From Sea to Changing Sea | The Role of Oceans in Climate || Radcliffe Institute

[MUSIC PLAYING] – This next panel is going to be talking about the role of the ocean in climates, as a climate driver, and how it’s affected by climates. Just on a personal note, after my trip to the Marshall Islands, I became obsessed with sea surface temperatures. So once a week, I would check the NOAA Sea Surface Temperature Anomaly Plot and post it onto Facebook, which earned a lot of funny comments from my friends. But to introduce the topic and to moderate, we have Amala Mahadevan, who was a Radcliffe Fellow for a number of years. She’s a senior scientist at the Woods Hole Oceanographic Institute. And she studies phytoplankton, but also an interesting twist. Phytoplankton and the hydrodynamics of the ocean. How upwellings and gyres and vortices can affect different organisms. So it’s an interesting combination of fluid dynamics and biology. So Amala.

[APPLAUSE] – So thank you, John. So in today’s panel, we’re very excited here to tell you a little bit about how the oceans shape our climate. And since the early history of the Earth, I would say the oceans really have defined the climate on this Earth. We have seen that the inception of life, the evolution of life happened on the ocean. But also, the oceans regulate the atmospheric carbon dioxide and oxygen. And the oceans contain, for that matter, a very large percentage of the Earth’s water, 97% of the Earth’s water is in the oceans. Just about 0.001% of the water is in the atmosphere, just to give you an idea. The oceans contain 98% of the carbon dioxide, in dissolved form, of course. So when we say that atmospheric carbon dioxide is going up or going down, you have to realize that there’s a lot in the oceans and the oceans have, in the past, regulated the atmospheric carbon dioxide very well. Whether they can do that in the future is something that we are still asking.

And the oceans– you know, if you think about heat, where is all the heat, most of the heat, 90% of the heat, is in the oceans. So in many ways, the oceans define the climate. The circulation of the oceans defines the climate. And about half the primary production on the Earth takes place in the oceans. And we see that the oceans are constantly in a state of motion. These ocean currents, they transport heat across the oceans. They transport salt. And in the very fundamental way, the oceans are different from the atmosphere. One is that they have enormous heat capacity. But the atmosphere is heated from below. And so the energy of the sun is what drives the atmosphere. Whereas the oceans, when you heat them by the sun, in fact, it’s stratifies the oceans, or it creates a density contrast, because warmer water doesn’t sink. So in fact, you see that the winds are what drive the ocean to a large extent. And mixing or overturning the oceans is, in fact, very difficult, because the sun warms the oceans.

So in a nutshell, that tells you that it’s difficult to communicate changes through the oceans. But the oceans really support a large part of our primary production on this planet. And so about half that primary production takes place in the oceans. And that organic matter, as we have seen in some of the previous talks, it sinks very gradually. Some of it get sequestered, that carbon to the oceans. So the big perturbation that we’ve made, that humankind has made, is that we have taken out that organic carbon that’s fossilized for millions and millions of years. We have very abruptly brought it out into the atmosphere. And we have created huge changes. And I have to say that the ocean has buffered, is buffering, a lot of that change that we might see because of those abrupt changes. A third of the CO2 that we put out in the atmosphere has gone into the oceans. And when we talk about global warming, and if you were to ask, where is all that heat that has to do with global warming, why is it that we don’t feel very warm today, it’s because 90% of that heat is in the oceans.

So I’m really excited today to have this panel here. We have here three oceanographers whom I really admire, whose work I really admire. Maureen Raymo from the Lamont-Doherty Earth Observatory at Columbia. And she has worked on the past climate of the Earth. And her work has shown how important it is to think about past climates, and how past climates help us understand the changes that we’re going to go through now, or we’re going through at present. That’s because we have a very short observational window in these last few decades. And so understanding past climate is really important. And then we have Rebecca Woodgate, who is an arctic oceanographer. And she’s done a lot of observations in the Arctic.

And she’s really pushed our understanding of how sea ice and the oceans interact. And the big changes that are occurring in the Arctic, it’s one of the most vulnerable regions in the oceans because of the sea ice and the interaction with the oceans. And then we have Lynne Talley, who has been instrumental in understanding the large scale distribution of temperature, salt, and the global circulation of the oceans. How these things get conveyed and transported across the oceans, what are the changes? And she’s been instrumental in some of the very big ocean observing programs that have global and international programs. And her understanding of the global oceans through those programs has really changed a lot of our understanding as oceanographers.

So it gives me enormous pleasure to have these three people here today. I don’t want you to go away thinking that oceanographers are necessarily women, but some of the best oceanographers are. [LAUGHTER AND APPLAUSE] – Well, thank you, Amala. And thank you for inviting me to speak here. I’m very happy to be here. So let me just get right into it. Hopefully, you’ve had time to get the joke. I should also say that video of the ocean swirling is one of my favorite videos in the whole world. It’s called perpetual ocean if you want to pull it up and watch the whole world. OK. So I’ve spent most of my career studying past climate change. And most of the last five to 10 years studying sea level as it relates to the past history of the polar ice sheets. And today, there’s two major polar ice sheets. There’s the one in Greenland, which if you, hypothetically, could melt it all and spread it in a single layer over the ocean, sea level would rise by about six meters or 20 feet.

And then in the South Pole, there’s the West Antarctic ice sheet over here, which again, is about the same size as the Greenland ice sheet. And then the much larger East Antarctic ice sheet, which you have to go back 40 million years to find a time when that whole ice sheet had melted. And at that time, sea level was about 180 feet higher than today. So the question I’ll just pose here is, how sensitive are these ice sheets to a modest global warming? And by modest, I mean, let’s say one degree Celsius warmer than today. I actually know a little bit about a time period that is widely agreed to have been two to three degrees warmer than pre-industrial, which would be one to two degrees warmer than today. And at that time, geochemists, using various methods, have reconstructed atmospheric CO2. It is about 400 PPM, which I know at least some of the people in the room I recognize know that’s exactly what it is today. It’s about 401 this week, PPM. It should be 280 PPM, but we’ll come back to that. And what I’m showing here is a site on the north coast of Ellesmere Island, and an artist’s reconstruction based on the fossils, and plants, and animals, and pollen that have been taken out of that dig show a reconstruction of what the north coast of Greenland and Canada looked like three million years ago.

The Greenland ice sheet did not exist. OK. So climate is changing all the time. Even more recently, there’s been a profound change in climate. This is 21,000 years ago, very recently. And obviously, the Greenland ice sheet has jumped the Davis Strait and has expanded dramatically down over North America and Fennoscandia. I don’t know if this is a big Game of Thrones crowd in here, but if the people that like it will appreciate this quote. So that is the height of the ice sheet over Boston at the peak of the last ice age. OK. So that was just a blink of time ago, obviously. So why do these changes happen? The climate system is infinitely complicated. And there’s no scientist on our planet that can be an expert in every part of the climate system. But at the same time, it’s somewhat very simple. And you can go to the radiation chapter in a freshman physics book and see a very simple equation to calculate the effect of temperature of the Earth.

We don’t need that, but all you need to know is it’s very simple. And the surface temperature of the Earth just adds one more variable, which is the concentration of greenhouse gases. And so I like to think about it when I talk to general audiences, just say, look, the Earth’s climate, the temperature of the Earth– we’re a ball of rock. We get heated by this star that’s a distance away– which I don’t know– one light year? I don’t know. And there’s three variables that control the Earth’s temperature. How close we are to the sun– and that actually varies subtly through time because our orbit isn’t perfectly circular, and other large planets perturb our orbit, like Jupiter and Saturn, on time scales of tens to hundreds of thousands of years in very predictable ways that can be calculated. And sometimes, over billions of years, the solar output of the sun can change. But on human time scales, it’s essentially constant, which is why we call it solar constant.

