September 02, 2003

Not just warmer: it's the hottest for 2,000 years

(8/31/03) From America's best newspaper, the U.K. Guardian:
"The earth is warmer now than it has been at any timein the past 2,000 years, the most comprehensive studyof climatic history has revealed. Confirming the worst fears of environmental scientists, the newly published findings are a blow to sceptics who maintain that global warming is part of the natural climatic cycle rather than a consequence of human industrial activity...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."

http://www.guardian.co.uk/climatechange/story/0,12374,1032984,00.html

Not just warmer: it's the hottest for 2,000 years

Widest study yet backs fears over carbon dioxide

Ian Sample, science correspondent
Monday September 1, 2003
The Guardian

The earth is warmer now than it has been at any timein the past 2,000 years, the most comprehensive studyof climatic history has revealed. Confirming the worst fears of environmental scientists, the newly published findings are a blow to sceptics 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 centre 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 metres," 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 Centre. "If you look at the
natural ups and downs in temperature, you'll find
nothing remotely like what we're seeing now."

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.


Posted by richard at September 2, 2003 10:12 PM