George L. Jacobson is Professor Emeritus of Biology, Ecology, and Climate Change at the University of Maine.  Since his arrival in Maine in 1979, Dr. Jacobson has been a member of the Climate Change Institute, and he was Director of the Institute for nearly a decade.  His scientific research has focused on long-term climate variability and specifically on forest responses to climate changes during the past 60,000 years. An important segment of his research has dealt with the implications of paleoecology for both present-day conservation biology and climate science. The research examines how communities and ecosystems have adapted to natural climate variability. Prof. Jacobson’s projects have included sites in North America, South America, and Europe.   Among other things, he has served as an external advisor on climate to the European Science Foundation, and to the Finnish Academy of Sciences.  From 2008 to 2014, he had the honorary designation of Maine State Climatologist.

Professor Jacobson joined the faculty of the University of Maine in 1979 after three years working in the United States Senate in Washington, D.C., first as a AAAS Congressional Science Fellow and then as a staff scientist for the U.S. Senate Committee on Environment and Public Works.  He was born and raised in Rapid City, South Dakota, and earned a B.A. in 1968 from Carleton College, and a Ph.D. in 1975 from the University of Minnesota.  From 1968-1970 he served as a medic in the United States Army.

Full Transcript

I really appreciate the invitation and I'm honored to be here with you today. As you heard, Doug is my younger brother, but he and the rest of my siblings actually grew up for much of their lives in Santa Barbara. I never lived there because our father died in 1965 when I was a freshman at Carleton College. Mom had five children at home at the time, including a six-month-old baby. She moved, took the family shortly thereafter back to the Monterey Bay area where she'd grown up in Carmel. Her parents had encouraged her to move so that they could help her.

Mom had a degree in microbiology from Berkeley. When my youngest brother, the one who was a baby when my dad died, was old enough to start school, she moved to Santa Barbara and got a very good job in the county health department as a microbiologist and had a career there. By herself, she raised all my younger brothers and sisters and they're all doing great. The one who was a baby is now in the senior foreign service in the state department. All is well. Our mom died a couple of years ago and we are still in awe of what she did.

What I'd like to do is give you some perspectives of the things I've learned during my career studying long-term climate dynamics. As you heard in the introduction, I've been part of a research institute here that was founded almost 50 years ago. Next year will be our 50th anniversary. The climate change institute was set up in 1972 as a way of studying the history of the Earth's climate using many different disciplines. During the past recent years, we've had research sites where all the red dots are in this map and many more. We have biologists and several kinds of geologists and oceanographers and atmospheric scientists. We have four archaeologists, all of us looking at different aspects of Earth history and trying to get as many clues as we can to how the world has changed through time and how the world's climate has changed through time.

Although our individual projects all vary considerably depending on the location and the particular problem, I think that as a group, our collective goal is to understand the question I've listed below, namely identifying the natural variability of the Earth's climate and the mechanisms that lead to that variability. This is something that we've been doing long before the current issue of global warming really appeared on the horizon, or at least in public very much. It wasn't on our horizon, but we were really just interested in understanding what made ice ages happen and how did we come in and out of ice ages so quickly and so forth. And how did people react to changing climate and how did forests react and things like that?

Well, it turns out that having this understanding of long-term variability is essential to understanding what's happening today. Because if we don't understand what the natural background variability is, how can we possibly say whether what's happening now or in the future is unusual? We have to know what the natural expression of the Earth's climate would be and its changes and why. So that's what I'll talk to you about and talk about quite diverse climate perspectives and time perspectives more than you're probably expecting, but I hope you'll bear with me.

I would also say that any time during this talk, feel free to speak up and ask a question. I don't mind a bit being interrupted and I'd be happy, I most prefer to discuss something that's interesting to you on the screen or point I just made right on the spot rather than come back to it later.

I'll start out, if you don't mind, sharing a little bit about this wonderful state of Maine where I live. I was lucky enough to do one of my teaching roles involved teaching a graduate course in plant ecology and that allowed us to take weekly field trips in many parts of the state of Maine to look at different kinds of vegetation and environments. Maine is defined by a lot of variability in its climate and topography and geology and so forth.

