Blog Archive

Friday, September 11, 2009

Glaciologist Marco Tedesco talks about Greenland and Antarctica on the Science Show

Dear Readers,

I think we are all waiting to hear what Dr. Tedesco has to say about the 2009 melt season. Those lakes he referred to in the interview were exponentially larger in 2009 than they were in 2008, with subsequent enormous volumes of melt water draining through the edges of Greenland's ice sheet.

The Science Show -- Marco Tedesco Interview, 2 May 2009

Ice melt in Greenland and Antarctica

Snow reflects about 80% of incoming radiation. Ice reflects just 40%. So ice absorbs more heat. In Antarctica, melting occurs where the ice sheet meets the ocean. In Greenland, there is more melting over the whole ice sheet. Antarctica has experienced major shelf collapse recently. Mark Tedesco describes what it is known about melting over Greenland and in Antarctica and how he collects data in these extreme conditions.

| Hide Transcript


Robyn Williams: Studying ice is complex, both in the south and in Greenland. Marco Tedesco does both, measuring how much ice and snow reflects sunlight, how water flows out to sea or underground, and how you can risk your life on those icy lakes.

Marco Tedesco: The snow reflects about 85%, 80% of the incoming solar radiation, where the ice instead is reflecting about only 40%, which means that if you have a piece of ice and a block of snow side by side, the ice will absorb about 60% of the solar radiation whereas the snow will absorb only about 10% or 15%.

Robyn Williams: So the much brighter snow will send back twice as much sunlight.

Marco Tedesco: Exactly, and also the very new fresh snow is the one that has the highest albedo, which is basically what we're talking about, where as the snow gets older and older the albedo reduces, and because of the crystals getting together, basically hugging each other. So the older snow absorbs more heat and more energy than the younger snow.

Robyn Williams: And therefore melts more.

Marco Tedesco: Yes.

Robyn Williams: So the less shiny you are, the more heat goes in, and you become even more opaque, less shiny.

Marco Tedesco: Yes, exactly. So if you have new snow and suppose you have warming temperatures, then older snow will be more subject to melting, not only because of the temperature but also because it will absorb more solar radiation.

Robyn Williams: That's the theory. What do you find when you actually look at Antarctica and you look at Greenland?

Marco Tedesco: There is a big, big difference, first of all, in the distribution of melting over Antarctica and Greenland. In Antarctica most of the melting occurs over what are called the ice shelves, protruding blocks of ice into the ocean. They are acting as a cork in a champagne bottle for the ice sheet. They also separate the warmer air coming from the ocean with the ice sheet, and that's where most of the melting occurs. The ice shelves, they already stay in the ocean, so when they melt they really do not contribute a lot in sea level rise.

On Greenland instead melting occurs over the ice sheet and melting occurs for longer periods over Greenland than Antarctica, though Antarctica was also subject to very spectacular recent events, like the collapse of some of the ice shelves. Greenland is subject to melting especially along the west coast, which is the part where we are most concerned, for more than three months during the summer. Usually melting doesn't reach high elevations, it doesn't go beyond 1,500 metres. But in summer 2007 we found that melting lasted for more than one month at high elevations above 2,000 metres and this was a new record within the satellite area that we use for observing the phenomenon.

Robyn Williams: A new record. By much?

Marco Tedesco: Usually you have melting there for ten days, the record was 30 days, and in terms of percentage it's about more then three times what usually happens there. In 2008 also we had a new record where melting lasted also for 15, 20 days longer than the average. These areas are also the same areas where we observed some other extreme phenomena like collapse of the Canadian ice shelves, and also the break-up of the Petermann Glacier on the north-west part of Greenland.

Robyn Williams: When you said, with the shelves coming off Antarctica this time...straight into the sea because it's already there...but we've heard of there being huge lakes in Antarctica that have been there practically forever. When the water melts in Greenland on land itself, where does that water go? Does it run off into the sea?

Marco Tedesco: This is the current million-dollar question for scientists actually because we know that this water piles up in big ponds. These lakes can go from a couple of hundred metres to one kilometre wide and about 10 or 15 metres deep, so they can hold a lot of water. The question is, where does this water go? And this is a big question because how this happens is going to really affect the hydrology of the ice sheet.

So there are some theories that suggest that the water can drain along the ice sheet, actually can percolate along the ice sheet and can reach the bedrock thus eventually accelerating the ice sheet by reducing the friction between the ice and the bedrock. And some other colleagues are suggesting that there are main pipe systems that collect most of the water. This water is discharged into the ocean somewhere. Where, how, it's very open. We are actually planning to go there and study some of the lakes and how we can improve their detection using remote sensing techniques.

Robyn Williams: Hang on, you would go onto the lake on a little boat and you would watch it drain..?

Marco Tedesco: It is dangerous. Some colleagues, they did it already. We decided that we are actually scientists and not adventurers...

Robyn Williams: What happened to those colleagues, by the way?

Marco Tedesco: They are back and they were the first ones, so there's no point being the third one and being the one who dies, because these lakes can drain very, very fast, and if you are really there on a boat, no matter what you do you might not able to get out and you'll be becoming part of the ice sheet, which is not something you want to be remembered for! Now our idea is really to find some engineering solutions, and the most recent one is to use radio controlled boats that are somehow hosting and piggybacking basically our instruments, and so they can do the work for us. So if we lose one of those instruments it will be no big deal for us.

Robyn Williams: What happens if you find that the water is flowing out to sea from Greenland? What's the difference between that and its going back into the ice sheet?

Marco Tedesco: We know that there is some water that refreezes when the snow melts. Understanding what the path is will help us to understand the entire plumbing system. There is also of course a loss due to carving of the iceberg and this is volume mass [?], and of course this cannot be done only using remote sensing tools. We are combining our remote sensing tools with climate modelling tools.

Robyn Williams: What about your hunch, the implications for climate change which of course are crucial to what we've been talking about, both Greenland, huge amounts of ice and water, and also Antarctica? What are your feelings about the rate of melting that's going on now?

Marco Tedesco: Well, for Antarctica we are navigating very dangerous waters I think because the trends that we get from Antarctica is not what we call statistically significant, which means that whatever number you're getting in terms of increasing or decreasing melting at most of the places in Antarctica, if you add one year or subject one year, that result might change. So if you have a positive trend like a melting increasing, if this year was very cold, as it was because of La Nina and other factors, that trend might become negative. And this is because of the strong variability and because of course of the size of Antarctica.

On Greenland we have instead statistically significant trends, so we know that there is an increase in melting. The area subject to melting has been increasing about 16,000 square kilometres per year for the last 30 years. So we have areas that are melting every year more and more. Also in 2008 we had some stations recorded a new record in terms of air temperature. So this is how the warming of the Arctic is affecting the melting in Greenland.

In terms of how the Greenland melting can counter-affect the climate is that of course the more melting you have the more water will be produced and then of course you have more contribution to sea level rise. But also you have the albedo mechanism, which means that you will have the Greenland ice sheet absorbing more energy, so it will contribute to eventually absorb more heat for the whole Arctic, so not only the temperature is going to create this condition but also solar radiation that is absorbed by the ice sheet can contribute to even further warming in northern areas and the whole Arctic.

Robyn Williams: So next time you hear about anyone arguing about the growth of ice sheets or sea level rise, think of all those satellites, radar, underground lakes and carving ice shelves. It's a complicated process and one we'll cover in another program coming up featuring the way they're listening to the ice cracking. They're doing that in Perth at Curtin University, and yes you can hear all the way to the southern ice shelf by listening in labs in Australia. But Marco Tedesco does his research at the City University in New York.


No comments: