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Global warming study provides cold comfort for north Europeans

24.06.2005


Global warming could result in northern Europe growing colder as the southern hemisphere gets hotter, according to new research led by the University of Edinburgh. A study, based on analysis of changing climate patterns at the end of the last ice age, confounds the widely-held view that global warming will be uniform across the world. It also suggests that ice age conditions could return to the northern hemisphere sooner than was previously thought.



The research, which claims that the north Atlantic’s relatively warm waters could cool at the same time as the colder Southern Ocean heats up, appears in the Swedish journal Geografiska Annaler. The study is significant because it suggests that major shifts in global climate are influenced not just by atmospheric conditions, but also by fluctuations in ocean currents. The researchers say that a complex climatic ’seesaw’ effect – last triggered when the post-Ice Age earth heated thousands of years ago – could be set off again in our present warming world.

The research team spent 14 years analysing radiocarbon and isotope samples from Patagonia – the most southerly land mass outside of Antarctica – to build an accurate picture of glacier changes there during the past 25,000 years ago. When they compared their results with existing data which mapped north Atlantic glacier changes over the same time period, the scientists reached a striking conclusion. They found that during times of major climate change, glaciers in Patagonia expanded as those in the north shrank, and vice versa.


The idea of such a bipolar seesaw effect has been mooted before, but this study is the first to present firm dating evidence from a southern land mass to support it. The data shows that the seesaw occurred only during the transition from a full Ice Age climate 17,500 years ago to our present non-Ice Age climate, which began 11,400 years ago. Significantly, there was no evidence of the effect taking place in more stable Ice Age and non-Ice Age periods.

With the Earth now appearing to move out of a settled climate period, the findings seem significant. The past 11,400 years of climatic stability have resulted in a warm Europe and cold southern ocean, because the Gulf Stream takes warm water north across the equator. However, the study suggests that global warming could prompt a significant cooling of the north Atlantic and warming of the Southern Ocean if the bipolar seesaw effect is triggered once again. The trigger could be melting ice in the Arctic that cools the north Atlantic, or changing winds and ocean currents around a warming Antarctica.

Project leader Professor David Sugden, of the University of Edinburgh’s School of GeoSciences, said: “Our discoveries raise interesting questions for our present warming world. How stable is our present climate system? How far can it be pushed before we inadvertently switch the bipolar seesaw on or off? Can it be switched on by changes in the southern hemisphere, for example by changes in Antarctica? The study confirms that we may be closer to Ice Age conditions in the northern hemisphere than many previously thought.

“This evidence, which shows north and south acting ’out of phase’ during periods of great change, but acting ’in phase’ during more stable periods presents an interesting puzzle. Perhaps it means that the world’s climatic system is stable and all-pervasive when it is in its Ice Age mode or non-Ice Age mode. Under such circumstances, changes in the atmosphere dominate the world’s climates. It is during the transition from one mode to the other that the climate may become more sensitive to the effects of the seesaw.”

Scientists from the Universities of Durham and Stirling, as well as the Scottish Universities Environmental Research Centre, took part in the Edinburgh-led study.

Rebecca Wray | alfa
Further information:
http://www.geos.ed.ac.uk/homes/des

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