This is the map that shows the plant hardiness zones that you're familiar with from going to garden centers, probably. You know when you buy a new shrub or something there's a little thing stuck in the soil that says what zones these can grow in. Some are for colder places or warmer or things like that. And this is the map that was created in 2012 for the state of Maine and it shows quite cold zones. What the map actually shows is how severe the winters are because that often is the determining factor in plant distribution. It's not the only one, but in the West it's more often moisture and things like that. But in the East it's more likely to be severity of winter conditions and this would be true over most of Europe as well.

In the northern part of our state we have a very continental cold climate very similar to say northern Michigan, northern Wisconsin, Minnesota, places like that. Whereas on the coast in the south, because of the warming influence of the Gulf of Maine, the temperatures and moisture regimes are very different and it's a much milder climate. So within our state we have a big range of growing zones as defined by this map. As you can read there, the map was updated most recently in 2012 and that's because the 1991 was already out of date and my guessing that we're about due for a new one again because these are changing remarkably fast.

But just to put this in perspective, the variability we have compressed into four degrees of latitude in Maine, from north to south, is great because of the maritime influence in the south and the continental extreme interior climate in the north. It's equivalent to the climate variability between northern North Dakota and central Kansas. Isn't that interesting? It really compresses the entire climate region and that whole central part of the country into this little northeastern corner of the country.

And if we compare it to Europe, Maine's four degrees of latitude, and the climate in that four degrees is essentially the same as the variability in climate from northern Finland to central Poland. So there's a huge range of variability, but we can recognize that that's true even looking at natural systems because there are peat bogs of a certain type that grow in northern Finland. They also grow in northern Maine, and there are peat bogs of, there's a whole range of them, but the southernmost type of peatland grows in Poland and we have those in southern Maine, and that's because they're driven, they're controlled really in their dynamics and their ability to exist by the climate of the region. So that's where I came from. That's just a little introduction to this great state, but I hope you, if you haven't visited, you're more than welcome and you'll find it to be a beautiful place.

Now, I'll just start, you're all familiar, I don't need to preach to the choir here about climate change and fossil fuel and all that, but I just like to go over a few basics so that we can start thinking about this. As we all know, industrial use of fossil fuel has led to huge increases in atmospheric CO2. Almost 10 years ago, we had added 500 billion metric tons of carbon, you know beyond what would normally be in there to the atmosphere by burning fossil fuel, and it's still going up rapidly despite efforts to control it. But you know when we think about even things like the Paris Accord that was agreed to and then we got out of it and got back into it, that's only to agree to go to 1990 levels. That's not very impressive really in the big scheme of things is it.

We know by the laws of physics that greenhouse gases, CO2, methane and others trap heat in the earth and increase the temperatures in the lower part of the atmosphere. And there are lots of examples we're familiar with. For example, those of you who've ever lived in a cold place know that when it's cloudy, the temperatures never get very cold. In fact, when it's snowing, it's a good frame of reference for anybody who's lived in a climate that had snow. During a snowstorm it's almost never very cold it's usually 20 degrees Fahrenheit or something like that. And then the next day when the sky clears, and we see the stars in the late afternoon, we know tonight's going to be really cold. And that's because the water vapor in the atmosphere is a greenhouse gas. And when the clouds are present, the greenhouse gases, namely water vapor trap that heat until the clouds disappear.

Well, the difference in the greenhouse gases of water versus say carbon dioxide is that water droplets in the atmosphere and water molecules in the atmosphere have a residence time of two or three days where in the case of carbon dioxide, the molecules in the atmosphere that build up have a residence time of several centuries. So the implications for long term climate change are very different among the two. One's important for weather, local weather, the other for climate.

We know that the amount of heat in the atmosphere has reduced sea ice in the Arctic and elsewhere and melted glaciers. This is something we read about in the news, practically every week. And we know that sea level will, as a result of melting glaciers will rise probably between one and two meters by the end of this century, easily a meter, it could be more. Concerns are, should be greater than they are even. But places like Miami right now are trying to deal with the fact that even under regular high tides, the sea is coming up in the middle of their neighborhood.

