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The Decade After Tomorrow March 15, 2010

Posted by Jamie Friedland in Climate Change.
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News stories of massive icebergs breaking off from Antarctica are becoming more and more common.  In late February, a 1000 square mile iceberg slowly rammed the weakened front of the Mertz Glacier in Eastern Antarctica, breaking off a second iceberg of roughly equal size (pics).  There are now two gigantic blocks of ice floating in the Southern Ocean, each the size of Rhode Island and 1,300 feet thick.

Why should you care?  There are a number of environmental concerns raised by events like this, but I find the implications for global water circulation most interesting.  What follows is a little technical, but I will try to explain this fascinating phenomenon clearly.

Ocean currents flow around the planet in a consistent cycle that is dependent upon water density.  Ocean water density is affected by temperature and salinity.  Surface water expands in the heat of warmer equatorial latitudes, becoming less dense.  As that water moves towards the poles, it cools, increasing in density.  In certain polar areas, that dense water sinks deeper into the ocean.  The formation of thin sea ice facilitates this sinking because most ice forms from pure water, leaving the salt behind in the remaining, now denser water.  These geographic differences in density, along with the planet’s rotation, wind and tides, power the large-scale, constant circulation of water around the globe that is known as the “ocean conveyor belt” or “thermohaline circulation.” (Thermo = heat, Haline = salt)

Differences in water density power the Ocean Conveyor Belt.

So what does all this have to do with our giant icebergs?  The two icebergs in question are currently in an area known as a “ploynya,” where thin sea ice normally forms.  Should they remain there, there is concern that they will disrupt the normal operation of the ocean conveyor belt by preventing the salinity increase that accompanies new sea ice formation.  Furthermore, as these giant icebergs melt, they will add large quantities of freshwater to the area, further decreasing the salinity and density of the local water.  Less dense Antarctic seawater could cause regional disruption of the ocean conveyor belt.  And that could have serious consequences for many of us.

The movement of water through the oceans is a driving force in the regulation of global climates.  El Nino readily demonstrates this.  Although its causes remain uncertain, we do know a simple warming of the Pacific Ocean is the mechanism that drives the global weather disruptions of El Nino.

The ocean conveyor belt doesn’t just move water through the ocean, it also transfers heat from the equator towards the poles.  That extra heat is largely responsible for the temperate climate currently enjoyed by Europe and, to a lesser extent, North America.  Were the conveyor and its heat transfer to stop, it has been theorized thataverage temperatures in parts of Europe could drop by as much as 20 degrees F.

In the 2004 movie “The Day After Tomorrow,” a new ice age developed in a matter of days.  That obviously couldn’t happen, but the premise actually isn’t as far from possible as we might like.  A disruption of thermohaline circulation could cause a cold snap surprisingly quickly – and it already has at least once.

Near the end of the last ice age (the Younger Dryas, for those who care), the planet was finally warming after ~100,000 frozen years.  Yet suddenly, about 12,000 years ago, the planet slipped back into a “geologically brief” (1,300 years) ice age over the course of just a decade!

In this period, the glaciers that carved out the Great Lakes finally melted in modern day Canada to form the immense Lake Agassiz.  It held more water than is contained in all the world’s lakes today.  Scientists believe that a geological event, perhaps the failure of an “ice dam,” freed the water in Lake Agassiz, and enough freshwater flowed into the Atlantic to shut down the ocean conveyor belt.  That is what caused the final phase of the last ice age.

Meltwater from this glacial lake caused the last cold snap. Could meltwater from Arctic glaciers cause another one?

Today, as our planet continues to warm, more and more freshwater is entering our arctic oceans as it melts from glaciers in Antarctica and Greenland.  And we have recently been able to measure that the ocean current that powers the Gulf Stream has slowed by more than 30% since the 1990s… Pretty interesting stuff, huh?

So, sorry that took so long, but that is why climate scientists began to warn of an ice age even as the consensus about global warming was still coalescing.  And those concerns persist today, now that the science of climate change is conclusive (although they are rarely voiced because, without the lengthy explanation you just read, such claims can easily be spun to make climatologists look foolish).  Yet as you now know, global warming and an ice age are not mutually exclusive.

Conservatives dismiss theories like this and call people like me “alarmists” for considering them.  Science has intrinsic uncertainties; this may never come to pass.  But if there’s a fair chance that it could and we have the power to stop it, even that chance is enough to justify preventative action.

I’m a Chicago kid, I like my cold weather.  It’s the rest of you that I’m worried about.

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1. The Decade After Tomorrow « The Political Climate | antarcticas - March 15, 2010

[…] the original: The Decade After Tomorrow « The Political Climate Share and […]


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