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Global warming impact may be overstated
Last Updated: 7:01pm GMT 10/01/2008
http://www.telegraph.co.uk/earth/ma...rView&xml=/earth/2008/01/10/sciglacier110.xml
Scientists have discovered that glaciers survived for hundreds of
thousands of years during an era when crocodiles roamed the Arctic,
reports Roger Highfield
The most pessimistic predictions of sea level rises as ice sheets are
melted by global warming may have to be scaled back as a result of an
extraordinary discovery that ice persisted when the Earth was much
hotter than today.
Will global warming raise sea levels?
Scientists have discovered that glaciers survived for hundreds of
thousands of years during an extraordinary era when crocodiles roamed
the Arctic and the tropical Atlantic Ocean was as warm as human blood.
They had thought that Earth was ice free during the so called Turonian
period, a "super greenhouse world" between 93.5 million and 89.3
million years ago. But now evidence has been found of hothouse
glaciers that persisted by studies of tiny plankton and other marine
organisms.
Large ice-sheets existed about 91 million years ago, during one of the
warmest periods in the past 500 million years, an international team
of scientists reports in Science.
The scientists from the UK, Germany, USA and Netherlands found
evidence of an approximate 200,000 year period of widespread
glaciation, with ice sheets about 60 per cent the size of the modern
Antarctic ice cap.
The team obtained their evidence from analyses of organic carbon-rich
sediments that were deposited in the western Equatorial Atlantic at
Demerara Rise off Surinam at that time. They contained glassy
carbonate shells of tiny sea creatures, foraminifera. These shells
'captured' the chemical conditions that were present at the time,
providing clues about the temperature, composition and salinity of the
seawater in the hot tub oceans.
By analysing the different types of oxygen atoms (isotopes) in these
shells scientists were able to reconstruct sea temperature, both at
the surface and at depth. Meanwhile, a European team at the
Universities of Newcastle and Cologne in the UK and Germany, and the
Royal Netherlands Institute for Sea Research in the Netherlands
studied the composition of organic molecules from other organisms in
the sediments, providing an independent temperature record of surface
waters for the Cretaceous western tropical Atlantic.
Professor Thomas Wagner, of Newcastle University, says: "Speculation
about whether large ice caps could have formed during short periods of
the Earth's warmest interval has a long history in geology and climate
research, but there has never been final conclusive evidence. Our
research from tropical marine sediments provides strong evidence that
large ice sheets indeed did exist for short periods of the Cretaceous,
despite the fact that the world was a much hotter place than it is
today, or is likely to be in the near future',
Today, the Antarctic ice cap stores enough water to raise sea level by
about 60 metres if the whole mass melted and flowed back into the
ocean. But the new results are consistent with independent evidence
that sea level fell by about 25-40 metres at this time. Sea level is
known to fall as water is removed from the oceans to build continental
ice-sheets and to rise as ice melts and returns to the sea.
Dr Andr
Last Updated: 7:01pm GMT 10/01/2008
http://www.telegraph.co.uk/earth/ma...rView&xml=/earth/2008/01/10/sciglacier110.xml
Scientists have discovered that glaciers survived for hundreds of
thousands of years during an era when crocodiles roamed the Arctic,
reports Roger Highfield
The most pessimistic predictions of sea level rises as ice sheets are
melted by global warming may have to be scaled back as a result of an
extraordinary discovery that ice persisted when the Earth was much
hotter than today.
Will global warming raise sea levels?
Scientists have discovered that glaciers survived for hundreds of
thousands of years during an extraordinary era when crocodiles roamed
the Arctic and the tropical Atlantic Ocean was as warm as human blood.
They had thought that Earth was ice free during the so called Turonian
period, a "super greenhouse world" between 93.5 million and 89.3
million years ago. But now evidence has been found of hothouse
glaciers that persisted by studies of tiny plankton and other marine
organisms.
Large ice-sheets existed about 91 million years ago, during one of the
warmest periods in the past 500 million years, an international team
of scientists reports in Science.
The scientists from the UK, Germany, USA and Netherlands found
evidence of an approximate 200,000 year period of widespread
glaciation, with ice sheets about 60 per cent the size of the modern
Antarctic ice cap.
The team obtained their evidence from analyses of organic carbon-rich
sediments that were deposited in the western Equatorial Atlantic at
Demerara Rise off Surinam at that time. They contained glassy
carbonate shells of tiny sea creatures, foraminifera. These shells
'captured' the chemical conditions that were present at the time,
providing clues about the temperature, composition and salinity of the
seawater in the hot tub oceans.
By analysing the different types of oxygen atoms (isotopes) in these
shells scientists were able to reconstruct sea temperature, both at
the surface and at depth. Meanwhile, a European team at the
Universities of Newcastle and Cologne in the UK and Germany, and the
Royal Netherlands Institute for Sea Research in the Netherlands
studied the composition of organic molecules from other organisms in
the sediments, providing an independent temperature record of surface
waters for the Cretaceous western tropical Atlantic.
Professor Thomas Wagner, of Newcastle University, says: "Speculation
about whether large ice caps could have formed during short periods of
the Earth's warmest interval has a long history in geology and climate
research, but there has never been final conclusive evidence. Our
research from tropical marine sediments provides strong evidence that
large ice sheets indeed did exist for short periods of the Cretaceous,
despite the fact that the world was a much hotter place than it is
today, or is likely to be in the near future',
Today, the Antarctic ice cap stores enough water to raise sea level by
about 60 metres if the whole mass melted and flowed back into the
ocean. But the new results are consistent with independent evidence
that sea level fell by about 25-40 metres at this time. Sea level is
known to fall as water is removed from the oceans to build continental
ice-sheets and to rise as ice melts and returns to the sea.
Dr Andr
