Saturday, September 22, 2012

Arctic Sea Ice: What, Why, and What Next

http://blogs.scientificamerican.com/guest-blog/2012/09/21/arctic-sea-ice-what-why-and-what-next/

By Ramez Naam | September 21, 2012

On September 19th, NSIDC, the National Snow and Ice Data Center, announced that Arctic sea ice has shrunk as far as it will shrink this summer, and that the ice is beginning to reform, expanding the floating ice cap that covers the North Pole and the seas around it. The Arctic Sea Ice extent this September was far smaller than the previous record set in 2007. At 3.4 million square kilometers of ice coverage, this year’s Arctic minimum was 800,000 square kilometers smaller than the 2007 record. That difference between the previous record and this year’s is larger than the entire state of Texas. An ice-free summer in the Arctic, once projected to be more than a century away, now looks possible decades from now. Some say that it looks likely in just the next few years.

What’s happening in the Arctic? Why is it happening? And does it matter for the bulk of us who live thousands of miles away from it?

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When scientists and reporters talk about an ice-free Arctic, they’re usually speaking of the Arctic in summer, and especially in September, when ice coverage reaches its minimum.

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As recently as a few years ago, most models of the Arctic ice anticipated that summers would remain icy until the end of the 21st century, and well into the 22nd century. But the trend line above makes that look unlikely. The amount of ice remaining, this year, is about the same as the ice lost between the mid-1990s and today. If ice loss continued at that pace, we’d see an ice free summer sometime around 2030, give or take several years.

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On the other end of the spectrum are those who think the melt could happen much sooner. Peter Wadhams, who leads the Polar Ocean Physics Group at the University of Cambridge, has predicted since 2008 that the Arctic ice could be gone in summer by 2015. He now believes there’s a chance that it could happen even sooner.

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In 2011, a team led by Chilean scientist Christophe Kinnard published a paper in Nature that used data from 69 sites around the Arctic to reconstruct the extent of the ice over the last 1450 years – all the way back to the 6th century AD. What they found was that late summer ice coverage over that entire fourteen and a half century period stayed between 9 million and 11 million square kilometers, a little higher than it was before satellite observation started in 1979, or roughly three times the minimum that we hit this September.

Kinnard was kind enough to send me the team’s underlying data. Combining it with satellite based observations from 1979 onward, the last few decades pop out. Ice coverage fluctuates for centuries, but stays in a narrow band, until suddenly, in the last few decades, the amount of ice left in late summer plunges.

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All the sea ice loss, including that before satellite observation occurred, has happened since the start of the industrial revolution, and the beginning of human emissions of CO2 and other greenhouse gases on a massive scale.

In this context, random variations look rather small. In fact, there are at least three distinctly non-random factors leading to the disintegration of the ice.

1. A Warming Planet. .....

2. Positive Feedback. .....

3. Thin Ice. .....

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When we look at volume instead of area, we don’t see that half of all the ice has disappeared since 1980. Instead, we see that almost 80% of the September ice has disappeared in that time. And most of that loss has been in the last 12 years. 70% of the ice volume we saw in 2000 has disappeared. Less than one third of that ice volume – from just 12 years ago – is what we see today.

If the Arctic sea ice loses volume at the same rate that it has over the last 12 years, then the first ice-free Arctic day in September could happen in the next 5 years. If the rate of ice volume loss continues to accelerate, as it has been, then that day could be even sooner. Ice volume tells a story much more like that of Peter Wadhams, the leader of the Polar Ocean Physics Group at Cambridge, who for years has been predicting an ice free Arctic September as early as 2015.

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The Good News

So is this the end of the world? Or is it just an interesting but ultimately unimportant phenomenon we get to observe? Could it even be an opportunity?

First, some good news. The melting Arctic ice will not cause sea levels to rise to any noticeable degree. The Statue of Liberty isn’t about to be reduced to a head and single upraised arm, forlornly holding her torch just above water. The Arctic ice cap is sea ice. It floats already.

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More good news, or at least the absence of terrible news: The melting Arctic ice is unlikely to suddenly stop the “deep ocean conveyor”, the current that brings warm water to Europe and keeps the continent – much of which is at the same latitude as Canada – fairly warm and temperate. While the deep ocean conveyor belt, also known as the thermohaline circulation, does appear to be slowing a bit, calculations show that the amount of fresh water needed to stop it is far greater than the amount of water currently trapped in Arctic ice.

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The Bad News

1. More Extreme Weather .....

2. Accelerated Warming .....

3. The Arctic Methane Bomb .....

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“Hope for the best,” goes the English proverb, “but prepare for the worst.”

Let’s hope the Arctic sea ice stabilizes, or reverses course. But let’s not count on it. An ounce of prevention is worth a pound of cure. Every step we take to cut greenhouse gas emissions today is far easier than fighting the triple whammy we could be facing just a few years in the future.

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