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Curious Universe: Earth's Expanding Oceans

Logo graphic for NASA Cruoius Universe

The following is a transcription of a podcast.

Our universe is a wild and wonderful place. Join NASA astronauts, scientists and engineers on a new adventure each week — all you need is your curiosity. Fly over the Antarctic tundra, explore faraway styrofoam planets, and journey deep into our solar system. First-time space explorers welcome.

With Earth's recent record-breaking temperatures, the pace of sea level rise has accelerated. NASA scientists take us on a trip into their research right here on our home planet. Join us as we fly over Antarctic ice sheets and consult with orbiting satellites on this exploration of our changing Earth.

Gavin Schmidt: You know NASA, really, was set up to, to look outwards, but also to look inwards from the outside. The original speech that John Kennedy gave where he set that target to get to the moon in a decade…

[John F. Kennedy Archive: We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal…]

Schmidt: The next bit of that speech was, we're going to start having weather observing satellites to keep track of what's going on.

[Kennedy Archive: Transit satellites are helping our ships at sea to steer a safer course. Tiros satellites have given us unprecedented warnings of hurricanes and storms, and will do the same for forest fires and icebergs.]

Schmidt: It's really part and parcel of the same spirit of exploration, of understanding, of data gathering. Our role as scientists is to help society see what those problems are likely to be, how they're going to manifest and how maybe we should solve them. When you have that view from space… you see things differently.

Patti Boyd: This is NASA's Curious Universe. Our universe is a wild and wonderful place. I'm Padi Boyd, and in this podcast, NASA is your tour guide!

Boyd: NASA might be best known for the work we do in space, but there's a lot here on our home planet we study every day.

Boyd: From increased hurricane intensities and longer fire seasons, to changes in migration patterns and growing season… climate change is impacting the way our Earth functions as an interconnected system.

Boyd: Today, we're going to explore how NASA scientists are tracking and predicting the changes in our oceans.

Schmidt: Hi, my name is Gavin Schmidt. I'm the director of Goddard's Institute for Space Studies in New York City. And since February, I am the senior adviser on climate to the NASA administrator.

Boyd: Scientists know that our home planet is changing due to climate change. Gavin's job is to keep an eye on all of it and identify how each piece of our changing Earth can impact the others. One of those pieces is sea level rise, or the expansion of our oceans along coastlines.

Schmidt: We understand why sea level is rising and the rate it's rising, and it's rising at about three millimeters —a little bit more —per year and accelerating. Because we're increasing the amount of greenhouse gases in the atmosphere, there's more heat coming into the system than is leaving. And that heat has got to go somewhere and that heat is going into the ocean.

Boyd: That 3 millimeters a year rising rate might not sound like a lot, but on average… ocean levels have risen about a foot in the past 100 years. And that change in ocean height is coming from a couple of different sources.

Schmidt: Heat that goes into the ocean makes it warmer and warmer water expands. Half of what we're seeing in terms of sea level rise is just the fact that the water as it warms is just expanding.

Boyd: On a molecular level, warmer water takes up more space than colder water. As all of those tiny, molecular differences add up… the whole ocean expands. We can see that expansion as the now warmer and larger oceans creep up the coastline.

Boyd: But those heated molecules are only one part of our rising oceans. Scientists are also focused on how quickly we are extracting Earth's groundwater….

Schmidt: We're taking out groundwater at unsustainable rates in many places around the world. And when you take groundwater out like that, and you don't replace it, then that water ends up in the ocean as well. We're building lots of dams and reservoirs, and so that's keeping some of the water back.

Boyd: Groundwater is what you might find in a well. It provides a lot of our drinking water. When we pull that water out of the ground, use it, and then return it to the oceans instead of back into the ground, it adds to our rising sea levels.

Schmidt: But then you've got to think about all of the mass of water that goes into the ocean. Because we're melting Greenland, because we're melting West Antarctica, on average, there's water, there's ice, that's falling into the ocean, and that's raising the sea level as well.

Schmidt: The loss of mountain glaciers is accelerating over the last decade and that is actually giving us about 20% of the sea level rise right now, is just the continued retreat of glaciers, in the Rockies, in the Andes, in the Himalayas, in the Alps, pretty much anywhere in the world where we can see ice right now.

Boyd: This is probably the most well-known cause of sea level rise —melting ice. Right now 10% of the Earth's surface is covered in ice. As the temperature of our planet rises, that ice, on average, melts. Those melted glaciers, icebergs, and ice sheets turn into water that fills our oceans.

Boyd: Of course, like most things on Earth, the way our oceans are changing isn't perfectly even.

