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The ocean current that gives western Europe its relatively balmy climate is stuttering, raising fears that it might fail entirely and plunge the continent into a mini ice age. A study of ocean circulation in the North Atlantic, found a 30% reduction in the warm currents that carry water north from the Gulf Stream.
The North Atlantic is dominated by the Gulf Stream – currents that bring warm water north from the tropics. At around 40° north – the latitude of Portugal and New York – the current divides. Some water heads southwards in a surface current known as the subtropical gyre, while the rest continues north, leading to warming winds that raise European temperatures by 5°C to 10°C.
Harry Bryden at the National Oceanography Centre in Southampton, UK, measured north-south heat flow last year, using a set of instruments strung across the Atlantic from the Canary Islands to the Bahamas, found that the division of the waters appeared to have changed since previous surveys in 1957, 1981 and 1992.
From the amount of water in the subtropical gyre and the flow southwards at depth, they calculate that the quantity of warm water flowing north had fallen by around 30%. Previously unanalysed data – collected in the same region by the US government’s National Oceanic and Atmospheric Administration – found a similar pattern.
After warming Europe, this flow comes to a halt in the waters off Greenland, sinks to the ocean floor and returns south. But Bryden’s study has revealed that while one area of sinking water, on the Canadian side of Greenland, still seems to be functioning as normal, a second area on the European side has partially shut down and is sending only half as much deep water south as before. The two southward flows can be distinguished because they travel at different depths. Source: Fred Pearce 30 November 2005 NewScientist.com news service
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Warming reduces rainfall. Two South African researchers are reporting today (3/3/06) in Science that their computer models indicate that by 2100 climate change may rob the south and west of Africa and areas in the upper Nile region of a significant portion of their current water supply. Warming may reduce the rainfall needed to replenish up to 25 percent of Africa's surface water, said Maarten de Wit and Jacek Stankiewicz at the University of Cape Town in Rondebosch, South Africa.
"Water is essential to human survival," they wrote, "and changes in its supply can potentially have devastating implications, particularly in Africa, where much of the population relies on local rivers for water."
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The potential shutdown due to climate warming of the key Atlantic Conveyor current could have a major impact on fish stocks in the region, said Andreas Schmittner of Oregon State University. Oceanographers have predicted that the current that drags warm water from the south to the north could weaken or even come to a halt as global warming melts the Arctic polar icecap and dilutes the ocean's salinity.
"A disruption of the Atlantic circulation leads to a collapse of the North Atlantic plankton stocks to less than half their initial biomass," Schmittner wrote.
To date much work has been done on the potential disruption of the Atlantic Conveyor as the climate warms by an estimated two degrees centigrade this century due to man-made greenhouse gases such as carbon dioxide. However, relatively little research has been published on the possible effect on the seaborne food chain which provides sustenance for millions of people.
"A massive decline of plankton stocks could have catastrophic effects on fisheries and human food supply in the affected regions," Schmittner wrote.
"These model results ... suggest that global ocean productivity is sensitive to changes in the Atlantic circulation," he said. It is not confined to the northern Atlantic but has implications across the Indian, Pacific, Arabian and southern Atlantic Oceans, he added.
Although the effect was most noticeable in the north Atlantic where even a partial weakening in the life-giving current caused a substantial drop in productivity, it also registered globally. Source: Reuters Jeremy Lovell 30 Mar 2005
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Western Europe experienced a very cold climate between 1560 and 1850 that brought dire consequences to its peoples. The colder weather impacted agriculture, health, economics, social strife, emigration, and even art and literature. Storms also had a devastating affect on those that lived near the sea.
In the warmest times of the last 1000 years, southern England had the climate that northern France has now. For example, the difference between the northen-most vineyard in England in the past and present-day vineyard locations in France is about 350 miles. In other terms that means the growing season changed by 15 to 20 percent between the warmest and coldest times of the millenium. That is enough to affect almost any type of food production, especially crops highly adapted to use the full-season warm climatic periods. During the coldest times of the Little Ice Age, England's growing season was shortened by one to two months compared to present day values. LIA
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Rising temperatures are beginning to impact on ecosystems. Butterflies have shifted their ranges northward by 200 km in Europe and North America. Plants lag behind, and larger animals' migration is slowed down by cities and highways. In Britain, spring butterflies are appearing an average of 6 days earlier than two decades ago. In the Arctic, the waters of Hudson Bay are ice-free for three weeks longer than they were thirty years ago, affecting polar bears, which do not hunt on land.
Two 2002 studies in Nature (vol 421) surveyed the scientific literature to find recent changes in range or seasonal behaviour by plant and animal species. Of species showing recent change, 4 out of 5 shifted their ranges towards the poles or higher altitudes, creating "refugee species". Frogs were breeding, flowers blossoming and birds migrating an average 2.3 days earlier each decade; butterflies, birds and plants moving towards the poles by 6.1 km per decade. A 2005 study concludes human activity is the cause of the temperature rise and resultant changing species behaviour, and links these effects with the predictions of climate models to provide validation for them. Grass has become established in Antarctica for the first time.
Forests potentially face an increased risk of forest fires. The 10-year average of boreal forest burned in North America, after several decades of around 10,000 km² (2.5 million acres), has increased steadily since 1970 to more than 28,000 km² (7 million acres) annually. ecosystems
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The new Antarctic measurements, using data from two NASA satellites called the Gravity Recovery and Climate Experiment (GRACE), found that the amount of water pouring annually from the ice sheet into the ocean -- equivalent to the amount of water the United States uses in three months -- is causing global sea level to rise by 0.4 millimeters a year. The continent holds 90 percent of the world's ice, and the disappearance of even its smaller West Antarctic ice sheet could raise worldwide sea levels by an estimated 20 feet.
"The ice sheet is losing mass at a significant rate," said Isabella Velicogna, the study's lead author and a research scientist at Colorado University at Boulder's Cooperative Institute for Research in Environmental Sciences. "It's a good indicator of how the climate is changing. It tells us we have to pay attention." Washington Post
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The Drift Ice is melting -- and the tourist trade with it
MOMBETSU, Japan — The icebreaker Garinko II cast off one recent morning with an apology. The loudspeaker told the four tourists aboard the ship, large enough for 195 passengers, what they had already deduced. Regrettably, the drift ice that drew them here, which usually descends on Japan's northern face this time of the year, was nowhere in sight — a result, experts say, of warming waters in the Sea of Okhotsk.
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Next year, of course, the ice may be thicker and longer-lasting. But some experts say global warming is changing the temperature of the Sea of Okhotsk and shrinking the size of the drift ice the same way it is melting Greenland's glaciers.
Masaaki Aota, director of the Okhotsk Sea Ice Museum of Hokkaido here, said records from the nearby city of Abashiri showed that the average temperature had risen 1.5 degrees Fahrenheit over the last century and that the amount of drift ice had shrunk by 40 percent.
"It's clear that the force of the drift ice has become weaker and the average air temperature has become higher," Mr. Aota said. He said he believed that the most likely cause was global warming, though he added that there was no conclusive evidence. "I don't think this is a problem particular to this place," he said.
The Sea of Okhotsk is the southernmost body of water where drift ice can be seen in the Northern Hemisphere, a phenomenon tied to its twolayer water system. In early December the seawater in the northern Sea of Okhotsk reaches the freezing point as Siberian winds chill the air. At the same time, the Amur River in Russia flows into the sea, glossing the surface with fresh water, which freezes more easily than saltwater.
Temperatures have long been cold enough to freeze the sea's southernmost edge, along the Hokkaido coast, for the first three months of each year. Archaeologists believe that in ancient times the ice allowed Asians from the mainland — known as the Okhotsk people and related to the Inuit in North America — to migrate to Hokkaido.
Here in Mombetsu, a traditional fishing town with a smattering of stores catering to Russians engaging in the crab trade, the drift ice has usually appeared in mid-January and stayed strong until mid-March, often lingering until May. The drift ice made the sea impassable to all ships but icebreakers for an average of 40 days. This year, the sea remained locked for only 10 days.
Takatoshi Hatakeyama, 71, a retired fisherman, remembered that when he was a boy the drift ice invaded the coast every winter. Children played atop the mounds of ice that piled up on the shore.
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For fishermen — especially before it was widely known that the drift ice acted as a lid and contributed to the growth of algae and plankton underneath, to the benefit of fish — the drift ice was considered an enemy. It landlocked fishermen in the winter and forced them to find other jobs during those months. Or it forced large trawlers to break through the ice and seek open waters away from the Sea of Okhotsk.
"The sea would be entirely frozen," said Kazuo Nawata, 69, another retired fisherman. "You couldn't move forward, but you'd have to move forward. So you'd go back, then strike forward, go back, then forward." Norimitsu Onishi, writing for the NYTimes, 3/14/06
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http://zfacts.com/p/237.html | 01/18/12 07:23 GMT
Modified: Sun, 16 Apr 2006 05:50:48 GMT
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