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24 September 2014
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London in an ice age?
BBC Two, Thursday 13 November 2003, 9pm
The Big Chill
Coming Up
Horizon investigates the science behind the Bible Code. BBC Two, 20th November, 9pm.

The Big Chill ­ questions and answers

How does the ocean affect the weather?

Heat transfers readily from ocean to atmosphere, and much of the sun's radiation is absorbed by the ocean. In fact, the upper ten feet (3 metres) of the ocean holds as much heat as the entire atmosphere. Ocean currents move warm surface water away from the tropics and return cold water to them via the ocean floor in a conveyer system. As the surface currents flow, they release heat into the environment, and thereby affect our weather.

How widely accepted is the theory that we could be heading for a climate like Iceland's?

If the ocean conveyer were to shutdown, the Gulf Stream would no longer reach our shores ­ the UK would lose its heat blanket, allowing the full force of winter to hit us ­ in much the same way it does Iceland. If this change were to happen within the next 20 years, Britain would be plunged into the worst winters in living memory. There would be ice storms that break power cables and phone lines. Snow might lie on the ground for a month or more, and temperatures could hit the minus 20's in some regions. Snow drifts might also trap people in their homes. If a conveyer shutdown occurs, our infrastructure would struggle to cope.

Scientists such as Terry Joyce, from Woods Hole Oceanographic Institution in the USA, believe it is likely to happen in the next 100 years. Others simply say that is a possibility that we have to consider.

In 2001, the Government put £20 million into investigating rapid climate change. A programme called RAPID has been set up by the Natural Environment Research Council " improve our ability to quantify the probability and magnitude of future rapid change in climate..."". In addition, large marine research institutions such as the Woods Hole Oceanographic Institute and the Lamont­Doherty Earth Observatory have teams of scientists looking into both what happened during shutdowns in the past and what processes are occurring at the moment.

Why do some scientists disagree with this theory?

Other scientists prefer to describe a rapid regional cooling as a 'low probability, high impact' event ­ so by definition, it might not happen. It is not the most likely outcome of our climate by 2100, but it could have the greatest effect. Scientists who disagree with this theory feel it is most likely that global warming would continue, and Britain's climate would rise by up to 5.8ºC as predicted by the International Panel for Climate Change. This would mean the UK would have a climate more like the south of France's.

If global warming might cause the conveyor to switch off in the future, what caused it to switch off in the past?

The most significant rapid climate change to occur since the end of the last Ice Age is the Younger Dryas period (~11,500 years ago). There are several theories in the scientific literature as to what caused the conveyer to shutdown at that time. One is that the massive Laurentide ice sheet covering much of North America during the last Ice Age melted quickly, and the resulting fresh water was effectively dumped into the North Atlantic, and another talks of vast armadas of icebergs coming down from the pole, melting as they moved south.

There is little doubt among scientists that fresh water is the cause of conveyer shutdown, as it prevents it from overturning. The sources of this fresh water will be different at different times (e.g., depending on climatic conditions), and there may be more than one source, so it has been difficult to show a definitive answer for past shutdowns.

Might the effects of global warming on Britain counter the effects of the conveyor switching off?

The effects of a shutdown would be felt no matter what global warming might bring in the next 50 years. If a shutdown occurs in the next 20 years the cooling effect would be very strong, causing temperatures to fall far below current averages, making Britain a lot like Iceland. Should the shutdown occur in 50 years, global warming will mitigate the effect slightly, but Britain will still end up with a net loss in temperatures. Winters like the 1962 winter, the worst in living memory, could happen around once every 7 years.

If other countries that are on the same latitude as Britain can cope with low temperatures, why would it be a problem for us?

Countries on the same latitude as Britain, but without the warmth of the Gulf Stream, have a very different way of life, having adapted to cooler winters over many centuries. If the shutdown occurs, we would feel the effects very rapidly, and while we could certainly adapt to the change, it's likely that it would take many years. In the mean time our infrastructure would struggle to cope. London came to a standstill in February 2003 due to 2 inches of snow. What would life be like if there were several feet of snow all over the country?

Can we do anything to stop the conveyor switching off, or is it too late?

NERC's RAPID programme aims to "investigate and understand the causes of rapid climate change." While this might not give us the opportunity to prevent a shutdown from happening, it would enhance our ability to monitor and predict future changes, and hopefully mean we can plan for a chilly future.

If the conveyor does switch off, how long would we have to prepare for the change in climate that this causes?

Our clues as to what might happen in the event of a shutdown come from the past. The most significant rapid climate change since the last Ice Age was the Younger Dryas period. Not only did it begin quickly, with temperatures dropping within a few years, but it also ended quickly. It is likely that we would have only 10 years of decreasing temperatures before we get to 5ºC below current temperatures.

Natural Environment Research Council
RAPID programme
BBC Weather Centre
Climate Change
Woods Hole Oceanographic Institute
Abrupt Climate Change
BBC News Online
Global Climate Change
US Geological Survey
National Ice Core Laboratory
The Hadley Centre
Met Office
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