Boyd: Some places are rising quickly and some are even falling. Scientists are looking at coastal places like New Orleans in the United States and Jakarta in Indonesia, to see how these effects might play out in high-risk areas. If sea levels continue to rise, cities and towns that are currently sitting on a coast… could find themselves underwater.

Boyd: On the other hand, places like Sweden and Greenland are experiencing lowering sea levels. The Earth is a fascinating system and what happens in one place can have strange and far-reaching effects somewhere else.

Schmidt: So that three millimeters a year is not uniform. You've got effects because of the gravity changes. This is really cool, you know, mathematically anyway. If you lose ice from Antarctica, because that ice is now spread out around the ocean as water, the gravity of the system has changed. There's less mass in Antarctica so there's less gravity and so, so the sea level actually falls around Antarctica, but then goes up a little bit more than average everywhere else.

Schmidt: And the same is true for Greenland. If you lose mass on Greenland, it causes the water to go down at right next to Greenland, but goes up a little bit further away. And so you've got these patterns that are associated with gravity and even slight shifts in the rotation of the Earth.

Boyd: NASA is able to track those shifts and patterns from many different vantage points. We have the unique perspective of looking at the Earth not only from the surface, but from the outside, using planes and orbiting satellites.

Boyd: Brooke Medley is a research scientist in NASA's Cryospheric Sciences Laboratory. She studies ice melt on the ground and from the skies.

Brooke Medley: We really want to understand how the ice is changing now. And then can we use that information to evolve into the next century as sea levels rise across the globe. One of the most recent missions that NASA launched is called ICESat-2 and that's a lot of what I'm working on.

Boyd: ICESat-2 is an orbiting satellite, working as part of NASA's Earth Observing system.

Medley: And the goal of ICESat-2 is to actually measure the changing height of the ice sheets. These are very, very thick chunks of ice. If we want to understand how they're changing, we can actually measure how they're thickening or thinning. And we do that extremely precisely, with ICESat-2, down to the millimeter level, because if you have a very subtle change over a very large area, it makes for a really big change.

Boyd: ICESat-2 has been orbiting Earth since 2018 at around 300 miles above the surface. Even from way up there, ICESat-2 can measure how ice is increasing or decreasing here on Earth. The satellite uses a finely-tuned instrument that times the travel of laser pulses to measure the elevation of Earth's surface.

Medley: ICESat-2 only has a single instrument onboard, and it's it's laser altimeter. It actually splits that beam into six beams, which gives a much better spatial coverage with every orbit.

Boyd: Even though they do a lot of work from the air and space to study Earth, scientists like Brooke are on the ground, too. Studying our planet from the ground helps us get a hands-on perspective..

Medley: My job is actually fantastic, I love what I do, I get to explore Earth's ice both sitting at my desk solving problems, but also actually going out into the field and observing it. I kind of split my time making models and interpreting data, but also spending a lot of time whether in airplanes flying over the ice sheets…

Medley: Or also on the ground actually taking measurements.

Boyd: When you're studying ice, you're going to have to spend some time in some pretty cool places. And Brooke has had the opportunity to venture far out, where not a lot of people have been able to go.

Boyd: The deep field of Earth's coldest continent.

Medley: I've been to Antarctica three times, and it's my absolute favorite place on the planet. Antarctica is a very special place. You go and you fly into McMurdo, which is a station run by the National Science Foundation. It's kind of this little city of like 1000 people right on the coast.

Medley: When you go into the deep field, you take these itty bitty little planes. There's just five of us. They land. They never turn the engine off, because they want to make sure that they can fly away again, right. So you don't want a plane to get stuck there. It's this mad rush to get all your gear off the plane as quickly as possible. And then the plane takes off and there you are with five people standing in this flat white, nothing in every single direction. And it's like exhilarating and terrifying all at once.

Medley: So then the first thing you have to do is you know, make a fire so that you'll be safe. And then you start putting your tents up.

Medley: The one thing that I do remember the most about being there —it's just It's so quiet that you never, I'll never ever, you know, experience anything, where there's just no noise.

Medley: And I mean, there's no wildlife, there's no planes, there's no cars, there's no people, it's just you and…

Medley: You can almost hear your brain working. I mean, that's how quiet it is there.

Boyd: If you're a scientist and you want to know more about ice melt, sea level rise and climate change, Antarctica is a great place to be. It's nearly twice the size of Australia and holds over 90% of all the ice on Earth.

Boyd: And that ice can have far-reaching effects, not just on the height of the oceans… but on storm surges and flooding events.

