Post from a Scientist: Melting Ice, Raising Sea Levels

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When you pour pancake batter on a griddle, it will spread out. And if you pour too much on the griddle, it will spread right over the edge. That’s exactly what’s happening today in Antarctica, but it’s the ice instead of pancake batter, and the ice flows really, really slowly. When the ice spreads off the “griddle” of the Antarctic continent, it hits the ocean where it floats for a while before breaking off or melting.

I’m a graduate student at the University of Colorado Boulder, and my advisor and I study the floating bits that haven’t broken off or melted yet. We call these floating bits ice shelves. These ice shelves often hit islands or bumps in the bedrock below, which help hold them back the vast amount of ice flowing off the continent behind them. In the last couple decades, a few of these ice shelves have completely fallen apart. We’re studying what made them fall apart, and what could make others fall apart in the future. There are two ways to destabilize an ice shelf: melt it from above or melt it from below. Melting from above happens when the atmosphere warms, leaving big ponds on the surface that can force open cracks. Melting from below happens when the ocean warms, eating away at the underside of the ice.

The ice shelves that have fallen apart so far have been melted from above. They have been relatively small, without much ice behind them. However, some ice shelves that are currently being melted from below are much bigger. If they collapse in the future, it will have global consequences, and our most recent research is showing that some of these shelves are very slowly starting to break. Think about a glass of lemonade in the summer. Every time you add an ice cube to your lemonade, the level of the lemonade rises. If you add too much, it will overflow. Even after that ice melts, the level of the lemonade does not go down, because you’ve just added more water to the glass. If the big ice shelves fall apart, the ice behind them won’t be held back anymore, allowing Antarctica to dump huge ice cubes into our oceans. This will cause the water level to rise and eventually the oceans will overflow onto the land, flooding coastal towns and cities.

Ice shelves are a small but very important piece of our ice systems on Earth. They have major control over our future sea levels, which will affect millions of people around the world.  I encourage you to learn about other parts of our ice systems and how they affect sea level. You can use all the information on this website, or lots of other scientific sources (For example, check out the National Snow and Ice Data Center at www.nsidc.org). We’re working on learning as much as we can, but there is still a lot we don’t know. It’s going to take a lot more work from a lot more scientists before we can predict where you should buy beachfront property in the next few decades!

- Karen, University of Colorado Boulder, USA

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2 Responses to Post from a Scientist: Melting Ice, Raising Sea Levels

  1. Mary W says:

    Hi. I’ve heard that the ice shelves are breaking up faster on one side of Antarctica. Do you know why that is?

    • Karen says:

      Hi Mary,

      You’re corrrect! The short answer is that the shelves are breaking up only in a small area where air temperatures are warm (the Antarctic Peninsula), and there are some that are changing a lot where water temperatures are warm (the Amundsen Sea sector in West Antarctica), but that’s only a small area of the continent.

      Here’s the long answer:

      So far, the only ice shelves that have broken up in Antarctica are on the Antarctic Peninsula. That’s the part of Antarctica that sticks up towards South America – so it’s the part that’s closest to the equator. Because it’s so far north, it has the warmest air temperatures of anywhere on the continent, and the air temperatures are increasing. The ice shelves that have broken up there fell apart because the warming atmosphere caused a lot of surface melt.

      There are also ice shelves in West Antarctica that are melting very quickly due to the presence of warm ocean water melting them from below, but none of these have fallen apart. The Amundsen Sea region in West Antarctica – to the left of the Peninsula, if you look at a map of Antarctica – is the spot that receives the most warm water. The warm water is there due to a variety of factors related to ocean circulation patterns and the shape of the continent and the shallow shelf leading up to it. These are probably the ice shelves that are changing the most, next to the ones that have collapsed on the Peninsula.

      The rest of the ice sheet (East Antarctica) sits on higher bedrock, doesn’t get a lot of warm water, and has relatively cold air temperatures, so overall the shelves there are probably not likely to fall apart anytime soon. There are some pockets that get a significant amount of melt from above or below, but overall the rest of the continent doesn’t have warm enough air or water to cause many changes at this point.

      I hope that helps!
      -Karen-

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