Fascinating article in the June 23 issue of Science. A major puzzle of paleoclimatology is why after tens of thousands of years of glacial conditions, recent ice ages have ended with relatively sudden warm ups. Six authors have devised a comprehensive hypothesis as to why. Here is my attempt to summarize the process:

  1. First, you need very large ice sheets around the Northern Hemisphere. These ice sheets are so large that they depress the continents, pushing them down into the Earth’s mantle.
  2. Next, the Milankovitch Cycle plays a role by increasing the amount of solar energy reaching the ice sheets during summer, resulting in large amount of melt water entering the North Atlantic. Sea levels rise worldwide and encourage extensive calving of icebergs from the continental glaciers lining the North Atlantic.
  3. The freshwater and icebergs result in the formation of vast areas of winter sea ice in the North Atlantic, abruptly returning the Northern Hemisphere to glacial conditions with severe winters.
  4. The return of glacial conditions to the Northern Hemisphere affects the atmospheric circulation of the entire planet, in particular causing a southward shift of westerly winds in the Southern Hemisphere that warm Antarctica and encourage the upwelling of carbon dioxide-rich deep water in the Southern Ocean.
  5. The glacial conditions in the Northern Hemisphere last long enough to encourage prolonged off gassing of carbon dioxide from upwelling Southern Ocean deep water, resulting in the crossing of a threshold where there is enough carbon dioxide in the atmosphere to tip the whole planet into a new interglacial warm period.

If this research holds up to scientific scrutiny, it will bear on the current global warming debates. Some have interpreted the rise of carbon dioxide in the atmosphere at the end of the last ice age not as a cause of deglaciation but rather as an effect of deglaciation. These six authors see carbon dioxide as playing a key role in finally bringing to an end the last ice age because carbon dioxide is a greenhouse gas.

Your Comments, Thoughts, Questions, Ideas

KelsiDayle's picture
KelsiDayle says:

That's so interesting, phamilton! If anyone wants to know more about how polar ice affects climate change or read about an guy who does, check out this former Science Buzz article -- Climate Change Detective and Arctic Explorer: Will Steger.

posted on Thu, 07/08/2010 - 9:22am
jing aling ming wing's picture
jing aling ming wing says:

i will tell you how polar ice affects climate change. because if ice is polar then it is climactic and thus affecting the climate in the following ways: by increasing methane gas in theatmosphere, thus improving the climate. also, and in conjuct

posted on Sat, 07/10/2010 - 11:55am
JGordon's picture
JGordon says:

It's always striking to me when I learn more about global climate shifts—it's never so simple as "everything is getting warmer/colder." Some areas get colder, which causes other areas to get warmer, and back and forth until there's an overall change in global climate. It fits with the unofficial motto for the upcoming Future Earth exhibit: It's complicated!

PS—I looked up a few things as I was reading your post, Pat, so I threw in the links I went to.

posted on Thu, 07/08/2010 - 10:55am
Anonymous's picture
Anonymous says:

take the politics out of it and what do you have? 40 years ago the buzz was the threat of a new ice age. Now its global warming and a guilt trip for everyone who uses any energy. The real truth just isn't out there.

posted on Thu, 07/08/2010 - 1:35pm
bryan kennedy's picture

I don't think that you're comment statement really takes the politics out of anything. Actually it just adds emotion without talking about any scientific facts or evidence.

I actually find it quite comforting that our understanding of how climate works has changed over 40 years of scientific study. New evidence, theories, and discoveries in science aren't a sign of ignorance, but rather an integral part of the scientific endeavor.

posted on Fri, 07/09/2010 - 8:48am
Shana's picture
Shana says:

I agree. If knowledge didn't change we would still think the earth was flat and that the sun and planets revolved around it.

Interesting stuff, Pat. It seems like this could also help unravel some of the discussions of what is 'natural' warming/how much is too much/how fast is too fast.

posted on Fri, 07/09/2010 - 9:43am
Louisiana Girly's picture
Louisiana Girly says:

Knowing that the world is somewhere that you cannot only be known as the person that you are, but the " Scientific You", `That you should learn science. ......................... I think that science is the building blocks of the whole world and you should build off it. That is what I think about this comment and I think that it would be awesome to be able to join the science world and to meet great scientists that have made a difference!!!!!!!! WHENEVER I GROW UP I WANT O BECOME MORE SOPHSTICATED AND JOIN THE " sCIENCE wORLD!!! (:

posted on Fri, 07/09/2010 - 12:55pm

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