Global Warming: Melting Glaciers
Global Warming: Melting Glaciers
Michael Oppenheimer (Professor, Princeton University) gives expert video advice on: Why are most of the mountain glaciers in the world melting?; Are conditions in the Artic different today than they were 100 years ago? and more...
What is a "glacier"?
Prof. Michael Oppenheimer: When snow falls in certain mountain areas it builds up and then the weight of all that snow as it's been converted to ice by the pressure pushes the ice toward lower altitudes. And that accumulation of snow, the conversion to ice, and then the ice pushing to lower altitudes is the glacier.
Why are most of the mountain glaciers in the world melting?
Glaciers exist at a balance between snowfall at high elevation and melting at low elevation. Usually over long periods of time, most glaciers are balanced. What's happened recently is that the melting at low elevation has exceeded the precipitation at high elevation, so the glaciers are slowly receding almost everywhere.
How do we know the melting of these glaciers is so severe?
Many glaciers have been examined in detail - that is, the balance between precipitation and melting has actually been measured - and other glaciers are tracked historically, because they've been an important part of civilization and they're important sources of drinking water in some places, for instance. We know from marks on the terrain where glaciers were 100, 150, 200 years ago and there are many accurate historical records, so we know that glaciers are receding. Glaciers are receding in Switzerland, in Austria, in the tropics of Peru - they're just receding almost all over. The only places where glacial ice is safe right now is the very center of Greenland and the very center of Antarctica.
What two places on Earth are extremely vulnerable to global warming?
One of the two places that I think of as the most vulnerable to global warming are low-latitude regions in the Tropics where global warming is expected to reduce precipitation, reduce runoff in rivers and reduce lakes, thereby making things very difficult for agriculture, and reducing the availability of drinking water, too. The other place I worry about are the polar regions, because warming is greater in the polar regions than it is at other latitudes. The ice-borne region of the globe - with major ice caps, the artic sea ice - are very vulnerable and they're already starting to fray away due to the warming trend that we've seen so far. You may think, 'That's happening over there, that's a long way away,' but when the ice caps melt we will have remarkable consequences to sea level, consequences that will reverberate all over.
Are conditions in the Artic different today than they were 100 years ago?
The Arctic is experiencing a vast climate change and conditions are much different. The summer sea ice pack has retreated by about 25%. We're on the verge of opening up the famed Northwest Passage that Arctic explorers sought for hundreds of years. This is affecting the villages of the people that live in the Arctic. These conditions are affecting the Inuit and the people who live in Alaska. For instance, as the tundra melts things crumble into the tundra. Eventually the biggest threat is that the major ice sheets in the Arctic - such as the Greenland ice sheet - will start to disintegrate due to global warming, causing a potentially catastrophic rise in global sea level. There's still time to stop that kind of outcome, but not all that much.
What is "permafrost" and why is it melting?
In the Far North, the moisture in the ground below the surface is permanently frozen. It yields a very hard layer which, for instance, trucks can drive over in the winter. The trouble is, as the permafrost melts, the ground turns into mush, so anything which is built on this solid icy base now sinks in. You see pictures of telephone poles in Alaska which were stabilized by being driven into the permafrost, like sitting on a granite bases. Now those so-called granite bases are melted away, so the telephone poles are going. That's true of any infrastructure. Ironically, the oil and gas industry used to rely not just on the permafrost, but the the top layer near the surface being frozen for most of the year in order to drive their trucks to the North Slope to be able to extract the oil. The length of the season they can now operate on the North Slope is shrunken, because the emissions of greenhouse gasses from coal, oil and natural gas are warming the Arctic so much.
Why should I be concerned about melting permafrost?
There are two reasons to be concerned about melting permafrost. First of all, melting permafrost makes life unpleasant for the people in places like Alaska or Siberia. But maybe more important, permafrost contains a lot of carbon. The ground that is frozen contains a lot of carbon, and as the permafrost melts, some of that carbon then starts to interact with oxygen in the atmosphere, or bacterial activity starts to happen in the soils that was otherwise camped down by the permafrost. That creates methane and carbon dioxide, which get back into the atmosphere and further accelerate global warming; and that's called a positive feedback. So the melting of permafrost is not only an ecological problem and a problem for infrastructure, but actually may further accelerate global warming.
What is the "Larsen-B ice shelf" and why is it breaking up so rapidly?
In Antarctica, the glaciers flow off the continent and they form a little lip which floats on the ocean nearby, and that little lip, that floating lip of ice, is called an ice shelf. Ice shelves don't cause sea levels to rise themselves when they disintegrate because they're like the ice cubes in a glass of water; they just melt away and the level stays the same. However, they do have an important function which is that they jam the ice behind them onto land. They apparently are so jammed onto the edge of the continent that they block the ice in the glaciers on land from flowing into the sea. If you took a bottle of ketchup, put it on its side, and took off the cap, that's a lot like what happens to the ice in Antarctica if you melt or disintegrate the ice shelves. It's like taking off the cap. What's happened to the Larsen ice shelf is that a chunk of it the size of the state of Rhode Island disintegrated a few years ago all in the space of a few weeks due to melting at the surface. It's then allowed the glaciers to run into the ocean and those glaciers, because they're on land and not floating on the sea, actually contributed in a measurable way to sea level rise. Now, it's not a catastrophic thing, but there are much larger ice shelves farther to the south of Antarctica which are buttressing, penning in, or capping much larger glaciers called ice streams. We're concerned that if the warming proceeds to the south and knocks out those bigger ice shelves, then we'll see a very large sea level rise; one that could reverberate worldwide and really have catastrophic consequences.
Why is West Antarctica not as stable as East Antarctica?
The West Antarctica issue, which contains enough ice to raise sea level about seventeen feet, sits on top of bedrock that's below sea level. The ocean isn't frozen, it's melted, so where the ocean comes in contact with ice in West Antarctica there's a lot of melting going on. And the concern is that as global warming proceeds and as the ice shelves disintegrate and as the water in the oceans warms further, it will start to eat into that ice in Western Antarctica, get into that part of the basin that the ice sits on that's below sea level and leak under the ice, and literally lift it off the continent of West Antarctica. That could cause a sea level rise that we just are not prepared to deal with.
What is "meltwater" and why are scientists concerned about it?
On the surface of ice shelves during the summer, in some places, we get pond water, because the sun is strong and the temperatures get elevated a little bit. The ice starts to melt even in cold places. The pond water apparently seeps down through cracks in the ice and eventually causes the ice shelves to disintegrate. If the ice shelves are really the major factor that's holding back the flow of ice from the continent into the ocean, then that meltwater ultimately could be the process that triggers a very substantial global sea level rise.