So that’s one big knob you can change that can control Earth’s temperature. The other is the Earth’s albedo or reflectivity. If you expand the snow and ice coverage at high latitudes, you make the Earth more reflective. And so more of the solar radiation is just lost to space. It’s reflected to space. It’s not available for heating. I’m sure we’ll hear a lot more about that in the Arctic talk. And then, finally, we have this thing called greenhouse gases. And so we have all this heat coming in from the sun. It’s warming the Earth’s surface. The Earth’s surface is cooler than the sun, so it re-radiates outward at longer wavelengths. And it just happens to interfere with the molecular structure of certain gases, especially CO2, which can prevent it from escaping. And then re-radiates it back to the surface. So just like throwing more blankets on on a cold winter night. So these are the three knobs. And everything I know about every climate change that has happened in the past– and this I will show you– can be explained by just changing these three variables.

And I’m going to show you a model. This is the climate model with an ice sheet embedded in it. And it’s the last 400,000 years. This is a sea level scale. And this is what the climate for the last 400 years has looked like, just the only variables being our variable orbit around the sun, changes in the Earth’s precession and tilt of the Earth’s axis, and the CO2 changes that we know occurred from ice cores. And it actually– this is a model result, but it looks remarkably like what we know climate did. Want to see that again? – Yeah. – I could watch it all day. This is a paper we published in Nature by Ayako Abe-Ouchi, who is actually the only female scientist I’ve ever met in my field from Japan. So one of the things you may notice is that ice sheets grow much slower than they melt.

It’s very easy to melt an ice sheet quickly. And the reason is because, as you see, as it starts to retreat, the ice sheet has depressed the land under it. And so the ocean can flow in very quickly and destroy that ice sheet from below as well as from above. So ice sheets can melt very quickly because they can become unstable and warm ocean can flow under them. How quickly? This is data– well, this is the results of a study of Tahiti in the Western Pacific. And what the scientists did was they went offshore and they drilled down. And they can, with very precise dating and drilling, determine the depth below sea level of the coral as it tracked the sea level rise at the end of the last ice age. So as the ice sheets are melting quickly, the seas are rising, the coral is keeping up. It can do that. And they were able to determine that as the last ice sheet deglaciated, sea level was rising at rates of 40 millimeters per year, or 12 feet per century.

So keep that number in your mind as we move forward here. Right now, sea level’s rising to three millimeters per century– sorry, per year. Did I say century? I meant year. Three millimeters per year. But how high was sea level during some of these little periods in the past that were just slightly warmer than today? This is a question that’s very easy to answer and also very difficult to answer. It’s very easy because the evidence for higher sea levels during the recent past is all around you. This is me standing with my postdoc, Nick [? O’Leary ?]. This is the modern Ningaloo reef system in Northwest Australia. We are standing on a stranded fossilized reef that is probably about 400,000 years old from a time period that was slightly warmer than today. This is a reef. This is the fossilized coral. This is my student Mike Sandstrom from the Cape ranges of Western Australia. That’s from the last interglacial warm period, 125,000 years ago.

It’s a few meters above present day sea level. This is from a three million year old deposit in Pliocene, the Pliocene warm period in Africa. No coral, but we have fossil oysters with fossil barnacles still on the fossil oysters. I mean, ooh, you’re at sea level. But why is it difficult? We see this evidence for high sea levels everywhere. The major reason it’s difficult is because the ocean– unfortunately, the ocean basin is not like this tub. And you can’t just look at these as like bathtub rings from the past. The continents, the crust of the sea floor, and the land, they’re constantly in motion. They’re being loaded and unloaded by ice sheets, by water. It’s constantly moving. So it’s quite a challenging problem. And there’s a fantastic group here at Harvard led by Jerry Mitrovica that’s been working on this. And many clever scientists around the room have made huge progress in unraveling these challenges over the last five to 10 years. So I’ll jump right to a summary slide, which is in a paper we published in Science last year. And so here’s– and this is kind of a complicated slide, but it’s really cool too. So here’s a CO2 scale.

There’s pre-industrial CO2. Here’s present day CO2. And here’s a sea level scale. And here’s today’s ice volume. One degree warmer than pre-industrial right now. Here’s 125,000 years ago. The CO2 was the same during that warm period, but we were just so slightly closer to the sun, it was warmer. It was about one degree warmer. A smidge because of the precession of the Earth varied. And all these different studies as to– the estimate of all these different studies is that sea level is six to nine meters higher than today. OK? And this is a window of time that’s 10,000 years long. 400,000 years ago, it was a little bit warmer, six to 13 meters best estimate. And then in the Pliocene, it’s been so long, the continents have moved so much, we have a very hard time. Huge error bars. We don’t really know. But two to three degrees warmer, higher CO2, 400, same as today. And I wish I could tell you more exactly what sea level was at that time. I can’t. OK.

So you know, this is 6 meters, 20 feet. Let’s take it back to just four feet, which is completely within the realm of what could happen by the end of this century. I’m perfectly comfortable with this as a prediction. And I’m sure there are others that are as well. So four feet above present. Five million people live within four feet of sea level in the US today. It’s a huge amount in Florida, obviously. And in terms of our national infrastructure, energy facilities, ports, Naval bases, there’s a huge amount of real estate that is in this zone of risk. Obviously, sea level rise is not just a problem of the United States. It’s a global problem. And we may be hearing more about the Marshall Islands later too. Does anyone recognize this capital city? It’s Mali. It’s the capital of the Maldives. And so you have over 300,000 people living on an island that’s a meter and a half above sea level. And this is just one of like thousands and thousands of inhabited islands around the world.

And when you hear the expression climate refugees, this is what– these are people just like us that you’re hearing about. OK? So I’m going to basically leave two more possibly depressing thoughts about sea level rise. And that is, first of all, I think a lot of people have this vague idea they’ll be able to deal with it, like keep it back. I don’t believe that’s very realistic, just based on my observations of various places I love. And the other thing that’s really important, I think, for people to come to grips with and tell themselves is that sea level rise is irreversible on the time scale of centuries. You could probably cool the Earth’s atmosphere easier than you can regrow an ice sheet. So every year, the increment of water that’s going in from the melting of polar ice sheets and the thermal expansion of sea water, that’s an increment of sea level rise that there, and that we’re going to have to deal with for centuries to come. So to wrap that up, what I know for sure, climate is changing naturally all the time. Small variations, very small variations in incoming solar radiation, albedo, reflectivity, and greenhouse gas concentrations can lead to large and sometimes rapid changes. The activities of seven billion people are capable of causing effects of this magnitude.

And here is the CO2, carbon dioxide, record of the last 10,000 years. The Holocene, the warm window of time within which human culture, agriculture flourished. It was about 270 parts per million. A subtle rise starts about 5,000 years ago. Many scientists believe this is due to early agricultural and deforestation. And then here, this interval right here, blown up right here, here’s the 18th century, the beginning of the Industrial Revolution. And this rise is the addition of CO2 to the atmosphere from the combustion of fossil fuels. And obviously, this is out of date. We’re already over 400 PPM. I have another video here. There it is. So this is what that CO2 has done in a very nice visual. We humans have cranked the knob. They’ve taken the CO2 dial and they’ve turned it hard to the right, very hard.

