Sustainability Videos & Lecture Series

Wallace Broecker: Well, it’s really a pleasure to be here. My wife, Elizabeth, and I are being treated like minor royalty. I’ve spent some time here. For five years I was involved with Biosphere 2 as some of you know. I did my PhD thesis partly around Pyramid Lake near Reno, and now am interested in what’s going to happen to your water. If I were you I would worry, and I would do everything I could to reduce the build-up of CO2. It ain’t going to be good for you. I think that the climate here will turn more like the Mohave or worse.

In this lecture I want to show two things. One is something that’s indisputable, and that is that water availability out here is incredibly sensitive to climate, and it’s changed a lot. I’m going to talk about a period of time that goes back about 20,000 years, and I’ll have two key times. One is 15,000 years ago, and the other is 1,000 years ago. 15,000 years ago it was extremely wet here, and 1,000 years ago there was a huge drought, a hundred year drought.

Now, as you see here this is sort of a doctored up photograph from our map of the Great Basin. The Great Basin extends from the Sierra Nevada and west to the mountains in Utah in the east, so from Salt Lake City to Reno. It’s sort of petering out down here, yet extends up into Oregon. What I’m showing here is the coverage of standing water 15,000 years ago, and that’s in blue. The white is what’s left before irrigation reduces it even more by stealing the water from rivers so it doesn’t go into the lakes. So you see that there’s an order of magnitude difference in water coverage. This is a closed basin. No water gets out to the sea. Any rainfall or snowfall has to–the only way back out is to evaporate. At times when it’s wet these lakes expand in size because they have to be bigger so there’s more evaporation, and at times when it’s dry they get much smaller.

Now, you might wonder how in the hell can you get a tenfold increase in the size of a lake if it were just rainfall, but we have ten times more rainfall because those lakes would be evaporating ten times more water. That can’t be true. Volume could increase evaporation so let’s say it’s three times rainfall, three times evaporation, that’s beyond anything we can imagine.

So there’s one other factor–well, let me go back. This is one of these lakes that you saw in that big picture. This is in Nevada, and so Reno would be right here on the Truckee River. The red areas are the areas of water coverage before the Industrial Revolution. This is almost dry now. This is dry now. We have Pyramid Lake, Silver Lake. The pale color here is the size of the lakes during the peak glacial time, so it would be about 20,000 years ago. The blue, which you see is bigger, is what it was 15,000 years ago, and has a very interesting story which I will get to.

This is a picture of Pyramid Lake. It’s a beautiful place. If you’re ever in Reno and haven’t seen this lake, it’s about an hour drive to the northeast. It’s an Indian reservation. There’s an island here and pyramids somewhere, and I’ll show you a picture of those. Here’s the pyramid after which the lake is named, and that’s the island. What you can see easily is that there are drawings–15,000 years ago only the tip of that island was sticking out of the lake. It’s a huge lake.

Now, I didn’t explain how this lake got so big. There’s an important aspect of water budget and why this deflection of water, it runs off. We get rainfall onto a drainage basin. Much of it is transpired through plants, and some of it runs off into rivers. Where I live in New York, about 50 percent of the water that rains runs down the rivers, out here perhaps only seven percent. You can see this map shows worldwide the fraction of runoff, and you see there’s an awful lot of the world that is below 30 percent and quite a bit that’s below 10 percent, so you’re down in here somewhere.

It turns out that as you increase rainfall, the amount in any given area, the amount of runoff increases, the fraction of runoff increases. If out here you had a ten percent increase in rainfall, you’d get a 30 percent increase in runoff, so if you had a twofold change in rainfall–that’s probably what happened 15,000 years ago–you would get a six fold increase in runoff. This is important because much of dry land agriculture is irrigated from reservoirs, and of course, reservoirs would be just like these lakes. They depend on not only the rainfall, but the fraction of runoff, so the amount of water reaching reservoirs is going to change with climate one way or the other.

Now, at the other extreme we have, to gauge dryness is much more difficult because in these lakes the shorelines are underwater and they’re very hard to study. They’re very hard to date, so we don’t know much about that. I give you just one example of something that happened out here that we really don’t understand, and that is that roughly 1,000 years ago, 800 years ago actually, there was a fantastic drought that was far more intense than any drought you’ve had in historic time and far longer in duration. Droughts are normally like five years, and this one was 120 years. There were two of them back to back separated by about a 25 year, 30, 40 year wet period. Each of them was a century drought.

How we know that–well, Scott Stein at the University of California was driving along Route 395 where it parallels the West Walker River, one of the rivers feeding Walker Lake down here. He noticed these stumps sticking out, so he went and chopped off the top of one of them and counted the rings. He found that these trees had lived up to 120 years, something like 120 years. Now, these were Jeffrey pines. They’re killed when their root system is underwater for just months. There are 84 of these trees and they’re all over the channel of this river, so the only way to explain their existence is the river was dry for 120 years. Now, this is a very healthy river coming out of the Sierra Nevada Mountains. It must have been drier.

