11 April, 2005

Researchers at the British Antarctic Survey (BAS) and the University of California, Santa Cruz have discovered that Earth’s last great global warming period, 3 million years ago, may have been caused by levels of CO2 in the atmosphere similar to today’s.

Reporting this week in a leading Earth Science journal, Geochemistry Geophysics Geosystems, the scientists describe how they tested two widely held ideas that attempted to explain the balmy conditions on Earth at that time. Their findings clearly demonstrate that studying past climates can help us to understand the likely impact of greenhouse gas emissions and global warming.

BAS Principal Investigator Dr Alan Haywood said,
‘There are two schools of thought about past warm intervals. Many scientists suggest that they were caused by ocean currents (like the Gulf Stream) moving greater amounts of warm water from the tropics to the polar regions. Others speculate that increased levels of CO2 in the atmosphere initiated warming all over the planet. We used the latest supercomputing technology combined with chemical analysis of seabed sediments to make a sophisticated reconstruction of past sea temperatures. If the warming was caused by ocean currents, we would expect to see cooling at the tropics and warming at the poles. Conversely, if CO2 was the cause then we would expect both the tropics and the poles to warm. The sea temperature pattern we found points the finger squarely at CO2 rather than the ocean currents. This is a real breakthrough for those of us investigating past climate – we’ve made a major contribution to a long standing argument and our findings are critical to understanding how climate may respond to emissions of greenhouse gases in the future’.

Clues to past sea-surface temperature come from tiny marine algae that live near the surface. They produce chemicals called alkenones that record the sea temperature. When the algae die they sink and become part of the seabed. Therefore, a record of past sea temperatures is stored within the sediments. Sea-surface temperatures were also predicted using a climate model running on a sophisticated supercomputer based at Manchester. This is capable of billions of calculations per second.

Issued by the British Antarctic Survey Press Office.
Linda Capper – tel: ++44 1223 221448, mob: 07714 233744, email: l.capper@bas.ac.uk
Athena Dinar – tel: ++44 1223 221414, mob:07740 822229, email: a.dinar@bas.ac.uk

Picture Editors: Stills of the JOIDES Resolution which is the drill ship used to collect the sediment cores that were analysed are available from the BAS Press Office. Credit: the U.S. Implementing Organization for the Integrated Ocean Drilling Program.

Notes for editors:

“Warmer tropics during the mid-Pliocene? Evidence from alkenone paleothermometry and a fully coupled ocean-atmosphere GCM by Alan M Haywood, Petra Dekens, Ana Christina Ravelo & Mark Williams is published in GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS, VOL. 6, NUMBER 3, doi:10.1029/2004GC000799.

Contacts: Alan M Haywood, British Antarctic Survey, High Cross, Tel: + 44 (0)1223 221420
Mark Williams, British Antarctic Survey, High Cross, Tel: + 44 (0)1223 221427

Petra Dekens and Ana Christina Ravelo, Ocean Sciences Department, University of California, Santa Cruz, California, USA. Tel: 00 1 831-459-3722

British Antarctic Survey is a world leader in research into global issues in an Antarctic context. It is the UK’s national operator and is a component of the Natural Environment Research Council. It has an annual budget of around £40 million, runs eight research programmes and operates five research stations, two Royal Research Ships and five aircraft in and around Antarctica. More information about the work of the Survey can be found at: www.antarctica.ac.uk

University of California Santa Cruz is one of nine campuses of the University of California, and is recognized worldwide for the quality of its research and teaching. UCSC has a strong and diverse group doing interdisciplinary research on coastal environmental change and ocean health within the Center for the Dynamics and Evolution of the Land Sea Interface. More information about UCSC can be found at: www.ucsc.edu.