This is a surface temperature anomaly map based on instrumental data from around the world. Want to see that one again? – Yeah. – Yeah? It’s cool. So what you’re looking at is the mean is defined as 1951 to 1980. And so what you’re looking at is every surface anomaly relative to that mean. So the beginning is generally lower than the mean. And as you see, when you get towards the end, you’re generally hotter than the mean. In partnership with that warming atmosphere, heat penetrating the ice sheets, heat penetrating the ocean, causing thermal expansion of the oceans and melting of the ice sheets, sea level has been rising. These are various different studies based on different techniques, including tide gauges. And they’re in more disagreement the further back in time you go.

But I think what everybody is in agreement about is that sea level is rising and the rate is accelerating. This is from a post-doc at Harvard, Carling [INAUDIBLE]. And just to take this time window, 1900 to 2000, and put it on a time scale of the last 2,000 years– right? It’s all about perspective, right? Here’s that same curve. You would put it right here. So natural variability, the rise in sea level due to two human-induced global warming. So what is the– I’ll just wrap up here. One more slide. What is the atmospheric CO2 and sea level likely to do over the coming century? And of course, it’s not just the next 100 years. It’s many hundreds of years into the future. This is not a scientific question that scientists can answer. This is a question that’s going to be completely dependent on the individual and collective actions of citizens and their governments. But I will say that if you look at this, here is our current CO2 emission rates. And what this is showing is these are the paths that, as a planet, we have to choose to be on. Can we turn around global CO2 emission rates quickly or is it going to take longer? And the point to make here is even if you turned it around today, you’re still putting CO2 into the atmosphere.

Much of it’s going into the ocean, but most of it stays in the atmosphere. And it will stay there for hundreds of years. So even if you turned it around today, you’re committing yourself to CO2 levels up around 500 parts per million. Every decade you put it off, you commit yourself to higher and higher sea levels down the road. So as someone who knows what these changes in CO2 have done in the past, this would be of great concern. OK. So I’ll just thank you for listening. And happy to take questions later. [APPLAUSE] – Well, good morning. I’m Rebecca Woodgate from the University of Washington, Seattle. And for the next 20 minutes, I would like to take you up to the top of the world, peer into the Arctic, like this polar bear is appearing into her Arctic. In her case, she sees a submarine come at her. Something she doesn’t understand, probably.

There’s things about the Arctic we do and do not understand. This word here, Uggianaqtuq– it’s an Inuit word. It means “a friend acting strangely.” And that’s how the Inuit, who have lived in the Arctic now for around 10,000 years, how they now view the Arctic. A system that they know and love, which is behaving in ways they cannot understand. Where is the Arctic? It falls off a lot of maps. Here it is at the top of these maps. It turns up squashed into a little layer at the top. But if you take a globe and you peer down from the top of it, you can see there’s a proper ocean up there. You can twist this map round because it is usual when you’re talking about the Arctic to put the country you’re talking in at the bottom. Lots of countries here.

Lots of countries vying for owning the Arctic. This picture– anyone know this picture? This is the Russians putting their flag at the North Pole, three miles down under the ocean, in 2007, saying it’s theirs. We’re not going to go there today, but there’s interesting debates about that. Give you an idea of scale, this is relative to something I hope you recognize. It’s bigger than the US. If you want some numbers, here’s some numbers on it. It’s the smallest of the world’s five major oceans. But it’s famous in many, many ways, even before the changes of recent days, for frozen ships, for passageways, for the hunt for the North Pole, et cetera. Perhaps of the most poignant is the Northwest Passage, which is this route between the Atlantic Ocean, which is down here, and the Arctic. The search for the Northwest Passage.

And let’s start there. Let’s start with some recent Arctic ships. Can anyone tell me what this is? This is the wreck of the HMS Terror. This was a ship which set sail from England in 1850, 1845, looking for the Northwest Passage. The Franklin Expedition, the lost Franklin Expedition. It’s not a happy story. They overwintered three years in the archipelago trying to find a way through. After more than one and a half years struck in the ice, they left the ship trying to walk South and none of them survived. And since then, we’ve been looking for those ships. We found those ships in the last year. I say we– this is Parks Canada. The Canadians put a lot of effort into doing this. This is the ship on happier days. Some years before this, 1836, getting stuck in the sea ice was an occupational hazard of being an Arctic explorer in those days. So another ship in the news this summer. Anyone know this one? This is the Crystal Serenity, a luxury cruise liner, 1,000 passengers, 700 crew, which had just gone through the same fabled Northwest Passage in three weeks, stopping in villages which have a population less than a third of the number of people on the ship.

Contrast these, the Franklin’s Expedition. Here they are. This is as far as they got. This is where, basically, the whole crew perished. Nobody came home. And the Crystal Serenity, which has gone through in a nice planned trip for three weeks, come out in New York. What’s the difference? The difference between this is ice. Let’s talk about ice. So if I take sea water and freeze it, I start to get very little crystals. They float up to the surface of the ocean. They form a kind of an oily layer on the top of the ocean, which gradually pushes together to form a sheet of ice. OK. This has some resilience. I wouldn’t walk on this at this stage, but it will push together and you can see the edges. You can see here the striations of the layers push against each other. Let it go a bit further and these layers form into more sheets.

If you’re a penguin, you can walk on this. No, there are no penguins in the Arctic. As these sheets come together, we call this pancake ice. People at sea will think of a lot of things. And they get thicker and come together over a period a few more days to make into ice floes. Ice floes can be several yards to a mile to several miles across. I don’t know how you got here, but this gives you an idea of scale. This is the first time that I would walk on this stuff. This is about one to two meters thick. So here to here thick. This is first year ice, will form over season. Here’s a ship plowing through the ice. As it goes through, it pushes the ice up on edge so you can see how thick the ice is from here to here. This is not how we get the thickest ice in the Arctic. If you just let it grow over more than one year, it would grow to three meters, not quite reach that.

Nine feet tall. But what makes it really thick is as those pieces of ice, those floes of ice push together, they ridge, just like a mountain range will ridge. And this is what makes our thickest pieces of ice. I’ve put here a picture from one of the pretty buildings from my university. 90 feet tall is this tower. And that is a not atypical height for a ridge that you’d get in the Arctic. Just like an iceberg, there’s more below than above. So if we have this chap standing here beside the ice, and we measure how far above the water he would be and how far below the keel, you’re looking about an ice keel about the height of that building. So these are common sizes of thicknesses of ice in the Arctic. Now, while this is pushing together here, it’s coming apart somewhere else.

And this gives us what is called leads in the ice, cracks in the ice which can appear overnight. Very, very quickly. Sometimes in inconvenient places. This is a current hazard of Arctic exploration, as you might get a lead come through your camp in the middle of the night, with interesting consequences. Didn’t fall in, we don’t really mind. I prefer to work off ships for that reason. And you can see some ships here. Here the ship is giving the scale of the ice floes. As the summer carries on, the sun melts, the snow on the top of the ice gives you melt ponds in the top of the ice, which will eventually decay the ice away. It is a habitat for life, is ice. We have our charismatic megafauna. And we have our, perhaps, not so charismatic tiny fauna. This little brown striations you see here, that’s not mud and that’s not paint off the ship. That is actually little microbial community plankton which are growing in the channels of ice. You can do this yourself. Go home, take some salty water, chuck it in the freezer.

And tomorrow morning, put drops of food coloring in it and you can see the channels that go through the sea ice which are channels for life. It’s also home for people. The Inuit have made their history in the Arctic for 10,000 years. And to them, ice is not a hindrance. Ice is their way of getting around. Ice is their highway. So where are we today? This is almost today’s sea ice there. This is a satellite image. Greenland’s here. The colors give you the ice concentration. These dark areas are water. You can see the sea ice now building up from it’s expanding as the winter has started in the North, expanding back out to the coasts and down into the lower latitudes. That’s a snapshot of today. It’s a large seasonal cycle in the sea ice. This again, satellite data. We’re over here, again, now showing the maximum extent in winter and the minimum extent in summer. Occur March and September respectively. Large seasonal change, of course, because the sun comes up and melts the ice. Well, how does this year compare with the past? We have this satellite data back to 1979. And I pulled out the years which have the maximums in the seasons and the minimums in the seasons. And to make it a bit easier to see, I’m going to change it now to sea ice extent.