Now this is a reconstruction by NASA of the sea ice in the Arctic, and it started back in 1984, this particular visualization here. And the ice, this is, years are going by in the upper left corner, 1991, 92, you don't have to read those, but each of these cycles back and forth is one year, and the very bright white ice in the Arctic Ocean is ice that's several years old. And that can, it builds up and could be several meters thick. The light gray areas are sea ice formed only in the previous winter. But watch what happens now as we get into this, we just passed 2000, 2001. Keep an eye on what happens now in the last 10 or 15 years leading up to now. This series will end actually in 2016, so it's not even quite up to date. But watch what happens now in the next few years. Here's 2007, 8, 9, 10, 11, 12, 13, 14, 15, 16. And so, we see how dramatically the amount of ice and especially the amount of old ice in the Arctic Ocean has changed and this is why ships are starting to pass through the Arctic Ocean from Asia to Europe and North America through the Arctic instead of through the Panama Canal, and so forth. So that's one outcome of what we, there are many outcomes that are already evident about the changing climate. And we've started to see changes that were, say, outside the normal variability going back to roughly 1980.

Now, there are a couple of people I'd like to mention today in the history of the science related to this who stand out because they had a crystal clear understanding of the problem. And despite being discouraged by others, refused to stop studying and speaking about this. And one of these really interesting people is a Swedish chemist named Svante Arrhenius. He was a student at the University of Uppsala and he was a chemist and his PhD research was about electrochemistry, which has a variety of things to do with things like batteries and electroplating and it's a major thing in the world of industry and science. But his work was so groundbreaking that his own professors at his own university chemistry department didn't believe what he was talking about and they barely granted him his degree, because they didn't think what he was doing was in line with anything correct. And so, he was a very good student.

But one of the interesting things about European graduate programs to this day, at least in the Scandinavian countries, and I've been familiar with them by being part of this process a number of times. They don't have to be awarded as a PhD rather than have a draft that a few people in the university see and then have a thesis defense and then they're awarded their degree. In the case of these European universities, the students actually have to publish, print up and publish their dissertation, and then distribute it throughout Europe to people in the field. And then they're awarded the degree of PhD in the defense. And then, if anybody wants to can come to the defense and ask questions. So it's a, this would be an absolutely terrifying thing for most American graduate students believe me, and it terrifies a bunch of the Swedish ones today too. And so, it's been a very nice way. It's quite an interesting process.

But Arrhenius was finally granted his degree, but his professors were sure he wouldn't amount to anything, until about two months later when all the great chemists of Europe started showing up at his door to talk to him. Because they realized how important his work in electrochemistry was. And about 10 years later, it was awarded the Nobel Prize in chemistry. So, he stuck to it.

Now what's interesting about it from the climate point of view is back then he realized there was a fellow named John Tyndall from Britain who had developed spectroscopy and understood that certain molecules trapped longwave radiation, which is what the Earth's heat is and when we talk about greenhouse gases, it's trapping long wave radiation. And Arrhenius realized when because of the increasing combustion of fossil fuel for industrial purposes in the early part of the 20th century that that if we kept doing that and adding greenhouse gases, namely CO2 to the atmosphere, that the Earth would warm up. So for 10 years he went around Europe giving talks. He sort of put aside his chemistry, or at least his sideline to it. He went around giving talks about what he called a hot house world. And he was warning people that burning fossil fuel would lead to problems in the long run. Now, and of course he was right. He was wrong about one thing. He estimated that it would probably take five or 600 years before that happened. But little did he know how the industrial use of fossil fuel would change.

There's one more person who's really interesting and that's the person responsible for this famous curve. You've seen this curve of carbon dioxide as measured in the Mauna Loa Observatory in Hawaii. And I put the latest reading from two days ago on here, June 3. The reading was 419.7 parts per million carbon dioxide in the atmosphere. David Keeling is the one who's responsible for starting these measurements. And this happened back in 1957, when there was a year, geologists didn't have satellites or any way to have global monitoring of anything. And so there were only spotty records of any kind of Earth conditions really. And the geologists involved decided that in 1957, they would everywhere on Earth make the same measurement. So there could be essentially a snapshot of Earth conditions at one during one year. And so there were many proposals made in the years leading up to this for which kinds of things should be measured. And so there were lots agreed upon.