So Scott Stein went and looked at Walker Lake itself, so if the rivers feeding it were dry it should have gotten smaller. Well, an experiment has been done by man on Walker Lake and that is to cut off its water supply by taking it all for agriculture. Almost no water now gets out of the Walker River into Walker Lake, so it shrunk to about half the size it was in 1850. In the shore zone it’s been abandoned. He found all kinds of small desert vegetation, and he could date that by radiocarbon. He showed that, as you would expect, that the rivers were dry. The lake was at least as small as it is now during that time.

My point is that this region, the precipitation and sort of hydrologic state is very, very sensitive to climate. We are now experimenting with the world by adding CO2 to the atmosphere. I firmly believe that this is going to warm the earth, and it’s going to make a lot of differences. Some may be good, but most will be bad. One of the things it’s going to do is during the transient while CO2 is building up there will be a lag in warming because of the fact that the ocean has to be heated up. It takes an enormous amount of energy to warm up the ocean, so that’s delaying the warming. Maybe we’ve only reached half of the warming that we would have for this amount of CO2 if we gave it enough time to warm up the ocean.

What’s going to happen–all the models say that we double CO2, and by the way, we’re at 400 parts per million. We started at 280. We have to go another 160 to get to double CO2, and we’re going up at 4ppm a year. That means 40 years at the present rate. This last year was the largest amount of fossil fuel burned ever, nine gigatons. I think that because of China, India and all the other developing countries that the rate of rise of CO2 is going to get even greater despite the fact that we’re doing some things in developed countries. The other countries are eclipsing any savings we’re making, so the time for doubling may even be shorter, but of course it’s a complicated world. It’s hard to predict how much fossil fuels we’re going to use, but I think there’s no way we’re going to–85 percent of our energy comes from fossil fuels. In order to stop CO2 rising we’ve got to cut that back to about five percent of our energy supply. It’s going to take a long time. There’s no doubt about it.

Now, one thing that isn’t talked about in global warming is that the warming in the northern hemisphere during the transient is going to be about twice as much as the warming in the southern hemisphere. As models say if we double CO2 we should get something like 3.6 degrees centigrade with an error of maybe one and-a-half. Let’s just take 3.6 degrees centigrade warming, so if the northern hemisphere warms twice as fast as the southern hemisphere it will warm up 4.8 degrees and the southern hemisphere 2.4. When we average that we get 3.6. It’s going to create a big difference in temperature between the hemispheres, and that’s going to move the thermal equator to the north. The thermal equator carries with it the major rain belts.

A similar change occurred 14.7 thousand years ago when suddenly Asian circulation reorganized and sea ice cover changed. I’ll show you a bit of that. The northern hemisphere warmed up like mad. The southern hemisphere may have even cooled a bit, so the thermal equator moved to the north just as it’s going to do. It’s in a sense an analog, and I’ll mention it’s not a perfect analog, so you may luck out. What happened 14.7 thousand years ago is what’s going to happen in the future. That’s going to be very bad news.

This is a record kept on Antarctic ice, and the period we’re going to be interested in is the Big Wet so it’s during the time of deglaciation. You notice that Antarctica, as indicated by the hydrogen isotope ratios in Antarctic ice, started to warm about 18,000 years ago, kept warming until this 14.7 time more or less and then it stalled and cooled a bit. Then the rest of the warming was during a time we call the Younger Dryas. Paralleling that rise in temperature was a rise in the CO2, which looked very much like it. Someone might say perhaps CO2 was driving the warming. CO2 was coming back out of the ocean. A fair amount of the atmosphere’s CO2 had been sucked up into the ocean during glacial period. They had given back during this time.

In the northern hemisphere we had quite a different thing happening. This is recorded in the same ice core. This happened to be methane, but this methane is a direct reflection of the climate in Greenland. It has to do with the fact that many of the swans on the earth were knocked out during a glacial period because of ice and permafrost cover. Again, in the southern hemisphere at the end of this time there was a stall in the warming and a stall in the rise in CO2. In the northern hemisphere there was a profound warm up, a very, very interesting time.

Now, by my best friend, George Denton, we learned an interesting thing. Gary Comer, who founded Lands’ End, adopted a bunch of us to do this kind of abrupt climate change research and took us to Scoresby Sound, which is a red dot on the east side of Greenland. George measured the snow line lowering during one of these cold periods and found that that was equivalent to a temperature drop of only about four, five or six degrees.