Medley: I think the most important thing for people to understand is that sea level rise is predominantly coming from global ice mass loss, and that sometimes it might sound like a very small amount. A few millimeters here, an inch, a few inches there. And you might think, how is that really going to impact me? But I think we have to remind ourselves of the fact that it's that much more water. And when there's a storm, that means there's that much more water that can go further inland, it can generate more damage.

Medley: It's not about, Hey, your house is going to be underwater. Now, in some places, that will be the case. But it's more about, as soon as you put more water into the ocean, storms become that much more catastrophic and start damaging areas that weren't susceptible to floods before. So it just means that much more.

Boyd: With more water in our oceans… more people will experience the effects of climate change personally. Coastal communities are already dealing with the impacts of sea level rise.

Boyd: Places like Norfolk, Virginia are more prone to flooding. Areas along the oceans have seen more intense hurricanes.

Boyd: In order to prepare for these kinds of events, NASA scientists work on creating computer models of Earth's ecosystems.

Boyd: That way, they can run different scenarios of how these systems may react to climate change.

Boyd: Craig Rye is a research scientist, working to map out the unknowns of Antarctica, and help predict what will happen as it continues to melt. Like Brooke, he works on getting different perspectives on the Earth, but often from the comfort of his own home.

Craig Rye: My work is centered around trying to understand the Antarctic shelf sea in particular, and working on trying to improve our models of the Antarctic shelf sea. I spend most of my time in front of a computer trying to debug code.

Boyd: In 2020, scientists learned that Antarctica is melting around 6 times faster than it was only 30 years ago. Craig's de-bugged code will help us predict what could happen if that melting changes or continues at the same rate.

Rye: The system is very complex, maybe it's going to be quite difficult for us to produce really good simulations of it. So instead, why don't we try and take our best model of the climate. And what we'll do is we'll hit it with different scenarios.

Rye: One of the biggest issues in modeling Antarctica is that we don't have a really good idea of what's underneath it. It's an incredibly tricky problem, right? Like how do you develop a very high resolution, high quality map of something that's under tons and tons and tons of ice?

Boyd: For as much as we do know about Earth and its systems, there are still a lot of unknowns… especially about the future impacts of climate change.

Rye: A lot of this stuff can be a bit of a bummer, for lack of better words, right? It can at times be hard to find joyful narratives in the conversation around sea level. These are really, really important questions that I think could have an important impact on us all going forwards.

Rye: And they're also really, really exciting, cool science questions that involve really beautiful, sophisticated physics, interactions of lots of different types of physical systems on lots of different scales. And they involve cool tools like working with supercomputers and going on really exciting expeditions to polar regions. Walking up to the ice and poking it with instruments and doing really great fun work.

Rye: I'd just encourage anyone who's young and interested in physics to maybe take a look at this field and have a go at it. If you really want to do something that, I think, both really interesting and something really useful, polar science is a really, really great place to be.

Boyd: So much of the universe is still unknown. There are so many different corners still to uncover. And a lot of those questions come from our home planet.

Boyd: NASA is continuing to study our Earth with greater accuracy. The Sentinel-6 Michael Freilich satellite launched in November 2020. It aims to collect the most accurate data yet on sea level and how it changes over time. NASA's many Earth-observing missions will continue to help us learn more about our home.

Boyd: The Earth itself is a wild and wonderful place that changes every day. And whether it's from 300 miles above the surface, or a lonely tent in the Antarctic wilderness, our capacity for wonder and discovery never ends.

Boyd: This is NASA's Curious Universe. This episode was written and produced by Christina Dana. Our executive producer is Katie Atkinson. The Curious Universe team includes Maddie Arnold, Kate Steiner and Micheala Sosby, with support from Emma Edmund and Priya Mittal.

Boyd: Our theme song was composed by Matt Russo and Andrew Santaguida of SYSTEM Sounds.

Boyd: Special thanks to Ellen Gray, Ryland Heagy, Eric Land, Katy Mersmann, and the Earth Science News team.

Boyd: If you liked this episode, please let us know by leaving us a review, tweeting about the show @NASA, and sharing with a friend.

Boyd: Still curious about NASA? You can send us questions about this episode or a previous one and we'll try to track down the answers! You can email a voice recording or send a written note to Go to for more information.

Christian Dana: Wonderful, well anything else you think we should cover? Anything I've missed?

Schmidt: Oh, I could talk about this stuff for days. So don't ask me that. [Laughs]


Editor: Michael Bock

This article was originally prepared as a NASA Curious Universe podcast transcript.

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