And one of the proposals came from David Keeling, who was at the Scripps Institution of Oceanography in La Jolla. And he suggested that carbon dioxide in the atmosphere should be measured. That would have never been done. And but he was aware of the greenhouse buildup of CO2 from fossil fuel, and he thought it made sense to start measuring this and see how that varied globally. But he was turned down. There were requests. These were all requests for some funding to go do these kinds of measurements. And Keeling was turned down. And but fortunately, like Arrhenius, he didn't take no for an answer. And he just went and set up the observatory himself and started making the readings that lead to the left end of this curve. And of course, after two or three years, it was obvious that every year the amount was going up. What we see in that little sine curve is the basically the photosynthesis and decomposition in the northern hemisphere forests. That's basically where most of the biosphere carbon is locked up. And the photosynthetic part of the year takes CO2 out of the atmosphere and the decomposition in the fall returns CO2 to the atmosphere until the next spring.

So that's what those little sawtooth curves are. But this long term increase was documented at the Hawaii Observatory, thanks to Keeling's persistence. And of course, he ended up being famous and appreciated for this a year or two ago. Very interesting case. I've often told students how important it is, and it applies to all of us, when we understand something really clearly. Even if other people don't understand what we're talking about, don't give up because it's really important to stick to our guns and follow through on important things, even if we're alone for a while because things can change as we know.

The way we know something about CO2 in the atmosphere back before 1957, of course, is in ice cores. And you've heard about this. These are some colleagues in our Institute who collect ice cores from Antarctica and Greenland and certain high mountain glaciers and places like that. This is a photograph from some work in Antarctica. But these ice cores are taken sometimes down as much as one or two kilometers below the surface. So they're long term records. The snow that builds up on the surface and eventually turns into ice is analogous to sediments in the oceans or in a lake. And it's just frozen water. But it turns out there's an enormously interesting and complicated record of the Earth's atmospheric chemistry locked up in these ice cores. And those are the reasons my colleagues are studying them, collecting them.

This figure, which starts about 800,000 years ago on the right going back to the left, shows the variability in CO2 in the Earth's atmosphere for that 800,000 year period. Except for the very left hand part of the curve where, as you can see, the... let's see if I can make myself a... Well, did the wrong thing here. I was trying to make myself a pointer. But anyway, this upper part of the curve is based on the measurements in Mauna Loa and also a short ice core from Antarctica. And the two overlap where they overlap in time. They show the same measurement. So we know this works.

But this shows a record of sawtooth curve of CO2 in the atmosphere that represents a series of ice ages. And I'll come back to that in a minute and talk about the ice ages. But the point I want to make here is that the natural variability of CO2 in the atmosphere during these eight ice ages of the last 800,000 years is outlined by these yellow or green lines I put in here. So the natural variability ranges within those bounds and you can see how far we're already moving out of the natural variability of CO2. It's really something extremely outside the boundaries of what the Earth has experienced for several million years at least. And here's the 419 parts per million as of today. Anyway, this is a curve of CO2 in the atmosphere.

And now I'd like to go back and talk about some other things. This is a botanical quiz to start this off. This is a plant that is found in Maine. It's a special quiz for you. I know some of you probably are gardeners and have an idea what different plants are. But I wonder if anybody recognizes this, let me know. If you don't, that's okay. But this is a plant, it turns out it's very unusual looking. And it's unusual looking because it was, well, for one thing, it was living 400 million years ago in what is now Maine in the Devonian period. This is a plant called Pernica quadrifaria, and it's of interest that its connection to Maine is accidental. It just happens we have rocks of that age here.

But it's interesting because these were the first, some of the very first plants to occur on land. When plants and animals started to leave the oceans and come onto terrestrial environments and grow, this was among the first kinds of plants. And it was during that period, about 390 million years ago, this one existed here in Maine. And the plant was about a meter high. And you can see some kind of fruiting bodies, but you'll notice that there are no leaves on these plants. It's a very different kind of vegetative appearance.

