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Global warming could lead to fast freeze, warns University of Ulster scientist

May 25, 2004

Dramatic climate change as a result of global warming could happen in a single lifetime - instead of being a slow process evolving over centuries, according to a University of Ulster academic.

Professor Marshall McCabe of the School of Environmental Sciences said that given the right set of circumstances, "a climate can flip in a lifetime". And the result could be the return of Arctic conditions last seen in the British Isles thousands of years ago.

He said that the North Atlantic ocean, which controls our climate, is very sensitive to change.

For example, a substantial intrusion of fresh water into the North Atlantic from melting ice-caps may trigger rapid changes that could put the UK and Ireland into the deep freeze for centuries.

Professor McCabe, who is Professor of Quaternary Science at the University of Ulster, has found evidence of just such an event 19,000 years ago.

At that time, several ice sheets in the northern hemisphere melted, adding a five metre 'cap' of fresh water to the North Atlantic ocean.

In normal circumstances the ocean overturns constantly. Heat is drawn off from water at the top of the ocean which then sinks and flows south beneath the equator. New, warmer water is drawn northwards.

It is this cycle that gives the British Isles their temperate climate, despite being on the same latitude as Alaska.

But after the icesheets melted into the north Atlantic 19,000 years ago, the fresh water 'cap' was lighter than the salt water, and remained on the surface. This suppressed the normal circulation of deep water flowing south beneath the equator - leading to the return of Arctic conditions to Ireland.

Professor McCabe's research, published in the prestigious journal Science, showed:

There was a rapid rise in the sea level around 19,000 years ago at Kilkeel, Co Down, due to the collapse of ice sheets in the northern hemisphere.

He was able to accurately date this sea level rise by carbon-dating forams, pinhead-sized organisms found on the sea. His research involved testing around 20,000 forams per sample.

The fresh water 'cap' suppressed the circulation of warm surface water from the south to the north Atlantic oceans - leading to thousands of years of Arctic conditions in Ireland and Great Britain.

Professor McCabe said: "Heat is pulled from the tropics to the north. We are on roughly the same latitude as Alaska and if it were not for the circulation of water between the north and south Atlantic oceans we would be frozen.

"But that could happen if the climate was to flip, through increased freshwater in the North Atlantic - as happened 19,000 years ago".

Ulster, University of