And this pink line in both of these maps shows the monthly median edge from ’81 to 2010. So what we thought was standard for most of our satellite record. So in the winters, you know, we’re kind of close to that. Getting a few changes. But the summers, we’re seeing this very dramatic loss of sea ice. Let’s put those on time scales. Here we have the whole time series we have, and the trend line through that. And it’s not very much. It’s a few percent per decade. This is the winter. But in the summer, we’re getting a very much greater change, 13% per decade. OK. That’s we’re losing– 13% of the ice per decade we’re losing in the Arctic. To look at where we’re losing it, in the winter, we’re losing it around the edges. In the summer, we’re losing it in the middle. We’ll come back to these patterns in a moment. So we’re losing ice area? Oh, yeah.

The area that we’ve lost so far is about a third of the area of the US. And we’ve probably lost about 50% of the old summer sea ice extent, from about the 1980s. It’s not just that that we’ve lost. We’ve also thinned the ice. So it’s harder to put this together. We put together from submarines and satellite images. But this gives you an idea, in the 1980s– this is winter and summer– we had about three meters of ice. And now, in more recent era, we’re down to about half that. This satellite picture’s showing you how that’s distributed. There’s lots of statistics that have to go into this. But this is confirmed by everybody who goes up there, the people who live there, who talk about– saying we no longer get the strong, thick ice we used to have. We only have feeble, weak, young ice.

So you can say sea ice is thin from very roughly about 50%. Put that together, we’ve lost extent, we’ve thinned. We end up with a loss of volume. This is our best estimate to try and put that all together, which is a model, and which says we have lost basically 30%. No, we’ve not lost 30%, we only have 30% left of the summer ice that used to have. OK? Some people will say this is a quarter, but it’s around that magnitude. So there’s a huge change we’ve seen in the Arctic in the last decades. How did we get here? Polar bear. We’re always going to have a polar bear. How did he get there either? So we got there in many ways. Things that we understand and things that we don’t. We understand now how well the ice moves. So if we put a pole in the ice at the North Pole, the floe drifts around and the ice moves with it.

To be more useful in that, we can put in a set of instruments which will tell you their position. So dates rolling in the corner here. White is the satellite sea ice extent going from the summer to the winter to the summer to the winter. And the little red dots are buoys that have been put on the ice and register their position. You see they go around in a kind of circle around here. Some of them run down the edge of Greenland like this. This is how the sea ice is moving. They’re just sat on the sea ice. They jiggle around together because the wind is forcing them. And we can see this pattern of a circulation there, and then ice coming around here and coming out down this way. And as we come to the 2000s, we see the summer extent getting less every year. And we can see this melting back to this incredible ice melt in 2007, which really was something that nobody expected or saw coming.

So from that data, we can go on and say, well, we can see how this is moving. We can tell how old the ice is. And this is a similar movie where the colors are now the age of the ice. So white is now greater than 10 years, and these bluer colors are more recent, younger ice than that. It’s the same buoys as you saw before. We’re seeing here in the 1980s, most of the Arctic was covered by old ice. But changes in the wind have changed that. We’ve taken all this area of ice, then managed to flush it out down here through to the Atlantic Ocean. And over this time period, we’re losing the older ice in the Arctic and coming back to just having a very much younger, newer ice in the Arctic Ocean. We’ve flushed the old stuff all away. To see the before and after, if you like, here is the before. Lots of old ice.

And here is the new with very little ice left. In doing that, we’ve flushed away the old, thick, resilient ice. It now moves faster and it’s thinner. The other thing that goes with that is that it can also melt easier. If we look at how things have changed, is it just due to this motion? No, it’s not. This is a movie of 2000, again looking at ice and clouds now. So here’s Greenland again. And you see here the coast of Alaska around these points. The big things that swell past are clouds. But mostly, what you see underneath, this is the ice moving. Sometimes the wind blows. You’ll see black open up here. That’s open water opening up along the coast you see here. You see– if you watch this bit, you can kind of sense the motion, which is the same motion we saw before. You see these massive cracks coming across the whole of the Arctic. Those are the leads that we talked about as the ice pulls apart driven by winds and currents. In summer here, the ice starts to pull back from the coast.

And you can see here the retreat of the edge, which is faster than the speed of the ice. Basically, as we watch those through August and through September, that ice just entirely melts away. OK. So what causes it to melt? The main thing is this idea of an ice albedo feedback. This is the reflectivity that was talked about a second ago. Quite simply, the ice is shiny and the water is not. So if sunlight beats on the ice, it reflects that heat back to space. If it beats on open water, that heat is absorbed and we get a feedback. Let’s say we start with more ocean water. That water can absorb more heat. That means it will get warmer, which means it will melt some more ice, which means we have more open water, which means we go round and round this circle. It’s a vicious circle. A vicious circle of demise of sea ice. The technical physical term for that is a positive feedback. And so once we can set this off, the only thing that’s going to stop this is by turning off the light. Winter coming is the only thing that will stop this feedback. But we have to set this off.

And to set this off, what can we do? We can blow the wind off the coast. But there’s a further role which is bringing heat into the Arctic, and that is the oceans. This is now a map of the bathymetry of the Arctic Ocean. Deep bits of blue about the size of our local volcano in Seattle. The shallow red bits are more shallow. And there’s other things there that give you some idea of scales. We have an entrance here to the Atlantic Ocean, an entrance here to the Pacific. And waters flow from both of those oceans into the Arctic. Here’s the Atlantic water which comes in, the deep current. And it likes to put its hand on the right hand wall like a good current should in the Northern hemisphere, because the Earth is spinning. And it goes around following slopes and ridges. It goes around very slowly, a few centimeters per second.

So it’ll take eight hours to go one mile. So if we send some water in here, depending whether it takes the short route back through here or the longer loops back through here, it can take 10, 20, or 30 years to get back out again. So we send a heat signal into the Arctic, that the time it’s going to go around and then come back. On the other side, the water comes from the Pacific. That’s higher up in the water column. It’s also a lot fresher. It tends to stay with the top of the ocean. And it’s more driven by the ice and by the winds. It moves a lot faster. It actually covers about half of the Arctic Ocean here, then comes out through the Canadian archipelago. So it will only take about 10 years to cross the Arctic. What both these currents have in common is they bring in heat to the Arctic Ocean. Here’s some pictures off the Fram Strait, seeing the heat from the ocean coming up and melting the ice. If we look at that Atlantic layer, [INAUDIBLE] that we had for that, and we look at the ice edge, we can see here these tongues of hot water coming across Greenland and the Bering Sea here, melting back the ice edge. Very suggestive from the patterns that the oceans are bringing in the heat, which is melting off the ice. And I show you that as a pattern, that we can do the maths.

We’ve had measurements in these channels at great expense for many years. We can see that over these decades, the temperature of the waters have warmed as we go through the channel there. And you can do the maths, so you can work it out. But we’re just about right for the numbers, the amount of winter ice that we’re losing in this area, which is 10% per decade in this particular area, is likely caused by an ocean warming of 0.3% per decade. It corresponds to that map we had of where we saw the ice going away in winter. We flip over to the other side of the Arctic, the Pacific, here the water’s coming in and only warm in the summer. But we see the same pattern. We have here the same, the tongues of water, again driven by the topography, melt back tongues in the ice. And this is now. We’ve got the sun up here.