And why is that? Well, let's take a look what environment that lived in. Here we are in a figure that goes back 600 million years, starts at 600 million years ago on the left. And the red line shows the amount of carbon dioxide in the atmosphere. And this was reconstructed by Robert Berner of Yale University about 20 years ago. It's a famous, in a famous paper. And what is interesting about it is today, compared to today's value, which is listed here as one, 20, about 600 million years ago, there was almost 20 times as much CO2 in the atmosphere as today. So there was an enormous amount more heat trapping capacity in the atmosphere, not 20 times as much heat was trapped. It doesn't work quite that way, but a lot more.

And that was the environment in which these early land plants were living in landscapes that are now Maine when they first came ashore. And it was a very warm, wet earth. And the reason it was warm, of course, was the trapping of the heat by the greenhouse gases, the CO2. But it was wet because the warmth of that climate caused a very great deal of evaporation from the world's oceans. The warmer the temperatures above the oceans, the more water is evaporated and the more water is carried on clouds over land. And so in those days, the environment was very moist.

And the early forests of the time included these, here's a rendition that shows tree ferns and a bunch of other things that were warm, swampy forests. There are often lots of water there. They were trees growing in these swampy wet conditions. And the trees would die, fall over, get buried. More trees grew there and fell over. And gradually, these big swampy areas became thick, woody peat bog-like things that eventually through time became crushed by sediments above and formed coal deposits on earth. These were the basic ingredients for coal.

And in fact, one of these plants that was shown in that last photo is an equizetum, or what we call horsetails commonly today. And these grow, I've seen them growing in California, but they grow all over the world. And they date back right to that 400 million year ago period. They're still there. In fact, this one species is indistinguishable as far as anybody can tell from one that was recognized in that 400 million year ago period. And so here's a relic of that time that still doesn't have many leaves, does it? It's quite interesting.

But as the climate, as these swampy forests grew and carbon was buried because of the death of the trees and the burial of more and more and more, and eventually sediments deposited on top of them, that was all removing carbon from the atmosphere. All the photosynthesis that went on by those plants was maintained in the material that was buried in those deposits that later became coal. And the marine equivalent of this, which were productive marine sediment, shallow marine systems where a lot of algae were growing and dropping into the sediments. And so a huge amount of carbon during that period was removed from the atmosphere as coal was formed, as oil and gas were deposited in shallow ocean sediments and as carbonate rocks were formed. And that's a part of the process I'm going to go into, but they're related.

And so as this process went on, the CO2 levels began to drop quickly during this period called the Carboniferous, which is of course given that name because that's when the carbon deposits, coal, oil and gas were formed and put under earth, you know, later on, retrieved by us for fuel. But one of the things that happened as the carbon dioxide levels fell so steeply during that Carboniferous period was the amount of CO2 in the atmosphere affected photosynthesis in the plants. And the surface areas of the spindly looking plants here on the left is that Pertica plant I showed you from the Maine fossil. And this is a schematic rendition of it, you could say.

But as the CO2 levels fell, plants evolved leaves. So there'd be greater surface area, so they could absorb the CO2 for photosynthesis. And as you know CO2 is a process taking CO2 from the atmosphere, water, usually up the stem from the ground, and then energy from the sun producing a sugar molecule and that's all that goes on. The leaves were formed so that the plants could have a greater surface area for collecting CO2 as the atmosphere had less of it to offer. And so as the CO2 levels fell on Berner's curve here, the leaves began to form and we see the plants we know today.

Now at the same time these early plants also had openings called stomata and you probably all remember these from biology class in high school or something if not more. But they're usually on the underside of leaves. There are these pairs of cells that can open and close and allow air to come, air to be exchanged from inside the plant and outside and it allows CO2 in and oxygen to go out and things like that and there are lots of adaptations for this depending on the aridity of the climate and so forth so we won't go into that.

