Not
Just Warmer: It's The
Hottest For 2,000 Years
By Ian Sample
The Guardian, UK
02 September, 2003
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.
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