heavier
around the centre of the sun which is
why the phenomena of waxing and
waning are more prominent around the
sun's central portion. The magnetic
field of the sun is what interacts with the
tropical and sub-tropical ocean basins
of the earth and causes fluctuations in
temperature. These climatologists have
discovered that temperatures in these
oceans - the easternmost and equatorial sections of them, to be precise -
vary by 0. I'c, every I I years. This is a
pattern similar to that observed during
the El Niho's (a periodic interaction of the equatorial section of the Pacific
Ocean and the 'atmosphere, that heats
the eastern tropical part of the ocean
and alters climates worldwide) four-to-
seven-year cycles. According to White,
similar forces may be at work in both
the cases. Significantly these variations
in temperature were found only in the
topmost layer of the oceans (the part
that was immediately exposed to the
sun's warmth), and failed to occur at
greater depths.
Although there have been isolated
and unconfirmed studies on the sun-climate relationship in the past, this is the
first time such findings have been com-
plemented by other studies conducted
by some fellow scientists. Prompted by
these recent researches, Vikrarn Mehta,
a researcher at the Goddard Space Flight
Center in Greenbelt, Maryland, us,
examined records of ocean temperatures and solar radiation. His findings
revealed a number of II -year pulses of
ocean temperatures which were in synchrony with the sunspot cycle.
Meteorologists Gerald North and
Mark Stevens of Texas A&M University,
us, also reported the presence of the II -
and 22-year (the cycle could be taken for
a 22-year-long one if the fact that the
magnetic forces of the sun take an additional I I years to revert to their original
position is taken into account) surface
temperature cycles, in the global temperature records of the past century.
However, their findings showed a
minute variation in temperature of only
0.02'c, which is a fifth of the White and
Cayan's finding. This anomaly could be
due to either the methods employed by
the Scripps study, or as North points
out, it could be the interaction between
the ocean and atmosphere, which
increases the temperature in the
process. The scientists from the Scripps
Institution supported the latter theory.
They explained that since it was the
equatorial and easternmost parts of all
the ocean basins which showed greatest
evidence of the interaction between the
sunspot cycle and ocean, to move away
from this region would mean recording
a drop in temperatures.
Another study complementing the
Scripps study was conducted by Judith
Lean. It was based on the sun's behaviour over the last 400 years. Because
developing scales of temperature variation on a century-wise basis would be
difficult, Lean, along with Juerg Beer of
the Swiss Federal Institute for Environmental Science and Technology at
Zurich, Switzerland, and R mond
Bradley of the University of Mass
achusetts, decided to study sun-like
stars. Earlier, the astronomer Sallie L
Baliunas of the Harvard- Smithsonian
Center for Astrophysics in Cambridge,
Massachusetts, had divided these stars
into two categories: those-that appear to
have sunspot cycles and those that do
not. While the former were found to
resemble the sun as it looks today, the
latter were considered reminders of
what the sun must hai@e been like 300
years ago, during the Ice Age, when the
earth experienced a prolonged cold spell.
Taking the wavelengths of the ultra-
violet rays emitted by noncycling stars
as a measure of the faculae, Lean and her
colleagues calculated the abundance of
faculae in these stars. They estimated
that 300 years ago, the sun was dimmer
by 0.25 per cent. Thereafter, relying on
the sunspot records, the scientists
tracked the brightening of the sun over
the next few centuries. This was then
compared with the temperature records
of the Northern Hemisphere and a
strong correlation between the shapes of
the graphs - from the results obtained
- was established. Before the beginning
of the Industrial Revolution and the
emission of greenhouse gases (the period between the years 1610 and 1800),
there was a close correspondence
between the two. This led Lean to conclude that after the Ice Age, 3/4ths of the
warming that took place was due to the
brightening of the sun, even though the
sun has contributed to only 1/3rd of the
rise in global temperatures since 1970.
Lean feels that if the sun did play such
an important part in recent global
warming, the contribution made by the
greenhouse gases to climate change
should be reduced. Their contribution
could be 20 per cent lower than what
had been predicted earlier.
Climatologist T M L Wigley of the
National Center for Atmospheric
Research in Boulder, Colorado, us
does not agree to the amendment of the
theory on greenhouse pollution, but he
feels that Lean's "qualitative conclusions are right". However, he does
not blame the sun too much for the
rising temperatures, observed over the
last 100 years. "I think it is somewhere
between 10 and 30 per cent of the past
warming," he says.
We are a voice to you; you have been a support to us. Together we build journalism that is independent, credible and fearless. You can further help us by making a donation. This will mean a lot for our ability to bring you news, perspectives and analysis from the ground so that we can make change together.
Comments are moderated and will be published only after the site moderator’s approval. Please use a genuine email ID and provide your name. Selected comments may also be used in the ‘Letters’ section of the Down To Earth print edition.