But one of the interesting things about this is that people noticed early on and today that the density of stomata on the underside of the leaves is proportional to the amount of CO2. And in fact in herbarium specimens collected in England for example of certain tree species collected say in the 1700s when the CO2 levels were in the pre-industrial level, the density of stomata on the underside of the leaves was demonstrably greater than it is today. As the CO2 levels in the atmosphere have gone up, the plants don't need as many stomata to get enough CO2 and they've adapted so it's actually a way of almost predicting what the CO2 levels are once those are calibrated. So plants have very clever ways of adapting rather quickly actually to some of these changes even though the species aren't changing per se or anything but this is one of the many kinds of adaptations.

Well if we look at Berner's curve this is an interesting question. We know at the very end of this we had ice ages and I'll come back and talk more about ice ages in a minute, the quaternary ice ages that we looked at briefly. But what about back here when the CO2 levels at the end of the Carboniferous got down to modern levels why wouldn't there be ice ages then? Well turns out there were and it's just that simple. The laws of physics when there's a lot of CO2 in the atmosphere the earth is warmer, ice can't form when the earth is cold enough ice can form in the polar regions and so forth and we have ice ages. So there were ice ages 300 million years ago very similar to the one we're having now and we're in the middle of an ice age series.

Well this is a map, a polar map showing it's a schematic of course not a satellite but it's a map showing the amount of ice present in the northern hemisphere at the last glacial maxim and which was around 20,000 years ago and we can see that most of northern Europe and northern Asia and North America were covered. Greenland had more ice, Antarctica had more ice, the mountains in New Zealand and South America and so forth did as well. But this was how things were about 20,000 years ago but as the and this was an example of one of the ice age cycles that have gone on consistently actually for 2.6 million years.

What we call the Quaternary ice ages, Quaternary is a geologic time period that refers to the last 2.6 million years when we've had northern hemisphere ice ages on a regular basis. And this figure again shows the last 800,000 years and these high points, these brief high points on these curves are interglacial such as the warm one we're in now but they don't last, they didn't have never lasted very long more than 10 or 15,000 years and then the climate has cooled off and descended in about 80,000 years later to a glacial maximum and then suddenly the ice becomes unstable, the earth warms up quickly to another interglacial and this is part of the fascinating work that has brought us all into the science we're doing is to understand why these happen and I won't really go into it today but it is interesting.

And as the ice began to melt at the end of the last ice age, starting about 18,000 years ago, the ice quickly started to melt globally and peaks such as Katahdin, which is the highest mountain in Maine, it's about a mile high, would emerge from the ice and would have looked about like this, I actually took this photo in Antarctica but it looks very much like the top of Katahdin so it's a useful thing to show around here but then as the ice disappeared the landscape was covered by plants and animals and I'll show you a few examples of that in a minute but this present interglacial we're in, this warm period is known as the Holocene and now this new period of us having changed the Earth's atmosphere has now been termed by some people Anthropocene probably for a good reason but I just wanted to show that our species, homo sapiens, our ancestors of course go way back in evolutionary time to Central Africa several million years ago but our actual species by name has only been around less than two glacial cycles, we're just barely present here in this whole environment and although we're now doing quite a bit to change it so we're active parts of this system but this is a figure that's useful to see because the lower part of this, the blue part of this curve is the ice age cycles as recorded in the ocean sediments, I didn't talk much about how we know this but this comes from records that occur everywhere in the world's oceans and they're well understood and it's record of how much ice is on Earth and temperatures and things like that and you can see how well it matches the red curve above which is the CO2 in the atmosphere so those two are definitely linked and when the Earth is cold the CO2 levels are low when the Earth is warm CO2 levels are high and so forth the relationship is complicated a little bit and I won't go into that but it's clear that the laws of physics work in these ways.

