Britain faces big chill as ocean current slows

CLIMATE change researchers have detected the first signs of a slowdown in the Gulf Stream — the mighty ocean current that keeps Britain and Europe from freezing.

They have found that one of the “engines” driving the Gulf Stream — the sinking of supercooled water in the Greenland Sea — has weakened to less than a quarter of its former strength.

The weakening, apparently caused by global warming, could herald big changes in the current over the next few years or decades. Paradoxically, it could lead to Britain and northwestern and Europe undergoing a sharp drop in temperatures.

Such a change has long been predicted by scientists but the new research is among the first to show clear experimental evidence of the phenomenon.

Peter Wadhams, professor of ocean physics at Cambridge University, hitched rides under the Arctic ice cap in Royal Navy submarines and used ships to take measurements across the Greenland Sea.

“Until recently we would find giant ‘chimneys’ in the sea where columns of cold, dense water were sinking from the surface to the seabed 3,000 metres below, but now they have almost disappeared,” he said.

“As the water sank it was replaced by warm water flowing in from the south, which kept the circulation going. If that mechanism is slowing, it will mean less heat reaching Europe.”

Such a change could have a severe impact on Britain, which lies on the same latitude as Siberia and ought to be much colder. The Gulf Stream transports 27,000 times more heat to British shores than all the nation’s power supplies could provide, warming Britain by 5-8C.

Wadhams and his colleagues believe, however, that just such changes could be well under way. They predict that the slowing of the Gulf Stream is likely to be accompanied by other effects, such as the complete summer melting of the Arctic ice cap by as early as 2020 and almost certainly by 2080. This would spell disaster for Arctic wildlife such as the polar bear, which could face extinction.

Wadhams’s submarine journeys took him under the North Polar ice cap, using sonar to survey the ice from underneath. He has measured how the ice has become 46% thinner over the past 20 years. The results from these surveys prompted him to focus on a feature called the Odden ice shelf, which should grow out into the Greenland Sea every winter and recede in summer.

The growth of this shelf should trigger the annual formation of the sinking water columns. As sea water freezes to form the shelf, the ice crystals expel their salt into the surrounding water, making it heavier than the water below.

However, the Odden ice shelf has stopped forming. It last appeared in full in 1997. “In the past we could see nine to 12 giant columns forming under the shelf each year. In our latest cruise, we found only two and they were so weak that the sinking water could not reach the seabed,” said Wadhams, who disclosed the findings at a meeting of the European Geosciences Union in Vienna.

The exact effect of such changes is hard to predict because currents and weather systems take years to respond and because there are two other areas around the north Atlantic where water sinks, helping to maintain circulation. Less is known about how climate change is affecting these.

However, Wadhams suggests the effect could be dramatic. “One of the frightening things in the film The Day After Tomorrow showed how the circulation in the Atlantic Ocean is upset because the sinking of cold water in the north Atlantic suddenly stops,” he said.

“The sinking is stopping, albeit much more slowly than in the film — over years rather than a few days. If it continues, the effect will be to cool the climate of northern Europe.”

One possibility is that Europe will freeze; another is that the slowing of the Gulf Stream may keep Europe cool as global warming heats the rest of the world — but with more extremes of weather.

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http://news.nationalgeographic.com/news/2003/02/0210_030210_englishgarden.html

English Gardens Endangered By Warming?

John Pickrell
for National Geographic News

February 10, 2003

As global warming intensifies, the English country garden as we know it today may soon be a thing of the past, concludes a report issued under the auspices of the United Kingdom Climate Impacts Programme (UKCIP).

The drier summers and milder winters expected to beset the typically cool, rain-drenched British Isles as a result of climate change are likely to negatively impact the lush green lawns, rambling roses, abundant flowering shrubs, and climbing vines that are the defining features of English garden landscapes.

The report was compiled by a coalition of organizations including Britain's Royal Horticultural Society, the Forestry Commission, The Royal Botanic Gardens at Kew, and the UKCIP, a government body established to assess the impact of global warming on Britain.

Although numerous studies have examined the potentially detrimental affects of global warming on agriculture and ecosystems, Gardening in the Global Greenhouse is one of the first to examine the effects of climate change on gardens.

"Some climate change is now inevitable and although we can still influence the extent of this for the latter part of the century, the die is already cast for the next 50 years," said Chris West, a UKCIP scientist. "We want people to find out more about how these changes will affect their lives and to consider this in their plans for the future."

National Obsession

Gardening is the leading hobby in the U.K., and an estimated 27 million people—41 percent of the population—participate in some way. Garden tourism, in a country with many national heritage gardens that are 500 years old or more, is also a big business, estimated to be worth around $480 million annually.

Though estimates of the rate and extent of warming vary, some climate models suggest that temperatures in Great Britain could increase by between 2 to 4.5 degrees Celsius (3.6 to 8 degrees Fahrenheit) by the year 2080, at a rate of 0.3 - 0.5 degrees Celsius (0.5 to 0.9 Fahrenheit) each decade.

The increased temperatures are likely to lead to higher temperatures year-round, and longer, hotter, and drier summers according to the report. Spring flowers and bulbs will bloom earlier and winters will be characterized by a marked reduction in frost and snow and an increase in torrential rainfall and flooding. Snowfall, which is already rare in southern England, may decline by 90 percent in lowland and coastal regions.

In fact, average annual temperatures are rising at such an unprecedented rate that U.K. gardens are already effectively migrating south by 4 to 7 kilometers (2.5 to 4.5 miles) a year, notes the study.

Summer droughts could threaten the herbaceous borders of traditional English cottage gardens. Species including lupin, aster, and delphinium, which require highly moisture-retentive soil, will require more intensive care. Shallow-root trees and hedges such as beech may not be able to adapt to frequent summer dry spells.

Species propagated from bulbs, such as hyacinths, daffodils, snowdrops, bluebells and irises, often require cold winter temperatures to stimulate root development. British gardeners in the warmest areas may have to remove some bulbs and refrigerate them to ensure normal development, said the study.

Other important economic plants such as cherries and blackberries require a winter chill to stimulate growth of flower buds—a situation of concern for the U.K.'s fruit industry as well as home horticulturists.

Consistent Drizzle

The U.K climate is well-known for its moderate temperatures and the "remarkably even" nature of rainfall throughout the year, said Richard Bisgrove, a horticulturist and garden historian at the University of Reading and one of the report's authors.

"The picture of the U.K. as a damp, cloudy, and cool—but not cold—place has been a fair one," he said. However, as summers heat up and winters get wetter, maintaining the flawless lawns Britain is famous for will become increasingly difficult, he said.

Still, the changes might offer British gardeners some interesting new possibilities.

"Gardeners are adept at coping with the weather, and the likely climate change over the next 80 years will present exciting opportunities as well as challenges," said Simon Thornton-Wood, head of science at the Royal Horticultural Society in London. Gardeners may be able to add exotic fruits and sub-tropical plants like citrus and cannas to their repertoire, he said.

Bananas, dates, olives, pomegranates, palms, yucca plants, and other plants not usually associated with the typical English garden may also become increasingly common in the English gardens of the 21st century.

"I already grow my own figs, have grown peaches, and grow grapes and kiwi-fruits in a cold glasshouse, and I look forwarding to growing these outdoors," said Bisgrove.

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