One pleasant June evening years ago, I took a break from ecological research at Isle Royale National Park and went canoeing in a large inlet named Washington Harbor, hoping to see some of the moose populating that isolated wilderness island in Lake Superior. Upstream, an old cedar arched gracefully over the waters, framing the forest and the deepening sky beyond.

The serenity and beauty of the scene rivaled the best of America’s landscape painting. For that moment, the remote island wilderness appeared as tranquil as a still-life, as permanent in form and structure as brush strokes on canvas at the Louvre.

Soon after I had pushed out from shore, a large bull moose stepped carefully into the cold lake waters and began a slow traverse of the shallows, searching for water irises, lilies and other water plants that were some of his favorite summer foods. He circled the shallows for 20 minutes, rarely stopping to feed. In this northern wilderness, June was too early for water plants, and as the moose edged his way over to the north shore, he found little to eat. Suddenly, he galloped through the shallows, scrambled out of the inlet, and began kicking vigorously at the shore. He dashed up a short bluff, breathing rapidly, turned, raced down and kicked again where the sand and waters met. It was as if he were furious with the harbor for denying him food, but I never did understand why he acted that way.

Nothing could have contrasted more with the idyllic scenery of that evening than the moose’s bizarre, chaotic and perplexing behavior. But in the almost half-century that I have studied nature’s character, I have come to realize that the seeming constancy of the harbor symbolized a false myth about nature, while the moose that kicked at the shore—complex, changeable, hard to explain, but intriguing and appealing in its individuality—was closer to the true character of biological nature, with its complex interplays of life and physical environment on our planet.

With the Copenhagen climate conference drawing to a close, and the perhaps-compromised science of global warming everywhere in the news, the big bull moose came to mind as a reminder of the difference between the way much of environmental science has been approached and the way nature actually works.

Most of the major forecasting tools used in global-warming research, including the global climate models (known as general circulation models of the atmosphere) and those used to forecast possible ecological effects of global warming, paint a picture of nature more like a Hudson River School still-life than like the moose that kicked at the shore. These forecasting methods assume that nature undisturbed by people is in a steady state, that there is a balance of nature, and that warnings the climate is at a tipping point mean that the system is about to lose its balance.

In fact, however, nature has never been constant. It is always changing, and life on Earth has evolved and adapted to those changes. Indeed many species, if not most, require change to persist. So there is something fundamentally wrong in most approaches to forecasting what might happen if the climate warms. The paradigm is wrong and has to change. But such fundamental change in human ideas never comes easily, and it is often resisted by those whose careers have been based on the old way of thinking. In addition, the general circulation models are such complex computer programs, and have been developed over so many years, that a fundamental change in the entire way of thinking about climate dynamics and its ecological implications is all the more difficult.

The recently revealed emails from the East Anglia Climate Research Unit, better known as “Climategate,” illustrates the difficulty of letting go of old, perhaps flawed methods. We who work in environmental sciences and on global warming need to open ourselves to a much greater variety of ways of thinking about nature. We need to develop forecasting methods that are appropriate for always-changing, non-steady-state systems where chance— randomness—is inherent.

Among the various things I have tried over the course of four decades of work on the effects of global warming were a few computer models of the carbon-dioxide cycle, small computer programs, taking quite different approaches than the standard at the time to the question of what might happen if carbon dioxide were to increase rapidly from human actions. I created a strange little model of little boxes, each representing what we ecologists call “biomes”—major ecosystems on Earth, like all tropical forests. These “competed,” so to speak, for CO2 in the atmosphere through their photosynthetic organisms, and returned some of that CO2 back to the atmosphere as the model’s “creatures” respired or died and decayed.

The results were as strange and surprising to me as the moose who kicked at the shore. The CO2 in the atmosphere didn’t just build up over hundreds of years and then slowly decline to the same perfect equilibrium concentration in the Earth’s atmosphere prior to the industrial age. No, instead it oscillated strangely, because the biome that had the fastest rate of uptake “out-competed” the others, pulling the CO2 concentration down so far that the plants and algae in other biomes didn’t have enough and died back, giving up their stored CO2 to the atmosphere.

That strange little computer model was at the time just as ephemeral for me as that evening canoe ride at Isle Royale. It got me thinking about how a complicated, intricate, always-changing system could respond to a novel input. The computer, caring even less about me than did the bull moose, simply showed me exactly what the consequences of my assumptions were.

I didn’t publish that work because it was so simple, yet different, and seemed more a personal insight than a definitive forecast. But looking back now at the bull moose and that little computer model, I believe that we have been on the wrong path in our view of the way nature works, and we need a fundamental change in our paradigm.

This can come about only in an intellectual atmosphere that is open, free, and wildly experimental. It would be an atmosphere that let us accept that natural ecological systems are likely to be full of surprises, like a moose kicking at the shore.