Now we find out about what the environments of the recent past have been, the past few thousands of years by looking at lake sediments, this is my own, the part of my own research theme and this is a one meter long sediment from a lake up in Acadia National Park along the coast of Maine and this is a segment that's probably 2,000 to 2,500 years long, the amount of time represented in that one meter and it's brown mud consisting mostly of algal remains and remains of small animals that have lived in the lake but also contains a lot of pollen grains from plants that have lived in the landscapes around because pollen grains are released by many plants to blow on the wind and help fertilize flowers from their own species and because those are so abundant they, some of them end up being landing in the lake or washed into the lake and so we have a continuous record through time of the kinds of plants that live around that lake and part, most of my career was involved in studying environments and reconstructing past vegetation which gave us clues about past climate. These are pollen grains, photomicrographs of pollen grains of common tree species, they're actually quite beautiful and it's really a very peaceful meditative kind of thing to do to sit in a microscope for hours and hours as a student and count these.

Anybody who has the luxury of taking the time to do this is lucky because it's quite a beautiful thing. We prepare by taking a cubic centimeter of mud from that core that I just showed you. That cubic centimeter might have 50,000 pollen grains in it, so it's a huge sample statistically. We can process it chemically to get rid of the algal remains and things, but the pollen grains are made of very tough material that protects the inner cell contents. Those are preserved after we go through this preparation, and we can then microscopically identify each of these to the species they refer to.

Once we have done that for a given site and gotten radiocarbon dates to cross the ages of those sediments, and then when we've done that at many sites or hundreds of sites across the landscape, we can map out in space and time how the vegetation has changed in response to changing climate. This is a set of maps that I was able to publish with a couple of colleagues back in the late 1980s. They were quite the thing at the time because it was the first time we'd had a chance to see in one place the broad spatial patterns of change.

We can see here for three groups of trees in eastern North America - spruces, oaks, and pines - how their position on the landscape changed from 18,000 years ago, roughly as the ice started to melt, up to modern time. We can see how the spruces, the oaks, and also the pines formed their modern patterns, but through quite a diverse set of conditions. That has led to a lot of very interesting research going on.

Now I'd like to give you one quick tour through one of these examples just so you can get an idea of the dynamics of vegetation and the amount of change that takes place through time. This is a map drawn for 21,000 years ago, so this would be right at the last glacial maximum when the ice extent was its greatest, down here into central Iowa and places like that. You'll notice that the shape of Florida looks a little odd here, and it's not because of a lack of artistic skills on our part. It's that the sea level, the amount of ice locked up on land at the glacial maximum, was enough to reduce the sea level of the world's oceans by somewhere between 130 and 140 meters. That's how much water from the world's oceans was locked up on land.

As sea level fell by at least 120 or 130 meters, the continental shelves along places like the eastern coast of North America and around Florida and the Gulf Coast were exposed as dry land. There are fossils of mammoths and all kinds of trees and things out on those continental shelves dating back to the time when sea level was that much lower. Then gradually, as all this ice melted, sea level rose over top the continental shelves and the map started to look the way we expect it to now.

But what I'd like to do is go through this quickly in sort of a quick video format. You'll notice the names are up at the top left, not the name and the spruces and the age, but I'd like you to look down at the map and look at these green patterns. Green, the darker the green, that means the more density of that species, that the spruce is present at any given time. So here the spruce is living along the southern margin of that ice sheet. Spruces that now live way up in Maine and Canada.

I'll go through and I will say the times, and you just watch and try to keep track of watch for changes and try to look for times when things stay the same or are more dynamic or whatever. Just we'll roll through this and then talk about it. So 21,000, 19,000, 17,000, 15, 13, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, modern.

You'll notice that really there was no static time. Throughout this entire time, things were changing from thousand-year to thousand-year period. The spruce, the boreal forest patterns we see today in Maine and especially in Eastern Canada came into existence just in the last few thousand years. Four, five, six thousand years we start - I'll back up just a little bit so you can see that again. Let's back up to, let's say, eight thousand years ago, and you can see that whole boreal forest is - there's still a little bit of ice still left here actually at that time. But watch now: seven, you'll see the beginnings of the boreal forest as we know it today, six thousand, five thousand, four thousand, three thousand, two thousand, one thousand, today. And the southern margin of all this was moving to the south too as the climate got slightly cooler going into the warming we're experiencing now.

