Monday, April 4, 2016

The Demise of The West Antarctic Ice Sheet

On Wednesday, the New York times came out with an alarming article. It said that a new, high-resolution model was showing that the West Antarctic Ice Sheet (WAIS), a massive ice sheet west of the "Transantarctic Mountains" that divides the continent into eastern and western sections, could melt far faster than previously thought, with sea levels rising as much as 6 feet by the end of the century. This is twice as high as what other models, such as those used in the reports given by the Intergovernmental Panel on Climate Change, were showing for a similar emissions scenario.

I am always skeptical of these types of articles. New York Times likely wouldn't publish a story like this if sea-level rise with this new model was a meter or less. That's simply not an exciting story to write. And the problem with publishing these types of articles is that it gives the impression to the public that a significant portion of the scientific community believes that the sea level could rise higher than Russell Wilson by the end of the century when, in reality, this is just one study in a field where a lot of uncertainty currently exists.

Credit: NASA

I minored in oceanography at the University of Washington and was pondering double majoring in it and atmospheric sciences, but I ultimately decided to simply go for the atmospheric sciences major because doing both of these wonderful majors would require me to stay at the UW for two additional years. Still, I took plenty of oceanography classes, and in multiple classes, my professors stressed the importance of the WAIS in deciding how much our sea-level could rise by the end of the century. 

Like many glaciers and ice caps around the world, the WAIS has been shrinking since the end of the "Little Ice Age," and global warming has accelerated this process. However, there is a lot of uncertainty as to how the WAIS will react to warming in the future. This is because large parts of Antarctica, including much of the WAIS, actually lie below sea level due to the massive weight of the ice above the continent weighing it down in a process known as isostatic depression.

Subglacial topography and bathymetry of Antarctica.
Credit: Paul V. Heinrich

As the picture above shows, land generally slopes downward as you go inland in West Antarctica due to isostatic depression. In fact, some inland areas are actually over a mile below sea level. Because of this unique feature, the ice sheet is unstable, meaning that even a little bit of a retreat of the WAIS could start a destabilization process that would lead to a collapse of the WAIS. Our current computer models do not have the capabilities to simulate this process, and significant uncertainty in the scientific community exists as to how quickly the WAIS will continue to melt, and if there ever will be a catastrophic collapse of a large section of the ice sheet.

As such, sea-level rise estimates span a pretty darn wide range, even for given "emissions forecasts" looking into the future. As shown below, there is a degree of overlap between the sea level rise with RCP 8.5 (the high-emissions scenario) and RCP 2.6 (the low-emissions scenario), suggesting that there is considerable uncertainty in how much the sea level will rise over the next century. And much of this uncertainty has to do with our poor handle on how the WAIS will behave in the future.

Credit: IPCC 5th Assessment Report

The New York Times article was based on this study on the "Contribution of Antarctica to past and future sea-level rise recently published in Nature. In the study, scientists showcased the results of a new, high resolution model that attempted to correctly model the response of the WAIS to subtle shifts in temperature. With this model, scientists were able to correctly reproduce the sea levels around 125,000 years ago, which are estimated to have been between 20 and 30 feet higher than today. Once they modeled this correctly, they used this model to forecast how the sea level would change in the future. According to the study, Antarctica alone has the potential to contribute one meter of sea-level rise by 2100 and over 15 meters (50 feet!) by 2500 if we continue to pump greenhouse gases into the atmosphere at the current rate.

Credit: Deconto and Pollard, 2016

Even more startling is the predicted rate of sea-level-rise. Since 1950, the sea level has been rising at about an inch per decade. Under the high-emissions (RCP 8.5) scenario, this new Antarctic model predicts that sea levels could rise as much as a foot per decade by the middle of the 22nd century. This would have tremendous impacts around the world, and while many large cities such as Miami, New Orleans, and New York City would be able to adapt to the increasing sea levels, it would be cost-prohibitive to build a seawall around the entire United States to protect all coastal areas from flooding. Donald Trump likes walls, but I believe our biggest threat in the future is from the ocean, not from our neighbors to the south. Developing countries would have an even harder time adapting.

Even though this all sounds very scary, it is important to remember that this is just one study. It is a very important study because it offers new insight into the fate of the WAIS, but in the coming years, more accurate, higher resolution models will be created, and we'll see if they come to similar conclusions. One thing is for sure - we need to decrease our CO2 emissions immediately, because we are just digging ourselves into a deeper and deeper hole. Honestly, when you consider the impact on future generations, I think it is quite selfish of us to be as lackadaisical as we have been. Global warming can't be avoided, but it can be mitigated. 

My challenge to you is to think about one thing you could do every day that would reduce your carbon footprint. Maybe it's taking the bus instead of driving to that doctor's appointment, or maybe it's wearing a sweater in the winter and turning down the thermostat a bit. Maybe it's simply going for a walk instead of watching TV, or maybe it is educating other people about climate change, ocean acidification, and sea level rise. Although our individual impacts on Earth's climate are negligible, we are having a profound impact on the Earth as a whole, so if we could all just work together to try and decrease that impact, that would be awesome.

Thanks for reading!!!

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