One of my former students Jeff [inaudible 20:46] had done work on an ice core in the middle of Greenland and said that the mean annual temperate changed about 15 degrees, and so either one or the other has to be wrong, but we are convinced that they were very, very cold winters. Winter temperature change was somewhere between 20 and 30 degrees, and the reason for that was that deep water formation, which now occurs in the area around Iceland, was shut off by a big burst of ice that went out into the ocean from the continents, melted, put a fresh water lid on, and the next winter that froze over. That changed the climate in Scandinavia from what it is now–we’re at fairly mild, to what would be like Siberia because no heat could come out of the ocean through that ice cover cap and any sunshine that fell on the ice would be largely reflected.

When this happened it cooled the northern hemisphere and created one of these inner hemisphere temperature differences. What we see here is the Amazon forest in green and the excursion of the rain belt in today’s world. Over the Pacific the rain belt moves only a small amount from summer to winter, in the Atlantic and Pacific, but over land it moves a lot more. The seasonal sweep of rainfall in the Amazon is much wider.

We have records from four places that indicate that during this time when there is massive ice cover in the north the Amazon high rainfall area moved to the south. The circle over there is from a deep sea core that shows great increase in river-born debris, a very large increase. The square there is a cave that’s been dry for most of its existence in most of this time interval, and only during times when there was excess sea ice in the north was there water going through the cave and stalagmites formed. That’s well dated, so the stalagmites formed for short periods of time when there was ice cover in the north Atlantic.

By contrast in the Cariaco Trench north of South America the opposite happened. The rain forest moved south. You had more dry land with less run off and it shows up in the sediment. This is dramatic what happened here. This is the Altiplano. You can see where it is. It’s sort of southwest of the Amazon basin. Most of you know about Lake Titicaca, which is a large closed basin lake in the northern part of the Altiplano, a very high area in Bolivian. In the southern area it’s mainly very, very dry. There’s a little lake here. During the 15,000 years ago–so here’s Lake Poopo. During the main glaciation this lake in the south was this pale color, and then 15,000 years ago when there was this massive sea ice the lake got even bigger. This means there was a lot more rainfall in there. This is the area by the way in the second to last James Bond movie where the guy staggered to death from lack of water. He deserved it [laughter].

Now, there’s another record and that is–I’m going to show you that when these lakes got very big here and on the Altiplano the monsoon rains in China weakened. What this tells us is the whole hydrologic system of the tropics was impacted. We’re going to be talking about just the last 25,000 years, so just this interval over here. Larry Edwards at the University of Minnesota and his coworkers have gotten stalagmites from several caves in China, and they measured the oxygen isotopes and they showed a cycle of variation of peaks that are spaced about 20,000 years.

This is related to the procession of the earth’s orbit. I’m not going to take time to explain it, but the earth’s orbit is eccentric and therefore sometimes the earth is closer to the sun than at other times. Because it processes, the summers in the northern hemisphere, let’s say, are extra warm at some times and somewhat cooler at other times, so it modulates the seasonality.

The red curve there is the solar input in, what is it, on July 21st at 65 north, so this is a reflection mainly of the procession of the earth’s orbit like a top. Well, I’m saying it takes 20,000. It’s a little more complicated than that, but we don’t need to get into that. If you count those peaks back to 200,000 there’s about ten. Now, when he measured that–he dates these very accurately. He’s an amazing guy. The 100,000 years in the stalagmites he can do with an age error of 60 years. That’s amazing. He did a study of the last 1,000 years and he could do an accuracy of one year then, and what he found in this record of the last 1,000 years is that the monsoons weaken three times per decade, decade and-a-half. In each of those times there was a dynasty change in China, so he can date so accurately there’s no doubt about that.

That suggests that the heat–you know, the rice crop failed, that it was weak. People got angry and heaped on the government–I don’t know, but it’s a good story [laughter]. Certainly the Chinese government didn’t change the monsoons. When you have strong monsoons the isotopic composition of the rain is deficient in the heavy oxygen isotope 018, so it’s C -9 out there. If you have less monsoon contribution, if the monsoons are weaker, then the isotopic composition of the rain shifts to less negative. This is a beautiful record that shows that that’s happening.

Now, I want to look at just some of this fine structure on this right in here. That’s the same red line, and I’m now just showing you from 18,000 years to 10,000 years, so here’s the time when the Great Basin was extraordinarily wet and the Altiplano was extraordinarily wet. The monsoons were weak, and so they were going in here and they drop, and so you might think of the red line as a reference. If they were just slavishly following procession, they’d follow that smooth curve, but they didn’t. This is a transition that I’m interested in about 14.7 thousand years ago. You see the monsoons got stronger.