That's an important lesson here. We've learned this here and all over the world that what we recognize as the modern patterns of vegetation have only existed for about five or six thousand years. Prior to that, the organization, the particular communities that existed were in mixtures quite different from what we would recognize today. That's because the climates were different in significant ways. The seasonality of certain aspects of the climate, for example, were different enough in the summer and winter temperatures that different individual taxa of plants could grow together until they started to form to what we recognize in the last six or seven thousand years.

So I'll just summarize in a few points here some of these observations about the long-term responses, and we can talk more about these, but these are things that I think are interesting anyway and have some relevance to how we perceive what's going on in the natural world.

I just said that, told you, talked about this - that until the recent seven thousand years, we had different assemblages. We call them non-analogs from modern vegetation patterns. From what we know about the long-term records, this kind of reorganization of ecosystems that took place in the last 20,000 years had to have been going on throughout this entire 2.6 million years of the Quaternary ice ages. I say that because the same species are present in eastern North America, which is a relatively flat, level playing field you could say for the movement of changes in distribution and abundance of plants and animals.

The plants have adapted by moving around as ice sheets formed, as the climate got warmer and cooler, and each species had its own way of adapting. The climate envelope, you could say, for each of those - each species has its own unique one. That's why the mixtures could be different as the climates changed in their nature back through time. But the notion of all these ice ages going on for 2.6 million years, and yet all of these plants and animals still being here, suggests that this kind of reorganization I just showed you for the last 20,000 years has to have been going on through all those ice ages. All the plants and animals that are present somehow survive those, and we, as far as we know, these were all modern species. Everything about them is, as far as we can tell, they look the same. They're sort of probably certainly some minor differences in some physiology or something, but in everything we can tell about them, they're the modern species and not recognizably different. We only know of a few examples of plants that went extinct during that time, which is really interesting. I mean, until humans came along later on, because the extinctions about 12,000 years ago.

So that's an interesting point, that this reorganization is something that has been going on for that long through many ice age cycles. I think it's a really important property, ecological property of the system that we have here. Because if that's been going on for 2.6 million years, where species have been changing their distribution and abundance and which mixtures of things are growing together in a given place, that means nature is pretty resilient. That's a term we hear tossed around a lot, and people are thinking about it on these time scales, but I find it not only interesting but somewhat reassuring to know that the plants and animals, you know, left to themselves at least, can deal with quite severe changes in climate.

Now, there's - it still leaves the remaining question about the future though, doesn't it? Because I showed you that envelope of variability in the Earth's CO2 for the last 800,000, and it actually goes back several million years, but now we're outside that envelope. So what does that mean for when we see this kind of variability in the past, but suddenly now we're well beyond the variability of CO2 in the atmosphere for all that time? And none of the systems have been dealing with this kind of change, both the rapidity of the change and the scale, the actual nature of the change to warmer conditions, for at least several million years. So although I do appreciate the robustness of the system and the ecosystems' ability to reorganize during time, I think there are many unanswered questions about what might happen in the future as we proceed down this unintended experiment of changing the Earth's atmosphere so drastically.

Well, I'll end there and we'll talk about some questions, but I'd like to share some verses with you here. These are from William Blake's poem "Auguries of Innocence," which he apparently wrote in about 1803 but wasn't published until 60 years later or so. But these are the opening lines, and I like them:

"To see a World in a Grain of Sand

And a Heaven in a Wild Flower

Hold Infinity in the palm of your hand

And Eternity in an hour"

Now, I would actually substitute pollen, a grain of pollen, for a grain of sand in the upper line, and it would really suit me because when I look at pollen grains that I know are 17,000 years old, I feel like I hold eternity in my hand really and give and get insights about how the world has changed and how the world works. But I really love this opening to his poem, and it's an interesting poem. Some of you undoubtedly have studied it at some point and know a lot more about it than I, but essentially it is an appeal or a plea on his part for humans to be kinder and less cruel to nature and to plants and animals. It's very interesting that he wrote this in just after 1800 and was taking stock in how humans were treating our co-inhabitants of the Earth.

But I just thought this was an appropriate way to end, particularly with this group of you, and I'd be very happy to have questions and discussion. I can go back to slides if you'd like, but however you'd like to proceed is fine. I'm open to questions, discussion. I welcome any thoughts.