Atlantic Multidecadal Oscillation and global warming

Paracelsus · #1 (**permalink**) 12-August-2007, 07:22 PM

Here's another natural cycle that has a major impact ON TOP OF the impact of man-made CO2 and other greenhouse gases. Via 'Science' online: http://www.sciencemag.org/cgi/content/full/317/5839/746

Quote:

Over in the Atlantic, there's the Atlantic Multidecadal Oscillation (AMO) of sea surface temperature. It is apparently driven by the acceleration and slowing of the great ocean conveyor that carries warm surface water into the northern North Atlantic. The AMO's vacillations have been linked to everything from triggering drought in the Sahel and the central United States to alternately suppressing and--in the past decade--firing up hurricanes..Lately, researchers are finding that the AMO may have a stronger influence and a longer reach than they once thought. They knew that the oscillation affected climate around the Atlantic, but some suspected it had also caused a mid-century warming of the Northern Hemisphere or even the globe.

Note that the effects of the AMO were apparent in the data AFTER effects of CO2-induced warming were subtracted out of 20th century temp records.

Note also the following prediction:

Quote:

The Hadley group tested the usefulness of their new prediction model by "hindcasting" the climate of two past decades.... The model successfully predicted the warming of El Niño and the effect of unusually warm or cold waters around the world. An actual forecast starting in June 2005 correctly predicted that natural variability--the appearance of cooler water in the tropical Pacific and a resistance to warming in the Southern Ocean--would offset greenhouse warming until now. But beyond 2008, warming sets in with a vengeance. "At least half of the 5 years after 2009 are predicted to be warmer than 1998, the warmest year currently on record," the Hadley Centre group writes.

My bold.

Whether 1998 was the warmest year on record or just the second-warmest year on record, the point is that this model is accurately predicting global trends in ocean temps and climate events such as El Ninos.

Can't comment beyond this--this is just too frightening and depressing.

The original paper is here, if anybody cares: http://www.sciencemag.org/cgi/reprin...7/5839/796.pdf

Kullat Nunu · #2 (**permalink**) 12-August-2007, 08:28 PM

Well, one has to hope they're wrong.

Possible ice-albedo feedback in the Arctic Ocean hardly improves the situation:

Quote:

This July's major loss of sea ice will amplify sea ice loss the remainder of the summer, due to a positive feedback loop. As sea ice melts in response to rising temperatures, more of the dark ocean is exposed, allowing it to absorb more of the sun's energy. This further increases air temperatures, ocean temperatures, and ice melt in a process know as the "ice-albedo feedback" (albedo means how much sunlight a surface reflects). The July 2007 ice loss may mean that a runaway "ice-albedo feedback" has taken hold, which will amplify until the Arctic Ocean is entirely ice-free later this century. Other scientists will disagree, but I believe that such a runaway ice-albedo feedback has taken hold.

Previous winter was weird in the northern hemisphere because the ocean got its ice cover unusually late. Cold air mass that flows from the Arctic dropping temperatures in lower latitudes forms over Arctic ice. One has to wonder what kind of winters we will experience when ice coverage has gone. It will have a major impact on global climate.

Paracelsus · #3 (**permalink**) 12-August-2007, 09:43 PM

Quote:

Originally Posted by Kullat Nunu

Well, one has to hope they're wrong.

Previous winter was weird in the northern hemisphere because the ocean got its ice cover unusually late. Cold air mass that flows from the Arctic dropping temperatures in lower latitudes forms over Arctic ice. One has to wonder what kind of winters we will experience when ice coverage has gone. It will have a major impact on global climate.

Yup, I've heard that too. I suspect that we'll have very warm winters.

Big question: what happens to the big north-south ocean currents such as the Gulf stream when the temp diff between poles and equator decreases? We may not need a big freshwater release from the melted Greenland icecap to nix the Gulf stream.

korjik · #4 (**permalink**) 13-August-2007, 06:50 PM

The gulf stream is probably one of the biggest circulations that warm the poles. If the poles are warmer the 'stream should be weaker, but that would cool the poles making the 'stream stronger, and so on.....

The reason they talk about a freshwater event is that would forcibly stop the circulation, and if the disruption is strong enough, it wont restart.

Last I heared, the disruption of the gulf stream would probably freeze alot of northern europe.

One last thing. Paracelsus, the natural effects come first. The have been there much longer than man's contribution to the global climate. The effect of man made CO2 is on top of the Atlantic oscillation, not the other way around.

Paracelsus · #5 (**permalink**) 13-August-2007, 07:05 PM

Yup, korjik, you're right! Consider that part of my first post amended and thanks for the correction.

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