We’ve been trying–I’ve been working with Larry Edwards in Minnesota, Jay Quade who’s at U of A, and others to try to look at all of this on a global scale. Where I can’t on this lecture explain all of the details, there is no doubt that these changes were globally orchestrated. I’ve talked about Lake Lahontan whose remnant is Pyramid Lake. I’ve talked about the cave in eastern Brazil. I’ve talked about the Altiplano, but it turns out that the Dead Sea in Jordan did exactly the same thing: went from large to small. On the other hand, and I’ve said that the monsoons in China went from weak to normal or weak to strong in the opposite sense of the changes in the other places.

One more place–a man named Tom Johnson in northern Minnesota, Minnesota/Duluth, studied Lake Victoria. He took cores in it and found that each piston core was stopped by the hard soil there which had grass on it. The sediment right about that soil horizon had a page right here, so the lake was dried at the end of this period. We don’t know any more about it because the cores don’t go any deeper, and then it came back to something like its present size during this interval. Lake Victoria sits right on the equator. It’s a big lake. It feeds the Nile, but it was dry. A seismic survey showed that the soil horizon was everywhere under the present lake.

Okay, let’s see. How am I doing on time? I want to leave time for a lot of questions. Let me summarize. There is no doubt that the amount of rainfall coming into this area and to the north has changed by a lot, so 15,000 years ago there were a lot more and 800 years ago there was a lot less. That’s sort of anecdotal. I don’t know how that fits in, but another thing we’re doing is that the main glacial period was about 20,000 years ago. From like 1250 to 1850 A.D. was what we called the Little Ice Age. It was about ten percent the cooling of the main Ice Age, and it had all the mountain glaciers expanded and so forth.

We’ve been studying the hydrology and found that in China, for example, in a desert in western China was much better during the Little Ice Age than it has been in the last 100 years. That’s a big lake that’s now gone. There were myriad of poplar trees growing in between sand dunes and this desert. They’re all dead. We’re going to have to worry that what we’re doing is going to move rainfall around. It’s not going to change the total rainfall on the planet, but Isaac Held who just won the award that was mentioned at the beginning, BBVA award in Spain, showed that as you warm the planet the tropics get moister. They get more than their share. They’re already getting more than their share, but they get even more than their share, and the extra tropics get even less.

The tropics are stealing the rainfall from the rest of the planet and therefore the rest of the planet on the average gets drier. That drying is mainly in the latitude zone of 20 to 25 degrees away from the equator. That’s been confirmed now by all of the large global circulation. Global climate models all show that, so they show that as the planet warms tropics get wetter, extra tropics get drier. And if they were on a cooler planet, they get the opposite. That in itself isn’t encouraging for you because we’re going toward a warmer climate.

What should we do about this? I’ll probably talk about this in other lectures, but there is going to be a 50 year transition where we’re trying to wean ourselves off of fossil energy and go toward other energy. Don’t kid yourself. It’s going to take a long time. During that time CO2 is going to continue to rise. I think that unless we start to do something it’s going to climb not to double the CO2, but up to triple the CO2. That’s like five degrees centigrade warming. That’s really a huge, huge change in climate on the planet.

I think we’re going to do one of two things. There will be any number of scenarios. One would be to heavily implement carbon capture and store it and thereby take the CO2 out as fast as we’re adding it so we could quell the rise. On the other hand, we go business as usual which we’re on the track now. In fact, it’s warming faster than the extreme IPCC case, so they had an extreme and we’re above the extreme. If we do that CO2 is going to build up, and then it’s going to warm a lot and people are going to try to demand how can we cool it off.

Well, unfortunately there is a way to cool it off and that’s by putting SO2 in the stratosphere. It makes sulfuric acid droplets, and they reflect away sunlight. We could counter the warming at, unfortunately, a modest cost, so if we go business as usual–but why don’t we get into this in the interim. If we don’t take the CO2 out as we inject it, don’t pull it out of the atmosphere, then after we get to Utopia, which could be a planet run by other kinds of energy, we would be left with a lot of CO2 in the atmosphere. We would have a climate that would threaten to slowly melt the ice caps and raise sea level, a climate that’s changing the ecology of the whole planet, blah, blah, blah.

We would then do what we should have done before, and that is we have to have a device which will pull CO2 directly out of the atmosphere. I know enough about that to know it’s entirely possible. I also know that the total amount that’s been spent on research to take it directly out of the air is about $10 million total. One of my Yankee pitchers makes that a season, in half a year. I mean, there’s something wrong that when there’s an obvious way to do something that we don’t spend some money to see whether it really works and what the environmental effects are and so forth. These things take a long time, and now I don’t think we’re going to do anything about global warming on a global scale for at least 20 years. I mean, politics have turned against it, but in that time there’s a lot of preparation we could do that wouldn’t cost all that much money, so that’s my message. [Applause]

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The above transcript provided by Landmark Associates.