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Interviewer: Earth's rising seas are some of the most visible signs of our warming planet

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over the last 20 years NASA satellites, air borne missions, and field campaigns have shown

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a steady rise in global sea levels as the world's polar ice sheets melt.

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Here to tell us more about this is Dr. Tom Wagner from NASAs Goddard's Space Flight

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Center. Start by telling us you know you have some new images. What are these new

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images show us about sea level rise? Dr. Wagner: You know they show us two really

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important things; you know and first thing is this, sea levels are rising around

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the world and in the last 20 years they've risen by over 3 inches

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on average. And we know this number really well, it's actually recorded by a number of

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different satellites that go over the Earth and bounce radar signals off the ocean

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to determine its height. The other amazing thing though is that the ocean has

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topography. You know you can almost think of it like a mountain range with peaks and valleys.

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And the coast of California in this case actually is a little bit of a valley right now

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and this is caused by a combination of wind and ocean currents. But what people really

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need to take away is that sea level is rising and it's going to continue to rise and it's rising enough

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that it's already impacting us.

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Interviewer: What's causing

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sea levels to rise? Dr. Wagner: What's causing sea level to rise are two basic things. One is that

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as the planet warms up the volume of the ocean expands

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and that's about half of the sea level rise. The other half comes from

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melting of ice that's on land. In particular the glaciers and ice caps of Alaska and

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Canada and also the major ice sheets of Greenland and Antarctica.

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And we have this other amazing satellite called GRACE which actually allows us to

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map changes in the weight of the ice sheets. And what we found is that in the Greenland

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case, we're not only losing ice but the ice loss seems to be accelerating

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and that's something that we're trying to account for in our models as we move forward.

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Interviewer: What is NASA doing to understand how much sea level could rise in the future?

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Dr. Wagner: NASAs doing three basic things you know one is we're developing the technologies

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to study sea level rise and then we're deploying them on

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satellites and also on aircraft to measure how fast the oceans going up.

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But we're also trying to understand the processes that are driving the ice loss and that's why

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we put scientist out in the field to study what's going on with the ice itself. Both

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on the ice and in the oceans around the ice cause that's an important factor. And then

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finally we pull all that data together into models and those models are

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important for us to understand the processes of ice loss and also to do the forecast

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into the future to kind of produce those numbers that society needs to

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plan for 10, 50, 100 years after. Interviewer: So where can we learn

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more and see some of these images. Dr. Wagner: One of the best place to go is

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nasa.gov/earth where you can learn all about the work that we're doing right

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now, the data sets, that are available to see, and also learn about other NASA programs

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studying the Earth.