Global warming can cause global cooling

[Snowy Owl]

Global warming can cause global cooling​

Jeff Poling

Scientists announced in the July 21, 1999, edition of the journal Nature findings that suggest that global warming can sometimes lead to cold weather or even a worldwide freeze.​

Scientists have long known that a severe cold spell occurred after the end of the Pleistocene glaciation, approximately 8,200 years ago (1).

The cause, however, has been a mystery.


The authors of the Nature article write that the centuries long cold spell might have been caused by meltwater from the disappearing glaciers, cooling the North Atlantic.

The Laurentide Ice Sheet covered parts of North America with ice up to two miles thick for more than a million years.

When the Earth began to warm 10,000 years ago, it retreated back toward the poles. The ice sheet left in its wake at least two lakes containing more water than the Great Lakes combined.

In the Hudson Bay, ice held the water in place like a plug in a bathtub. When the plug finally melted, trillions of gallons gushed into the Labrador Sea, flowing out at 100 times the rate water leaves the Mississippi.

The conclusions of the authors are the result of a study by University of Colorado and Canadian researchers who examined evidence of this huge flood in the Hudson Bay region of Quebec and Ontario.

Independent research showed that global temperatures dropped significantly within several hundred years of the flood.

Until this study, nobody could pinpoint if these two events were connected, said the study's lead author, University of Colorado geologist Don Barber. The scientists used radiocarbon dating of clams in the flood sediment, and other evidence, to correlate the two events.

The Atlantic Gulf Stream normally acts like a conveyor belt to deliver warm tropical water to temperate regions.

By adding so much cold fresh water in such a short time, the flood shut down the Gulf Stream, said Richard Alley, a climate expert at Penn State University.

Temperatures in Greenland and Europe dropped by 6 to 15 degrees for at least 200 years, according to ice core data.

The authors conclusions demonstrate how global warming can, paradoxically, provoke a global freeze.

If a modern glacier such as the Greenland Ice Sheet melts as a result of rising temperatures in the next century, it could trigger a similar flood and climate fluctuation, the researchers said.​

Copyright ? 1999 by Jeff Poling. Quotes are from media sources.

 

[tropical]

Re: Global warming can cause global cooling

Thanks Snowy,

I added an "Insurance Journal" article with an more recent 2005 overview, from an previous thread here (post #3). Texts from:

http://www.insurancejournal.com/news/international/2005/12/01/62622.htm

(bold, enlarged text, mine)

The scientific world community stated this fact during the last few years.
___
"As Arctic ice melts and Arctic rivers flow faster - trends which have both been documented - the northern oceans become less saline. Less salinity means a lower density; the waters then cannot sink, so the conveyor weakens. Computer models have predicted that if it turned off completely, Europe would cool by perhaps four to six degrees Celsius (app. 7.2 to 11 F)."

___
From the "Insurance Journal":

International News
Global Warming Could Lower Europe's Temperature; Raise Caribbean's

December 1, 2005
A study from researchers at the U.K.'s National Oceanography Centre has reached a paradoxical conclusion � global warming may cause a lowering of European temperatures, and it could happen very quickly.
The research team's conclusions, as reported in the scientific journal Nature, are based on observations of the Gulf Stream over a period of 50 years. They've concluded that the current is weakening, and, as a result, less warm water, and consequently less heat, is being transferred from the mid-Atlantic towards the North.
While the study focused almost exclusively on possible changes in Europe's climate, it also mentioned a rather ominous consequence for the mid-Atlantic/Caribbean area. The gulf current not only flows north and south, but also in a circle across the Atlantic and back. If less heat is going north, more will be retained in this oceanic movement, which could well result in further raising the water temperature and, as a result, the atmospheric temperature, in the Caribbean and along the southeastern coast of the U.S. That in turn could well increase the frequency and intensity of the tropical storms � Katrina et. al. - that have caused severe damage and loss of life.

The study, a joint project of the U.K.'s National Environment Research Council (NERC) and Project Rapid, a group examining the possibility of rapid climate change, explains that the Gulf Stream operates somewhat like a conveyor belt. It carries warm water north, which gradually cools and sinks, as it gets colder, a process referred to as "overturning."
"It's like a radiator giving its heat to the atmosphere," Harry Bryden from the National Oceanography Centre (NOC) at Britain's Southampton University, said in a BBCinterview.

This cooled water then flows back south at greater depths. NOC researchers concentrated on the colder water, and found that over the last half century, these currents have changed markedly. "We saw a 30 percent decline in the southwards flow of deep cold water," Bryden told the BBC. "And so the summary is that in 2004, we have a larger circulating current [in the tropical Atlantic] and less overturning."

The rapid melting of the Arctic ice cap is apparently affecting the mechanism. As the northeastern branch flows, it gives off heat to the atmosphere, which in turn warms European land. less heat equals less warming.

The Rapid Project's bulletin notes: "If global warming shuts down the Atlantic heat conveyor - known to oceanographers and climate scientists as the Atlantic thermohaline circulation or THC, and to the rest of us somewhat inaccurately as the Gulf Stream," the U.K. in particular and the rest of Europe in general could face a "future of freezing winters, late springs and early autumns.".