We can set this off. And now the ice albedo feedback can take over and melt back the ice. The other thing that this water does, it ends up deeper in the Arctic Ocean and it can add to the gradual thinning to the ice that is there. Yet another nail in the coffin of the poor Arctic sea ice. Again, we’ve had measurements here for many years. We can see this heat flow increasing. And we can do the maths, and we can say, this is the effect of these heat flows. We’ve got warmer waters coming in from both sides. So what is our causes of recent sea ice retreat? The increased heat from the Pacific, increased heat from the Atlantic. Warmer atmospheres I haven’t talked about, but that’s coming into this too. Added on to a preconditioning, where we have flushed this older ice out of the Arctic. So all of these things are conspiring to give the Arctic a really bad day. Right? We’ve all had bad days like this. This is the Arctic’s bad day. Quite how these interplays, things that we still have to put together.

We have so far not managed to predict any of these extreme ice melt years that we have had. So what sort of a hole are we in? This guy– this is how we used to do Arctic oceanography. This is one of our technicians who has chiseled his way down through a bit of sea ice. OK, this is a good bit of sea ice. Chiseling down so he can get to the ocean below. OK? Digging himself a hole. The ice albedo feedback is kind of a killer in all of this. It comes with the idea of polar amplification. We saw that in an earlier video, though you may not have been looking for it. The poles are going to warm first, especially the Arctic, because we are losing the albedo. We’re losing the shininess of the Earth, and we’re allowing all that energy to absorb into the ocean. Quite how that is going to play out as we push those Arctic waters into the rest of the world, we haven’t quite worked out. That’s more Lynne’s field than mine. What also comes with this is a change in the atmospheric circulation. There is a cap of cold air which sits over the Arctic which basically can get extra wobbles on it.

And those wobbles are thought to be driven by changes in the sea ice extent. And that gives us the cold air outbreaks and the dumping of snow onto the East Coast that we’ve seen in recent years. This is how the Arctic extends its fingers down into mid-latitude weather. There is also the impact in the Arctic of where the warming that we’re having, permafrost thawing, loss of ice protection from erosion. If the ice pulls back earlier, the storms can affect things more. And we have whole villages falling into the sea. Loss of infrastructure in terms of roads, buildings that are built on permafrost. Also within the permafrost, we have a large store of methane hydrates. These are frozen methane under the sea. Currently stable, but as we warm, we could release that with potentially huge consequences. We don’t quite know how that one will play out either.

We also have with this the opportunities which are coming from this– exploitation of resources and Arctic shipping, which can now talk about going across the pole. And in all of this too, we think about the peoples and the governments. There are people who live up there, who this is their way of life. And there are the governments of the world who are clamoring to own that piece of the ocean. So what have we seen in our trip around the Arctic? We’ve changed the seasonal ice extent, how it changes. How we’ve thinned the ice. If you take just that one number, take away this. We’re only left with 30% of the ice that we used to have in the summer just a few decades ago. We’ve looked at why that things might be causing that. And we’ve looked at the possible implications of all of this. It’s a field which, because of the ramifications, these broad ramifications, and the way the thing interacts, we really need not just an interdisciplinary, but also a cross-cultural approach to have a responsible and coherent way of going forward into the future. Thank you.

[APPLAUSE] – OK. Now for some more good news. [LAUGHTER] Here we go. Well, I live in– I’m from Scripps. This is what it looks like every day. So up here, I have to put on a jacket. I thought I would go ahead and put my cartoon, my favorite one out in front, because we’ve lived in kind of a politicized environment the last two years as climate scientists. And I think it’s ameliorating a little bit. We’re going back to some sanity. But this is one I’ve had in there a long time. And I’m going to talk a bit about how we get from oceans to drought, or what we can learn about the water cycle of the planet from what we measure in the ocean. And I actually have a very brief set of definitions, because we have– actually, speaking from a place of– I’m going to show a lot of results from the Intergovernmental Panel on Climate Change, IPCC.

I had the great privilege to be part of it the last two reports we put together the first time. It had an oceans chapter two times ago. And we continued that with this one. So I’m going to show a lot of stuff from a particular slant in the IPCC of how the oceans are changing and how they contribute to climate change. But first, you want to know what we’re talking about. So there’s climate. And there’s climate variability. We have a lot of that. And there’s El Nino. Some years are stormy, some years are not, et cetera. That’s natural. And we have major natural climate variability on the planet. And that can be affected by climate change, which is what we drive through anthropogenic forcing. And so we’re seeing all kinds of records now. So I just want to get those two definitions in place. It’s kind of, well, [INAUDIBLE] such that we have a framework there. These are four major overarching conclusions from the IPCC. This is not the oceans part.

This is the whole thing. Number one, which Susan Solomon put forward in the 2007 IPCC as the head of the working Group 1, warming of the climate system is unequivocal. We came home from that with buttons to wear. Warming is unequivocal. Global warming does not cause ice ages. That was the second part of that. Number two, human influence on the climate is clear. Number three, continued greenhouse gas emissions will cause further warming. And number four, limiting climate change requires substantial sustained reductions of emissions. So let’s look at the Earth. Is it warming? We’ve already seen this in video. This is the trend since 1901 up through 2012. Where it’s white is where there’s not enough data. Mostly it’s warming. There it is. And it’s mostly warming over land, but it’s warming over the sea, and that’s important. This is from this wonderful NASA website, climate.

nasa.gov. Go on there if you want to put something on your Facebook page there every day from there. It’s great. There is our graph. And when you go online, actually, that red dot at the end animates. Boom, boom, boom. It’s the hottest ever measured with direct records this past year. And this year, 2016, was higher. So there we are. We’re getting warmer. And they give you a nice number for how much warmer we are. It’s almost one degree warmer. It’s projected to get warmer. And there’s– the IPCC has different ways of going about that with business as usual, or some reductions, or whatever. So you get from moderate to extreme. The one on the left is– the right, your right, is obviously more extreme. But that’s where we’re going if you just burn it all. And you see the polar amplification that Maureen and Rebecca were talking about due to the ice changes in the North. And you see the ocean in the South is not doing a lot.

There’s a lot of ocean down there. Water has a lot of heat capacity. What’s creating climate change? Greenhouse gases mainly. This is the big elephant in the room. And they are the dominant cause of observed warming. There’s other ways– very complicated subject, but this is the big part of it. And the largest contribution is CO2. And this is the Keeling curve last night, 401. We’re actually at the low for the year because we’re at the end of the northern hemisphere summer. This is measured at the top of Mauna Loa. Dave Keeling set this up in the International Geophysical Year, 1957. And with dogged persistence, kept it going. And now it’s recognized as our really amazing record. You see the planet breathing, and the summertime and wintertime, summertime and wintertime. And relentlessly going up.

And that’s the tail at the end of the curve that Maureen showed. What happens with the greenhouse gases? We get lots of stuff happening, bad stuff. Well, different stuff. It depends on whether it’s good or bad. Warming– atmosphere and ocean. We melt the ice. We melt the ice sheets. We raise sea level. We do change the hydrological cycle. We’re going to change the patterns of drought and floods. Not the patterns, but the strength of drought and floods. We have more extreme events. You can’t attribute any given storm to global warming, but you can attribute years of changes in extreme events. Ocean acidification is another important one for the ocean. So looking at the ocean, how does the ocean participate in each of these parts of it? In carbon– just one or two slides– heat, and ice, just a little bit, sea level rise, and the water cycle.

