http://www.commondreams.org/headlines03/0901-01.htm
Published on Monday,
September 1, 2003 by the Guardian/UK
Not Just Warmer: It's the Hottest for
2,000 Years
Widest study yet backs fears over carbon dioxide
by Ian Sample
Also See:
http://www.commondreams.org/headlines03/0829-02.htm
Bush Administration: Carbon Dioxide Not a Pollutant
http://www.commondreams.org/headlines03/0806-01.htm
Global Warming May Be Speeding Up, Fears Scientist
The earth is warmer now than it has been at any time in the
past 2,000 years, the most comprehensive study of climatic
history has revealed.
Confirming the worst fears of environmental scientists,
the newly published findings are a blow to skeptics who
maintain that global warming is part of the natural climatic
cycle rather than a consequence of human industrial activity.
Prof Philip Jones,
a director of the University of East Anglia's
climatic research unit and one of the authors of the research,
said: "You can't explain this rapid warming of the late 20th
century in any other way. It's a response to a build-up of
greenhouse gases in the atmosphere."
The study reinforces
recent conclusions published by the
UN's intergovernmental panel on climate change (IPCC).
Scientists on the panel looked at temperature data from up
to 1,000 years ago and found that the late 20th century
was the warmest period on record.
But the IPCC's report
was dismissed by some quarters
in the scientific community who claimed that while
the planet is undoubtedly warming, it was warmer still
more than a thousand years ago. So warm, in fact, that
it had spurred the Vikings to set up base in Greenland
and led to northern Britain being filled with productive
vineyards.
To discover whether
there was any truth in the claims,
Prof Jones teamed up with Prof Michael Mann, a climate
expert at the University of Virginia, and set about
reconstructing the world's climate over the past 2,000
years.
Direct measurements
of the earth's temperature do not exist
from such a long time ago, so the scientists had to rely
on other indicators of how warm - or not - the planet was
throughout the past two millennia.
To find the answer,
the scientists looked at tree trunks,
which keep a record of the local climate: the rings spreading
out from the center grow to different thicknesses according
to the climate a tree grows in. The scientists looked at
sections taken from trees that had lived for hundreds and
even thousands of years from different regions and used
them to piece together a picture of the planet's climatic
history.
The scientists also
studied cores of ice drilled from
the icy stretches of Greenland and Antarctica. As the
ice forms, sometimes over hundreds of thousands of years,
it traps air, which holds vital clues to the local climate
at the time.
"Drill down far
enough and you could use the ice to look
at the climate hundreds of thousands of years ago, but
we just used the first thousand meters," said Prof Jones.
The scientists found
that while there was not enough good
data to work out what the climate had been like in the
southern hemisphere over that period, they could get a
good idea of how warm the northern hemisphere had been.
"What we found
was that at no point during those two millennia
had it been any warmer than it is now. From 1980 onwards
is clearly the warmest period of the last 2,000 years,"
said Prof Jones.
Some regions may well
have been fairly warm, especially
during the medieval period, but on average, the planet
was a cooler place, the study found.
Looking back over a
succession of earlier centuries,
the temperature fluctuated slightly, becoming slightly
warmer or cooler by 0.2C in each century. The temperature
has increased by at least that amount in the past 20 or
so years, the scientists report in the journal Geophysical
Research Letters.
"It just shows
how dramatic the warming has been in recent
years," said Prof Jones.
Scientists who do not
believe that carbon dioxide is driving
climate change are unlikely to run up the white flag just yet,
however.
Dr Sallie Baliunas
at the Harvard College Observatory in
Massachusetts, for example, maintains that the recent warming
could all be down to changes in the strength of sunlight
falling on the planet.
She concluded that
during the 20th century, earth went
through a cycle of natural climatic change. According
to her data, from 1900 to 1940 the planet warmed slightly,
then cooled from 1940 until 1970, then warmed up again from
1970 onwards. Given that 80% of the world's carbon dioxide
emissions have been produced since 1940, the expected effect,
if carbon dioxide was causing global warming, would be higher
temperatures not lower, she said.
Dr Baliunas's data
also concluded that the period of warming
between 1900 and 1940 must have been due to natural causes,
most likely increased sunlight hitting the earth's surface,
since carbon dioxide emissions were negligible at the time.
The evidence, she said, pointed to variations in the sun's
brightness being the cause of the planet's warming up, not
carbon dioxide.
But other climatologists
have welcomed the new study
as the most conclusive evidence to date that the increase
in temperature is a result of human activity.
"The importance
of the finding is that it shows there's
something going on in the climate system that's certainly
unusual in the context of the last 2,000 years, and it's
likely that greenhouse gases are playing the major role,"
said Prof Chris Folland of the Met Office's Hadley Center
"If you look at the natural ups and downs in temperature,
you'll find nothing remotely like what we're seeing now."
Debunked: Cold
Water on Climate Claims
Not everyone agrees
that climate change is largely driven
by human activity. Some believe the warming the planet
is experiencing now is part of a natural cycle. Historical
anecdotes are sometimes used to support their case, but
the new study debunks these claims.
· There
were vineyards in the north of Britain
There were indeed
vineyards in Britain in the 10th and
11th centuries, but only 50 to 60. There are now more
than 350 in this country, with some as far north as Leeds.
· The
Vikings went to Greenland
In AD980, Erik the
Red and his crew headed from Iceland
to Greenland, but it wasn't for the good weather. Erik
had been kicked out of Iceland for murder so he took his
crew westward where, they were told, they would find land.
· The
Thames used to freeze over more often
The river's tendency
to freeze over frequently in the
16th and 17th centuries is often cited as evidence that
the climate used to be more erratic. But, according
to the new study, the major cause was the original
London Bridge, completed in the 13th century, which
had very small spans between its supports for the Thames
to run through. The result was that the river was tidal
only as far as the bridge, causing the water to freeze
over. When the bridge was rebuilt to a different design
in the 1820s, the water flowed more easily and therefore
became less prone to ice.
© Guardian Newspapers
Limited 2003
###
