[lbo-talk] it's getting hotter, really

[Doug Henwood]

[cue to James Heartfield..]

Guardian (London) - September 1, 2003

WIDEST STUDY YET BACKS FEARS OVER CARBON DIOXIDE
Ian Sample, science correspondent

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 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.