The bulletin explained why, as follows: "The ocean is a moderating influence on climate in Western Europe. Warm water from the Caribbean and Gulf of Mexico flows north and east across the Atlantic. Heat from the tropics is released to the atmosphere and makes our climate warmer and wetter than expected from the latitude we're at. Were this flow to stop our winters would become like those at similar latitudes on the shores of the Pacific and western Atlantic. Just a slow-down would have serious consequences. It has happened before. Possibly more than once since the last ice age.
And paradoxically at least one of these events was a direct result of the Earth becoming warmer."

The explanation for that � given by the BBC � is:
"As Arctic ice melts and Arctic rivers flow faster - trends which have both been documented - the northern oceans become less saline. Less salinity means a lower density; the waters then cannot sink, so the conveyor weakens. Computer models have predicted that if it turned off completely, Europe would cool by perhaps four to six degrees Celsius (app. 7.2 to 11 F)."

How soon could this happen? The estimates vary from never � different variables could reverse the process � to very soon, i.e. within 10 years or so, if the melting of the Arctic ice cap increases substantially.
Find this article at:
http://www.insurancejournal.com/news/international/2005/12/01/62622.htm

? 2007 Wells Publishing, Inc.

 

[Polaris]

Re: Global warming can cause global cooling

National Geographic News: NATIONALGEOGRAPHIC.COM/NEWS


North Pole May Be Ice Free for First Time This Summer
Aalok Mehta aboard the C.C.G.S. Amundsen
National Geographic News
June 20, 2008

Arctic warming has become so dramatic that the North Pole may melt this summer, report scientists studying the effects of climate change in the field.

"We're actually projecting this year that the North Pole may be free of ice for the first time [in history]," David Barber, of the University of Manitoba, told National Geographic News aboard the C.C.G.S. Amundsen, a Canadian research icebreaker.

Firsthand observations and satellite images show that the immediate area around the geographic North Pole is now mostly annual, or first-year, ice?thin new ice that forms each year during the winter freeze.

Such ice is much more prone to melting during the summer months than perennial, or multiyear, ice, which is thick and dense ice that has lasted through multiple cycles of thawing and refreezing.

"I would say the ice in the vicinity of the North Pole is primed for melting, and an ice-free North Pole is a good possibility," Sheldon Drobot, a climatologist at the Colorado Center for Astrodynamics Research at the University of Colorado, said by email.

The melt would be mostly symbolic?thicker ice, pushed against the Canadian continental shelf by weather and Earth's rotation, would still survive the summer.

Recent models suggest that the Arctic won't see its first completely ice-free summer until somewhere between 2013 and 2030.

But this summer's forecast?and unusual early melting events all around the Arctic?serve as a dire warning of how quickly the polar regions are being affected by climate change.

Massive Melt

Scientists are particularly interested in the North and South Poles because they are expected to show the most dramatic effects of global warming.

Models predict that the regions will see temperature increases roughly three times as quickly as the rest of the globe because of an effect known as ice albedo feedback, which occurs when highly reflective ice gives way to dark water.

The water absorbs much more of the sun's energy, increasing temperatures and causing further ice melting.

That has been reflected in the satellite record, which shows a gradual decrease in the extent of Arctic ice coverage over the years.

But the North Pole's current plight stems from a much more startling reduction in sea ice that took place last summer. That extensive melt shattered all previous records and destroyed a significant portion of the Arctic's multiyear ice.

"We lost 65 percent of the ice cover in the Northern Hemisphere all in one year," Barber said. "So it was a whopping decrease. We didn't even think it was possible for the system to lose so much ice all at once."

Scientists say the record loss last year was due to a combination of warm ocean currents, fluke winds, and unusually sunny weather. (See: "Warming Oceans Contributed to Record Arctic Melt" [December 14, 2007].)

It's unlikely that such a mixture of conditions will occur again, University of Colorado's Drobot said.

But forecasts for this summer's ice suggest the damage has already been done.

An unusually cold winter had raised hopes for a recovery, but much of the ice that formed froze later than usual, ending up so thin that it has already started to break up.

"Endangered Species"

Scientists are hesitant, however, to offer a definitive prediction specifically about the North Pole, since that is dependent on weather conditions that are highly erratic.

"Nobody knows for sure," Ron Lindsay, of the University of Washington, Seattle's Polar Science Center, said by email.

"While much of the first-year ice melts in the summer, not all of it does, so we can't be sure it will melt at the Pole," he said. "We also don't know what the winds will be like this summer, and they play an important role in determining just what parts of the Arctic Ocean are ice-free."

But given the rapid changes now evident in the Arctic, the ultimate fate of the North Pole?in fact, all permanent ice in the Arctic?may be all but assured. Almost all models have the Arctic completely ice free in the summer by 2100.

"We jokingly call [perennial ice] an endangered species," Barber said. "It's on its way out. And so we're studying it as quickly as we can, because there isn't going to be any of it left pretty soon."

http://news.nationalgeographic.com/news/pf/32968820.html