So a statement from the IPCC– the ocean has absorbed about 30% of the emitted anthropogenic carbon dioxide. OK, that’s an important number. You put a certain amount of carbon up in the– you burn it. It’s coming from fossil– it’s fossil fuel burning. 8% land, 92% percent fossil fuel. Fossil fuel burning into the atmosphere. A third stays up there, a third goes into fertilizing the land, and a third goes into the ocean. And the ocean is not going to sit there and soak up the next 40%, 50%, 60%. This is an equilibrated sort of system. And once it’s there, it’s there. Maureen showed a nice graph showing that we’re in a commitment phase. You put the CO2 in the atmosphere. It’s not going anywhere. A third goes into the ocean of the part that goes up. How do you get it out? Well, you have to stop burning it to keep it flat. And then maybe you need to start removing it. Here’s the other CO2 problem. The ocean is 70% of the Earth’s surface. That CO2, 30% that goes into the ocean, it’s not a garbage dump that you just put in the backyard.

It goes in and it affects the marine life. So you get acidification. Carbonic acid is formed when you dissolve CO2 into water. A little bit changes the pH. And that excess acid has important impacts on organisms. And there’s a pteropod. They’re kind of in danger. They have beautiful movies of them– I didn’t bring any animations– flittering around. The poor pteropods. Anyway, coral reefs, et cetera, you may read about all these things. And this is going on now. And so there are projections of how the surface pH will change in the ocean, and also how the undersaturation, how much acidification is impacting the organisms. That’s it for carbon. That’s an important second part of the carbon problem, if you haven’t been kind of cued into it before though, that the oceans are affected by the extra carbon as well. Now we go to heat. OK. So you’ve heard this number already, that the excess energy in the system due to anthropogenic forcing. So this is the excess. Not just the heat, but the excess is more than 90% of what’s in there. So yay, the ocean is really helping us out. If that were in the atmosphere, think of how warm we would be.

And I’ll show a graph. How do we know these things? So this is where we get to what I do. We go out to sea and make measurements. How do we know where the heat is? We measure it. This is the latest– yesterday’s, maybe today, yesterday– map of where we have had ocean temperature and salinity profiles over the last month. So we have a global network now. It’s been a phenomenal community, international effort. Technology was invented at Scripps by Russ Davis. Dean Roemmich at Scripps has been instrumental in taking this to the world. Taking the instruments to the world. This is our network for the ocean. It’s the upper 2,000 meters of the ocean. That is a picture of a float that we were putting out off of a ship in the Indian Ocean last year. Here’s what you get from it. Is the ocean temperature changing? Yeah, it is. This is the change in heat content in the upper part of the ocean– 700 meters times three, 2,000 feet– since 1950. Mostly red.

Oh, OK. And then there’s a lot of really interesting structure to it that we could spend days and months discussing. But it’s mostly red. It’s pretty patchy, because we’re using measurements since 1950. So it’s ship measurements in addition to these floats. And then– I’m in the middle of that one– we go out to sea and we measure to get the rest of the ocean to the bottom, to see how it’s changing over the decades. And we make extremely accurate measurements. And here’s a map from Sarah Purkey and Greg Johnson. How to make your thesis become a classic– you get 10,000 citations. This is the map. This is using our very precise– very accurate– not precise but very accurate deep measurements to look at where the warming is happening below 4,000 meters. And you see it’s a very different pattern. This is a big eye opener. It’s very much in the South. And this is where a deep water forms around Antarctica and goes to the bottom. And the balance is changing.

And essentially, the deep water is changing in properties. There’s less of it. And that makes the deep ocean warm. So we have a lot of interesting observations, a lot of interesting things to think about. This is our take home graph on warming. There’s the title, “Global warming is ocean warming.” And there is our– let’s see, is there a pointer here? Yes, there’s a pointer. I’m going to show this. Here we go. OK, this is the total heat in the whole system, everything. So this is not just anthropogenic. This is it. There’s some funny units over here, zettajoules. This is years since we’ve had enough measurements to do this. There’s the total. OK, down here, there’s a little tiny purple line. That’s the atmosphere. That’s how much the atmosphere is warm. So there was huge press [INAUDIBLE] about the hiatus.

Anybody heard of the hiatus out there? There’s a lot of skepticism. Well, the skeptics could say, oh, the climate’s not changing, because look, it’s flat for the last 10 years. Well, that was flat in this curve down here. Is it flat in that one? Oh, no. What is this? This is the upper ocean, the upper 700 meters of the ocean. This is the deep ocean, below 700 meters. You see, this is the 93% we’re talking about. There’s bumps and wiggles. Yes, there’s climate variability, but there’s a relentless upward swing there. And most of the heat is in the ocean, thank goodness. But it also means that’s what’s happening. When we have these bumps and wiggles in our surface temperature, hiatus, et cetera, what’s happening is there’s an exchange between the ocean and the atmosphere. And the ocean is sitting there going, yeah OK, let’s have a mode.

And let’s take up some heat and change the temperature at the surface. But the heat in the whole system is going up. What’s this doing? Overall, the heating of the whole system. There’s the ice. The Greenland and Antarctic ice sheets are losing mass. Glaciers are continuing to shrink worldwide. That’s not the ocean so I’m not showing it. Arctic sea ice, et cetera. And the Antarctic sea ice has expanded, which is very interesting topic. And there’s workshops going on about that. That’s attributable to– the largest extent is in the winter when there’s no ice albedo feedback. It’s dark down there. And the wind is blowing stronger because of global warming. And the wind pushes the ice out. So the cover is going up. We’ve already seen these great pictures of the Arctic ice.

Here’s the ice sheet warming. This is Greenland, where it’s warming and losing mass. There’s the mass loss. This is Antarctica where it’s warming. Here’s the mass loss. You note it’s not the whole thing. So yeah, we’re going to be kind of happy with only– how many meters was that? – Six. – Six meters, as opposed to 180. Six meters of ice loss. As an oceanographer, we’re interested in this. You’ve already seen from Rebecca and from Maureen how the ocean affects the ice balance. This is in the Antarctic. This is the Antarctic ice sheet. This is the increased ice loss from the Antarctic ice shelves. And the ocean is a part of the culprit. It’s not just the atmospheric temperature, but the ocean is wrapping warm water coming out of the North Atlantic. It’s spiraling upwards towards Antarctica. Guess where it hits x marks the spot? Over here. So this is where it spirals in very close to Antarctica.

And we’re working hard on quantifying that in models, how much of this ice loss is due to accelerations of this pathway of warm water to the surface. So you don’t see the third dimension here. It’s going from 3,000 meters deep up to 200 meters. This is the mean state. This is the way the ocean is set up. So this is the incursion of warm water. And changes in that, probably due to winds, may increase this mass loss over here. Are the seas rising? Yes, you’ve already seen that they are. Here’s the IPCC summary. Rate of sea level rise has been larger than the mean rate during the previous two millennia. It’s gone up 20 centimeters. Well, 20 centimeters, oh, that’s not very much. You go oh, go home, sleep well. Who cares? Oh, well, with that 20 centimeters also comes an increase in the– and the more storminess– storm surges go up. There’s a change– there’s actually different rates for different parts of the tide. That aside, well, let’s say– well, the most important thing about that 20 centimeters is that it’s relentless. So I’ll show you a graph and to– First, I want to just give you a little pedagogy here on why sea level goes up.

It goes up for three reasons. Number one, the ocean warms so it expands. OK, that’s all that heat there. Number two, ice sheets, land-based ice melt. Not sea ice. Sea ice is like ice cubes in your iced tea. When it melts, your iced tea doesn’t overflow. But when the ice sheet melts, it does fill up. So you’re adding water to the ocean from glaciers and ice sheets. So the sea ice melt doesn’t change it, but the ice sheet melt, the shelf melting and ice sheet melting does. Those are two big factors. The third big factor in the change in sea level is rebound over thousands of years. You can go on this wonderful NOAA website and find information from all the long tide gauges around the coastlines. And you’d see a pattern, mostly up arrows. And these are from the tide gauges, some of our favorite ones.