And once we open ourselves to those possibilities, perhaps we won’t find ourselves caught between defending weak science or lashing out, like that bull moose, and kicking at what seems to stand in our way.

Originally published in the Wall Street Journal, December 19, 2009.

One of the changes among scientists in this century is the increasing number who believe that one can have complete and certain knowledge. For example, Michael J. Mumma, a NASA senior scientist who has led teams searching for evidence of life on Mars, was quoted in the New York Times as saying, “Based on evidence, what we do have is, unequivocally, the conditions for the emergence of life were present on Mars—period, end of story.”

This belief in absolute certainty is fundamentally what has bothered me about the scientific debate over global warming in the 21st century, and I am hoping it will not characterize the discussions at the United Nations Climate Change Conference in Durban, South Africa, currently under way.

Reading Mr. Mumma’s statement, I thought immediately of physicist Niels Bohr, a Nobel laureate, who said, “Anyone who is not shocked by quantum theory has not understood it.” To which Richard Feynman, another famous physicist and Nobel laureate, quipped, “Nobody understands quantum mechanics.”

I felt nostalgic for those times when even the greatest scientific minds admitted limits to what they knew. And when they recognized well that the key to the scientific method is that it is a way of knowing in which you can never completely prove that something is absolutely true. Instead, the important idea about the method is that any statement, to be scientific, must be open to disproof, and a way of knowing how to disprove it exists.

Therefore, “Period, end of story” is something a scientist can say—but it isn’t science.

I was one of many scientists on several panels in the 1970s who reviewed the results from the Viking Landers on Mars, the ones that were supposed to conduct experiments that would help determine whether there was or wasn’t life on that planet. I don’t remember anybody on those panels talking in terms of absolute certainty. Instead, the discussions were about what the evidence did and did not suggest, and what might be disprovable from them and from future landers.

I was also one of a small number of scientists—mainly ecologists, climatologists and meteorologists—who in the 1970s became concerned about the possibility of a human-induced global warming, based on then-new measurements. It seemed to be an important scientific problem, both as part of the beginning of a new science of global ecology and as a potentially major practical problem that nations would have to deal with. It did not seem to be something that should or would rise above standard science and become something that one had to choose sides in. But that’s what has happened.

Some scientists make “period, end of story” claims that human-induced global warming definitely, absolutely either is or isn’t happening. For me, the extreme limit of this attitude was expressed by economist Paul Krugman, also a Nobel laureate, who wrote in his New York Times column in June, “Betraying the Planet” that “as I watched the deniers make their arguments, I couldn’t help thinking that I was watching a form of treason—treason against the planet.” What had begun as a true scientific question with possibly major practical implications had become accepted as an infallible belief (or if you’re on the other side, an infallible disbelief), and any further questions were met, Joe-McCarthy style, “with me or agin me.”

Not only is it poor science to claim absolute truth, but it also leads to the kind of destructive and distrustful debate we’ve had in last decade about global warming. The history of science and technology suggests that such absolutism on both sides of a scientific debate doesn’t often lead to practical solutions.

It is helpful to go back to the work of the Wright brothers, whose invention of a true heavier-than-air flying machine was one kind of precursor to the Mars Landers. They basically invented aeronautical science and engineering, developed methods to test their hypotheses, and carefully worked their way through a combination of theory and experimentation. The plane that flew at Kill Devil Hill, a North Carolina dune, did not come out of true believers or absolute assertions, but out of good science and technological development.

Let us hope that discussions about global warming can be more like the debates between those two brothers than between those who absolutely, completely agree with Paul Krugman and those who absolutely, completely disagree with him. How about a little agnosticism in our scientific assertions—and even, as with Richard Feynman, a little sense of humor so that we can laugh at our errors and move on? We should all remember that Feynman also said, “If you think that science is certain—well that’s just an error on your part.”

This op-ed appeared in the Wall Street Journal on December 2, 2011

Ironies of the Information Age

During the time  that I have been an ecological scientist and involved with environmental issues, I have found several ironies of our modern technological and scientific information age. The first irony is that often we do not measure what we need to know. I have been involved in a lot of major environmental issues, from the conservation of bowhead and sperm whales to the possible effects of global warming on forests. In each case I find that there are key pieces of information missing that nobody has bothered to find out.

The second irony of the information age thing is that, if we do measure something useful, we usually don’t bother to use it. This is true among scientists as well as among public agencies and non-profit interest groups. We just archive information and forget it.

The third irony that, although we have the ability to gather many kinds of scientific information, we tend to solve environmental problems from ancient myths, plausibilities, false inferences, and ideologies. This means we often start with an answer that we wish were true and squeeze whatever scientific information we use into a mold that conforms to this wish. And we get very upset if people do not believe us.
Thoreau as a Seeker of Quantitative Information

Here Thoreau is a wonderful example to us. Thoreau buffs are familiar with his search for quantitative measurements, his careful analysis of information, and how his imagination was stimulated by what he learned. His experience that strikes me the strongest is his measurement of the depth of Walden Pond.

