Dec 14 2017

Antarctic Ice

Perhaps one of the most underrated science stories of 2017 was the separation of a massive iceberg the size of Delaware from the Larsen C Ice Shelf in Antarctica. That is because this is not an isolated event, but just a dramatic part of a larger story – the melting of Antarctica.

Antarctica contains most of the ice on Earth (90%). Much of that ice sits on top of land, unlike Arctic ice which is floating. When floating ice melts it just fills the space that it had displaced. There is a little bit a sea rise due to rising temperatures – water expands as it warms. But this amount of sea rise is small overall. When ice that was sitting on land flows into the ocean, it raises the sea level more significantly.

Antarctica is comprised of glaciers sitting on top of the continent, which itself is mostly below sea level. These glaciers are as thick as three miles. They are divided into a western glacier system and an eastern glacier system. West Antarctica, which is melting faster, contains enough ice to raise the sea level by 14 feet. East Antarctica is more stable but still showing some early signs of melting. All the ice here could raise the sea level by 175 feet.

As the glaciers melt during the warmer months they follow channels out to the ocean. These channels, however, are blocked by ice shelves, which act like a cork, keeping back the ice and helping to maintain the stability of the glaciers.

The ice shelves themselves have a certain structure – they rest on the sea floor but as they extend out from the continent eventually the ice lifts off the sea floor (called the grounding point) and as the ice extends out further it is floating on top of the water. The breakup of these ice shelves is a concern, because that would essentially remove the stopper and greatly accelerate the rate at which glacier melt finds its way to the ocean.

What recent research has shown is that warm ocean water is traveling along channels under the Antarctic ice shelves, melting the underside of the shelves and eating away at the grounding point. This is weakening the ice shelves, increasing the rate at which they break up. The giant Larsen C iceberg was a symptom of this phenomenon.

As the ice shelves weaken, the rate at which the glaciers move to the sea is accelerating. Essentially ice forming and melting in the Antarctic has been in a homeostasis, and now that balance has shifted with melting happening faster than ice is being replaced. There seems to be no question at this point that Antarctica is changing. Even without any further release of CO2 or warming, the warming we have already caused has shifted the equilibrium. Some scientists estimate that existing warming will result in a sea level rise of about 10 feet. Of course, further warming will only make this worse.

Really the big question for Antarctica is when – will it be 50 years or 500 years before the ice shelves disintegrate completely and significant glacial ice finds its way into the ocean? There is the possibility of a domino effect, because the ice is holding back further ice. As it collapses, the ice behind it is then unstable and may collapse. Scientists are concerned because much of the increased melting is happening under the surface ice. The ice shelves and glaciers are being hollowed out, forming pockets and streams of water below the surface. At some point the system may collapse.

It is always difficult to warn about possible future calamity. It is easy to come off sounding hysterical, and critics can easily paint you that way, even if you are being sober and careful. Further, with many natural phenomena there is always uncertainty. How bad will an epidemic be? What are the odds of that asteroid hitting the Earth? What will the effects of the Y2K bug be?

The thing is, it is reasonable to prepare for and attempt to prevent possible negative outcomes based upon our best current estimate. It is unreasonable, even folly, to demand near 100% certainty before taking reasonable steps to prevent harm. And of course if you are successful, then the critics can always claim that there was never any risk.

So, we don’t know exactly what is going to happen in Antarctica or when. What scientists can see, however, is that the rate of melting is increasing, the ice shelves are becoming unstable, and this is further increasing the rate at which glacial ice is finding its way to the sea. They cannot see the future, but they can make reasonable inferences and warn about possible threats. It’s good to know what the range of possibilities is – what is the best and worst case scenario. Generally speaking we should prepare for the worst and hope for the best.

You can also take a risk vs benefit approach. What is the risk of doing nothing? What is the risk and expense of taking specific steps to mitigate anthropogenic warming? Obviously you don’t want the cure to be worse than the disease. But let’s take a sober look at the “disease.”

Even a modest 10 feet of sea level rise (modest compared to the potential from Antarctic ice melting) will flood the southern tip of Florida, will flood many coastal cities, and displace millions of people. Further, with rising sea levels storm surges will be much worse. Coastal flooding from storms can be devastating. The cost would likely rise into the trillions. That is not even the worst case.

I think that justifies taking some aggressive steps to mitigate further climate change. Our technology is already heading in the direction of renewable energy sources. They are getting cheaper, they are distributed, and they reduce pollution. They also reduce dependence on a limited resource, one that often comes from unstable parts of the world. Energy efficiency technology saves everyone money, so they are a win-win. Accelerating the development and adoption of superior technology is a no-brainer. It is only being opposed by vested interests in the status quo.

We would do well to heed the warnings of our scientists, especially when there are some obviously beneficial steps we can take.

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