The down ones may be the rebound. OK, La Jolla. We just celebrated 100 years of La Jolla records. It’s out at the end of the pier there. People are out there every single day making manual measurements of temperature and salinity. There is an automated tide gauge out there. 100 years– is 100 years enough was the question that was posed. Well, yeah. Should we stop? No. Don’t stop, because here’s the record. You fit a line through it. Relentlessly going up. Lots of bumps and wiggles. And if you only have 20 years, or you stop, what do you know? You’ve got to keep measuring it. So this tide gauge goes. And let’s move over to Boston. What’s going on here? Ooh, same answer. 1921, out there in the Boston Harbor, in this kind of very picturesque corner, is the Boston tide gauge that’s been there since 1921, maintained by the Coast Guard.

And the same kind of picture, bumps and wiggles, and a line fit through it going up relentlessly. You can make a map. This map doesn’t look like it’s going up relentlessly. There’s places where it’s blue, it’s going down. This is only since 1993. If you went back to these things and started in 1993, you might see sea level going down. So you’re seeing natural modes of variability superimposed on relentless sea level rise. So the idea is that it keeps going up. Here’s the projections. It should be up by at least a meter by the end of the century. OK. So last but not least, that sea level is just going to come up. What about our rain? What about our drought? What about the things that matter to agriculture? What about the things that matter to populations in arid areas? OK.

So what we’re going to be able to see here is that the ocean salinity is acting as a global rain gauge, which is great. We can actually learn a lot from ocean measurements that we can’t from just rain gauges on land. What we’ve found, to summarize and then go through why, is that since the ’50s, where the surface waters are saltiest, they’ve gotten saltier. Where they’re fresher, they’ve gotten fresher. That means we’ve changed the amount of evaporation and precipitation. It’s doing more of both. So places that are evaporating are evaporating more. Places that are raining are raining more. And that means that if you extrapolate that over to land, where you have arid regions, they become more arid. Where you have wet regions, they become wetter. So we have seen over the ocean enhancement of the pattern of evaporation minus precipitation.

This is some graphs from land which are showing this pattern, that will show it big time with the ocean, that the dry areas are getting drier, the wet areas are getting wetter. This is rich get richer, poor get poorer in terms of water. They can only measure that over the land. What we do with the ocean, these are the mean state of the ocean. The top plot is the surface salinity. Maybe something you’ve never looked or thought about before. Where it’s orange, it’s high. Where it’s blue, it’s low. You can see the patterns. And this bottom plot is showing evaporation minus precipitation. Where it’s red is where there’s more evaporation. Where it’s blue is where there’s more rain. And that matches up pretty well with the surface salinity pattern. So they’re very closely related to each other.

So the way you change salinity is you add water or you subtract water, because the salt is out there. It’s the dilution. You put in more water, it will get fresher. You take out the water, it gets saltier. So we can stack some plots. That plot of the evaporation precipitation is here. This is a world map in the middle. This is a world map of the salinity at the sea surface. And above them– well, I’ll do the once on top first. The one at the top is showing you the trend in the water vapor in the atmosphere. OK, the whole thing that drives all this is the atmosphere is warmer, so it can get wetter. So it’s holding more moisture. So it’s cranking more through, because it doesn’t hold a lot of water. Most of the water is in the ocean. That means it’s just picking it up and dumping it out, picking it up and dumping it out. So the trend in water vapor globally is to be more. There are some places that are drier. Mostly it’s wetter. This map that’s noisy, because our data is kind of noisy, is the trend in surface salinity. And it maps pretty nicely onto the actual map of surface salinity.

So that’s when we’re saying that the salty areas are getting saltier, the fresh areas are getting fresher. In this sort of noi– we have uncertainty measurements on that, this noisy sense. So surface salinity is suggesting that globally we’re having this change in the pattern. And then we can make projections up to the end of the century using all these climate models, which show this pattern of change in evaporation precipitation. So the trends look a lot like the actual situation. The actual mean state. So where it is evaporative, it becomes more evaporative. So you get dry. And where it’s wet, you get more floods. OK. So I am behind. I’m going to skip that, just to summarize and finalize. Climate change in the ocean.

Earth is warming now. 93% of the heat has gone into the ocean. Hydrological balance is shifting now. It’s strengthening now. Oceans are acidifying now. Ice sheets are breaking up and sea level rise is going on. All of these are projected to strengthen. So there is strong evidence for climate change. And I think that’s all. I’ll stop there. [APPLAUSE] – I would like to thank the speakers. And I’ll start off with a few questions to the panel. And in the meantime, we’ll have a mic set up, so if you want to ask questions, we’ll go until 12:15. So let me start off by asking, maybe Lynne and Rebecca, there’s big differences between the two poles and how they work in making the Earth’s climate what it is. And well, one big difference is the Arctic is in the ocean and Antarctica is a land mass. But there is a circulation around Antarctica. Maybe you could throw some light for us as to why the Antarctic ice sheet is not melting at the rate that sea ice is melting. And during the glacial interglacial fluctuations, there was a huge change in ice volume in the Northern hemisphere.

I believe not as much in the Southern hemisphere. So what are the big differences there? – I think you already said it. It’s inside out. So one is ocean surrounded by land and the other is land surrounded by ocean. And that just completely changes the way they respond to the winds. Both of them have wind patterns. The Antarctic sea ice area is out in the westerly wind bands. That’s like where you live right here up through Greenland. Whereas the Arctic is the other direction. There’s a lot of pieces of this. I don’t know where to start. So there’s a lot of ocean in the Southern hemisphere. There’s a lot of land in the Northern hemisphere. That makes it a different response. There are easterly winds ringing around the Arctic. And the easterly winds in the Antarctica are right along the coast. And they’re really important for pushing water into the coast. But the main wind pushes the ice out from Antarctica towards where it melts. So you have this– what we’re doing with global warming is spinning up those winds.

They’re getting stronger because the contrast in temperature are bigger. There’s bigger winds, and that’s pushing ice out farther. So even if the volume and so forth is a little different, the extent is getting bigger. There’s more– I think that’s the biggest one on the sea ice. And the Arctic is just warming. The Antarctic is only warming in the west Antarctic area. – Yes, I’d agree with that, basically. I mean, you’ve got just a very different geography, which allows different things to happen. So around Antarctica, we have the strongest current in the world, the Antarctic circumpolar current, which manages to isolate things down into Antarctica. In the Arctic, we don’t have that. We have an ocean we can flow waters into from either side. The ice in the Arctic is generally– it’s sea ice. It’s thin ice. It’s some meters thick. And the Antarctic’s a dirty, great big chunk of land ice which is kilometers thick. So you have a different whole climate associated with those things. It’s nice to have two poles, right? – During the glacial, was the Antarctic ice sheet much thicker? – So in North America, the ice that was over Boston was flowing from central Canada down to here.

In Antarctica, the ice expanded, but it was only able to expand out to the end of the Arctic ice shelf, which was more exposed because of the sea level drop because of the Northern hemisphere ice sheet. But then it just falls off the continent and flows away. So it really is– there’s no land for it to move northward onto. It’s limited by the size of the Antarctic continent. – So I have another question about what oceanographers call the meridional overturning circulation. So the oceans transport heat from the tropics to the poles. And there’s been a lot of papers that came out about the strength of this overturning circulation. From the paleo literature, we know that in the past, the strength of the circulation has changed. And so what is our current thinking? If we melt sea ice and we put all this fresh water up there at the poles, do we think that’s going to change the rate of deep water formation and the overturning rate? Do we have any clues from the past that– – Well, you could probably better speak to the future.

