Ocean current changes could cause climate 'flip'

Powerful ocean currents are grinding slowly to a halt, raising the possibility of a catastrophic climate "flip" that could chill Europe and warm New Zealand, startling new evidence suggests.

Scientists have detected evidence of a slowdown in the ocean currents that control climate worldwide, supporting earlier research on the threats of global warming.
Without these currents, parts of the globe are expected to alter dramatically. The climate in Europe would cool significantly, while New Zealand would be warmer and more susceptible to exotic diseases, scientists suggest.

The powerful ocean current system, often known as the ocean conveyor, creates a flow of warm surface water towards the North Atlantic, where it is cooled and sinks to start the circulation of cool deep-sea water throughout the world's oceans.

As part of this process, large "chimneys" of very cold water spiral to the ocean floor, playing a key role in ocean flows.

But Cambridge University ocean physicist and Polar Ocean Physics Group head Professor Peter Wadhams has released research showing the number of these chimneys has declined from about 12 to two as a result of global warming.

Releasing the research to a meeting of the European Geosciences Union in Vienna last month, Professor Wadhams said the disappearance of the chimneys, reducing the circulation of the oceans, would cool the climate of Northern Europe as less warm water flowed to the region.

Other oceanographers have stressed that Professor Wadhams' findings are only one piece of a complex puzzle.

Terrence Joyce, senior scientist in the department of physical oceanography at Woods Hole Oceanographic Institution in Massachusetts, United States, has warned that it is important not to be alarmist, but instead to keep up a wide array of research.

For a dramatic climate change to take place, "a whole bunch of pieces have to fit together", he said. "Certainly this is one of them. We need to keep paying attention, and people are doing that."

Woods Hole is conducting research that measures the path and temperature of some parts of the Gulf Stream.

New Zealand scientists have also been reviewing the potential impact of a change in ocean flows.

National Institute of Water and Atmospheric Research oceanographer Phil Sutton said the scenario had "such catastrophic implications" globally that it was worthy of study and consideration.

"We would expect Europe to cool down by as much as 10C - some people are saying worse - but what will happen in the Southern Hemisphere is a gentle warming."

The South Pacific was cooled by flows from the Antarctic, but "if you turn the tap off", this would result in a gradual warming, he said.

Most research suggested New Zealand could expect to warm by about 2C, with some estimates suggesting this could happen within decades.

"Two degrees does not sound like a lot, but it could have a big effect on things like glaciers and snowfall and farming practice and horticulture," Dr Sutton said.

Estimates of the period of time before the flows shut down varied from a decade to a century, though some estimates were shorter, he said.

The New Zealand Climate Change Office says temperature rises in this country could have serious health effects, including the emergence of mosquito-borne diseases, particularly in the North Island.

Increased flooding and droughts caused by climate change would also have health, social and economic effects, a 2001 Ministry for the Environment report found.

New Zealand could also have to cope with an influx of refugees from Pacific Island nations less able to cope with the effects of climate change.

An increase in temperature would mean the Canterbury foothills became about 20 per cent drier, while the Southern Alps would be about 25 per cent wetter and experience more snowfall, said another Climate Change Office report.

Flooding could become up to four times as frequent by 2070.

But the news is not all bad. The warmer conditions could also benefit crop and pasture growth.

Climate flip

* Some scientists believe global warming has disrupted the ocean current system that moves warm surface water to the North Atlantic.

* The change would "flip" climate conditions in both hemispheres, making Europe 10C colder and New Zealand 2C warmer.

- NZPA