Sunday, June 19, 2005

"The Big Chill"

TV show; The Science Channel
June 2005
Issue: Climate change

Lots has been said about the global warming vs. next ice age debate. What this show points out, as other sources are beginning to, is that warming may cause an ice age, and possibly quickly.

To understand why that is, I need to briefly summarize a little oceanography for you (if you don't already know):

Normally, the Gulf Stream carries warm tropical water from the coast of South America north along the US coast, then across to northern Europe before losing enough heat to sink to the bottom of the Atlantic in the Barents Sea. At the bottom, it returns to the tropics to repeat the cycle. That's known as the Great Conveyor Belt, or, in technical terms, "thermohaline circulation."

But, as the globe warms, higher than normal quantities of meltwater from high-latitude glaciers and rainwater from rivers flows into the Atlantic and, being fresh water, it's lighter than the salty ocean. It dilutes the Gulf Stream at its northern end and prevents the water from sinking, causing the Conveyor belt to stop running, or at least to drop to the bottom at some more southerly point.

The Conveyor is the primary reason northern Europe is inhabitable at all. As one speaker on the show noted, it carries about "one million power stations" worth of heat to a part of the world that's at a latitude where Canada has polar bears and Siberia gets winter temps of -40 C on a regular basis. Look at a world map -- or, better yet, a night-time photo -- and you see a striking difference between Europe and other places at the same latitude: Europe is a beehive of cities, home to nearly 500 million people, while the rest of that strip of Earth (except eastern North America)is almost vacant by comparison. (I know the photo seems fairly bright, but a lot of the brightness in western Canada and Siberia is not from cities, it's from oil fields burning off natural gas.)

Right now, annual temperatures are rising, but how much is still debatable; climatologists predict a change of 1.5 to 6 C by 2100, and governments worldwide are to some degree planning for the effects of that heat. But, if this branch of research is accurate, the warmth will be temporary, followed in short order by a rapid cooldown that could last centuries.

Scientists have been finding that Barents Sea salinity is dropping, causing "the largest and most dramatic oceanic change ever measured in the era of modern instruments," according to the US Woods Hole Oceanographic Institute, which led the research. London's Independent newspaper, from which the above quote was taken, says this would cause "a nightmare scenario where farmland turns to tundra and winter temperatures drop below -20C" in Britain. The paper reports (link added):

When the Gulf Stream abruptly turned off about 12,700 years ago, it brought about a 1,300-year cold period, known as the Younger Dryas. This froze Britain in continuous permafrost, drove summer temperatures down to 10C and winter ones to -20C, and brought icebergs as far south as Portugal. Europe could not sustain anything like its present population. Droughts struck across the globe, including in Asia, Africa and the American west, as the disruption of the Gulf Stream affected currents worldwide.

Now, it seems really counter-intuitive to assume heat causes freezing, and that's where research by Thomas F. Stocker comes in (emphasis added):

He and colleague Andreas Schmittner looked at the problem through experiments with a simple, coupled atmosphere-ocean climate model in which a final carbon dioxide concentration of 750 ppm was attained over different time spans. They found that the thermohaline circulation weakens when the increase in carbon dioxide to 750 ppm is relatively slow, spanning several centuries or more. However, when the rate of increase in atmospheric greenhouse gases (expressed as CO2) is similar to today's rate of growth (1% per year)--or the concentration of 750 ppm is reached in 100 years--the thermohaline circulation permanently shuts down.

Hmmm... It permanently shuts down. That's not too encouraging, is it? I suspect he means for the foreseeable future, centuries or millennia, not for the rest of Earth's lifespan, but that's a detail that would make no difference as far as humans go.

Despite the fact that the Bush II administration seems to be ignoring, even demonizing, climate research, the US Defense Department shows some signs of taking it seriously. (Of course... this admin focuses everything on military issues, rather than all the other effects such a problem could have...) In a report by Peter Schwartz & Doug Randall, they found that, "With inadequate preparation, the result could be a significant drop in the human carrying capacity of the Earth's environment."

Schwartz & Randall admit their scenario, which is based on the events that caused a century of cooling 8200 years ago (and thus would NOT be as severe as an ice age), is "not the most likely, but (is) plausible." Overall, they predict, such a cooling could spark wars over food and water supplies and severely restricted energy availability due to frozen ports and increased storminess. "Unlikely alliances could be formed as defense priorities shift and the goal is resources for survival rather than religion, ideology, or national honor."

While reviewing the history, they note that at least eight sudden temperature drops have occurred over the past 730,000 years, and note that a drop like one of the most recent, the Younger Dryas (c. 12.700 yrs ago) or the Little Ice Age (CE 1300-1850), would have a much more serious effect on humans now than then because of our much greater population and, I'd add, the fact that so many people are not living off the land directly.

Their model falls between the two in severity, but still predicts "mega-droughts" in parts of Europe and Asia and less severe droughts in America and elsewhere that "overwhelm available (water) conservation options." Europe's climate becomes "more like Siberia's" within the first decade. Crop yields and growing season lengths in key agricultural areas, including the US but possibly not Australia, "fall by 10-25 percent." Social unrest and wars occur, especially in nations already under economic and political stress, as a "more severe have, have-not mentality" takes over.

"With 815 million people receiving insufficient sustenance worldwide, some would say that as a globe, we're living well above our carrying capacity (already)..." they write. I'm one of those people, as I've mentioned in previous blog entries. But I'm also semi-optimistic; I hope we as a species can realize that such a climate change can best be handled through cooperation, not conflict. But they predict the US and Australia will turn inward, creating fortress nations that keep our supplies for ourselves, while keeping out hungry folks from elsewhere.

...More to come on this, I'm sure...

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