– I could speculate. – It’s certainly happened in the past. – That it shutdown? – Yeah, major reorganization of ocean currents. – So maybe you can tell us what you think is happening, or might happen in the future. And then Maureen can tell us– – And then somebody else out there can come up with a very different answer. This is pure speculation in a sense. Three sides there. What really regulates– OK, what we’re talking about here is the overturning circulation. You saw that warm water on Rebecca’s slides going all the way up into the Arctic. That is part of the overturning circulation. That water is going all the way up there, and it’s getting cold and sinking, and coming out. So that’s the North Atlantic part of the overturn. That progression of warm water up there is important in keeping passages open. It’s part of the Western European warming. That part– OK, that’s one part. And the Southern Ocean is the other cold part of the world, is isolated by the circumpolar current.

And we have a lot of ice formation right around Antarctica. It makes very dense water that goes to the bottom. So we have these two sources. We have one northern hemisphere, high latitude source that does not make deep water, which is the Pacific Ocean. And it’s our current experiment in how salt, or lack of salt, shuts down overturn. So the contrast between the Pacific and the Atlantic is the Pacific has a lot of rain and is very fresh, and the Atlantic has a lot of evaporation so it’s salty. So you put these two things at both ends of your table and you say, which one wins if you cool them both to freezing? Oh, the salty water will get dense and the fresh water will just float on that salty dense water. So that’s the simple picture set up by [? Stommel ?] and earlier, a long time ago, we have these two ends. And that balance only changes overall when you move the continents. That’s tectonics. So then the question is, what’s the vigor of those two overturns? The Pacific one is weak, it’s shallow. The Atlantic one is 10 times stronger and goes to the ocean bottom.

The question is if you add a lot of fresh water from all this melting ice on top of the North Atlantic, does it shut that circulation down, and then change the amount of warm water moving north? And so we had hints that all this fresh water was starting to weaken things a decade or two ago. The Northern North Atlantic was relentlessly freshening. But it turned around. And some of us went, ha ha. The circulation finally caught up. All that extra evaporation down off of here, off of the Gulf Stream over to Europe and Africa, the extra evaporation makes salty water that got pulled north and helped keep that cranking. So my speculation is that, yeah, the whole thing warms up. It becomes more stratified. You’re dumping more fresh water in the north, but you’re also pushing all this salty water in.

So you’ve got to have a balance. And I don’t know which way the balance will go in the next 100 years. You need to run a lot of models to do that. Maybe some of you have done that already. – OK, thank you. I’m going to pass it to the audience, because we have quite some questions. So please say your name and introduce yourself. – My name’s John Wigglesworth and I’m a secondary school Earth science teacher. And I spent a semester teaching about oceans and climate. And I wondered if you had any thoughts on how to give your message in a way that gives young kids some hope. [LAUGHTER] It’s something that I deal with all the time working with eighth graders and juniors in high school. And it’s a pretty sobering message. And how do you do it that gives people a sense of hope? – I’m happy to try to answer that.

So I’m actually extremely optimistic, even though it’s a very pessimistic message, just because I firmly believe that the limits of– there is no limit to human creativity and our ability to engineer our way out of this. But it has to start with the acknowledgement of the problem and an effort to reduce CO2 emissions. So I’m not sure, but I think people have to be empowered by knowledge of the problem and want to solve it. – So I would add to that– I struggle with this too. I teach a class on the Arctic. And you come to the end, you think, how can I end on some positive note? And I think it’s to remember in that that we do have the ability to change this. Right? If we go out there and see, we’re going to throw all the money that we’re putting into making ourselves rich into solving this problem, we can do it. Perhaps the most positive thing I saw in this was somebody said, right, I know seven technologies that could chip away at a seventh of this problem, of the CO2 problem.

But we have to teach the people that this is happening, that we have to face up to it, like we teach people to face up to problems in life. And go in and do it, and find on the way some way of predicting and mitigating it. So it’s their future. And I hope we can get them to grasp it and do something about it. And not just blame it all on our watch. – And I think something we can add is that there have been other problems for which there was no political will in the past, but when public opinion changed, political will came about. So I think there’s hope for that too. – So take the CFC ban. We managed to ban CFCs, because that was a science problem. So we can do it. We just have to team together and actually do it. – OK.

So the next question. We’re going to have to be a little quick because we have five minutes. – I’m Christina Hernandez. I’m a graduate student in the MIT/WHOI Joint Program in Oceanography. And I had a question for Rebecca about sort of ice edge blooms and the effect of melt ponds on under ice blooms. And so I was wondering if ocean color changes, whether those blooms happen under the ice during melt ponds or at the edges, if that contributes at all to these positive feedbacks that melt the ice. Like do you know anything about [INAUDIBLE]? – So this is really cool. So the idea is if you’re going to have a phytoplankton bloom in the ocean, you need to have nutrients, stratification, and light. If we get melt ponds in the ice, we get windows in the ocean which are allowing light to come into under the ice regions, which we always thought were devoid of life until the ice had melted. We’re finding there are those blooms in some places.

Quite why, we don’t know. We think because of the melt ponds, have they always been there? We don’t know. What is the feedback then from that phytoplankton trapping more energy into the ocean? Some– don’t quite know. We’re kind of working on that. Amala and I are working on that at the minute. So we can talk off line. That’s really exciting. – My name is Tim Johnson and I’m a software engineer. And I have one, I guess, a futuristic kind of question, in that it sounds like we’re heading for sort of an alien world. We don’t have to travel to another planet to find an alien world. We’re going to get one right here. I met that somebody was from Kuwait, and he said it’s 140 degrees Fahrenheit there and it’s getting hotter. And to me, that seems pretty alien. And it seems to me that we almost can’t stop what you’re describing. Even if we became much more politically active and the Republicans suddenly became totally different, we’re still not going to change very fast. Even if they changed it tomorrow, passing legislation, changing things.

And so it seems to me we have almost a whole new area of science of how to deal with the fact when the world is going to change over the next century, because it really is. Is this sort of something people are thinking about, like most businesses are looking how to make money? Like you can have tours taking you through the Northwest Passage which didn’t exist before. But it seems like a sort of a big area. I suppose it’s a way to make a lot of money for some. That may encourage some Republicans to do it. – There is a big burgeoning of renewable energy. And you can see it around the world. And Europe is just going bonk– it’s great. It’s the future. And the US is going that direction too, slowly. There’s a whole area of adaptation and engineering that is very active. So encourage your students to go and work in that. But don’t eliminate the basic science, as the Australian government did for a brief period the last year.

They said oh, we know the answer. Climate is changing. We don’t need you guys anymore. Let’s put all our money into making some money on adaptation and engineering. And there was a big kerfuffle, because when you have cancer you don’t stop taking your temperature because you know you have cancer. So we have to have both legs of that. We don’t represent that end here, but maybe some other people can speak to that. It’s very active. There are some geoengineering ideas out there– scrubbing the atmosphere, clean up your mess. – So if I could just add to that. Portugal, I think, ran entirely on renewable energy for a period of time this last summer. OK? So it can be done. We just have to decide we don’t just want money, we want a world for our children, as they say. – OK, thank you very much. Thank you all for being here.

And of course, John. – Thanks to the panel. [APPLAUSE] And I’d also like to take the opportunity to thank Amala. She helped consult as we were developing this program, and was extremely helpful to shape it. So you deserve a lot of credit for this. [MUSIC PLAYING] .