“There have been many stories about the bottom, or rather no bottom, of this pond, which certainly had no foundation for themselves,” Thoreau punned in Walden. “It is remarkable how long men will believe in the bottomlessness of a pond without taking the trouble to sound it.”‘ He went on to write that “Many have believed that Walden reached quite through to the other side of the globe” (285). And so he became interested in the depth of the pond and set out to learn this physical, quantitative characteristic of one of his favorite places in nature.

As a person with an intrinsic naturalist’s and observer’s inclination, Thoreau took a simple and direct approach to determining the depth of the pond: he measured it. He had the skill to do this, because he often worked as a surveyor. “As I was desirous to recover the long lost bottom of Walden Pond,” he wrote, “I surveyed it carefully, before the ice broke up early in ’46 with compass and chain and sounding line. I fathomed it easily with a cod-line and a stone weighing about a pound and a half, and could tell accurately when the stone left the bottom, by having to pull so much harder before the water got underneath to help me” (285-287). Thoreau made an important step from informal natural history to quantitative measurement. This is a key step in using science to obtain a new kind of understanding of nature.

Once he had made one measurement. his curiosity was aroused and he began to investigate the general shape of the pond’s basin. He made more than one hundred measurements of the pond’s depth. From these he made a map, using his skills as a surveyor, and located the deepest point in the pond: “The greatest depth was exactly one hundred and two feet; to which may be added the five feet which it has risen since [with the spring runoff into the pond], making one hundred and seven” (237).

His curiosity further aroused, Thoreau began to consider generalizations arising from his quantitative measurements. “As I sounded through the ice I could determine the shape of the bottom with greater accuracy than is possible in surveying harbors which do not freeze over, ” he wrote (288).

Measurements led to surprises. “I was surprised at its general regularity,” he wrote. “In the deepest part there are several acres more level than almost any field which is exposed to the sun, wind and plough. In one instance, on a line arbitrarily chosen, the depth did not vary more than one foot in thirty rods; and generally, near the middle, I could calculate the variation for each one hundred feet in any direction beforehand within three or four inches. Some are accustomed to speak of deep and dangerous holes even in quiet sandy ponds like this, but the effect of water under these circumstances is to level all inequalities” (288-289).

Thoreau’s investigation then went through a progression to ever more general theoretical constructs, leading to the development of a set of hypotheses about ponds and lakes in general. To do this, he had to find a means to aggregate his data so that Thoreau could see the result as a whole and think about that whole. For him, with his experience as a surveyor. this was the straightforward step of making a map. This required that his depth soundings be located geographically.

From the map he “observed a remarkable coincidence,” he wrote, “the line of greatest length intersected the line of greatest breadth exactly at the point of greatest depth” (289). Now Thoreau had expanded his inquiry beyond the initial question of the depth of the pond. Having done a series of measurements, he began to see the pond differently, as if its bottom were a field, and he became curious about the shape of that field. Measurements had touched his imagination.

In reelecting on possible generalizations about his observations, Thoreau considered a comment made by somebody whose opinion he respected. “A factory owner hearing what depth I had found,” he wrote, “thought that it could not be true, for, judging from his acquaintance with dams, sand would not lie at so steep an angle” (287). In this process Thoreau was not the mythical hermit avoiding human contact, but a person who considered the judgment of others when their experience and knowledge might seem valuable.

At this point he was beginning to move into an interesting thought process. A simple curiosity had led to a simple measurement, then to a series of those measurements, which had then led him to a consideration of whether the measurements could be correct and, if so, what they implied. Here, it implied that ponds could not simply always be shaped along the edges like dams of sand. “But the deepest ponds are not so deep in proportion to their area as most suppose,” Thoreau continued, “and, if drained, would not leave very remarkable valleys. They are not like cups between the hills: for this one, which is so unusually deep for its area, appears in a vertical section through its centre not deeper than a shallow plate. Most ponds, emptied, would leave a meadow no more hollow than we frequently see” (287)

Based on his series of quantitative measurements, Thoreau began to speculate about the shape of ponds in general. He began to develop a hypothesis: perhaps the greatest depth of all ponds would tend to occur at the intersection of the line of greatest width and the line of greatest length. To test this idea, quantitative measurements were necessary. His scientific measurements piqued new curiosity, led to new kinds of questions, while leading to a new understanding. The new understanding brought him, in a different way than before, closer to nature.

Thoreau’s study of the pond brings out another important distinction, that between observations and inferences, which are ideas that are developed based on a set of observations. A casual observation that Walden Pond looks deep is one thing, an inference from a single glance that it must be deep everywhere is another — it is a false inference. Confusing observations with inferences and accepting untested inferences is the kind of sloppy thinking often described by the phrase “thinking makes it so,” and is something that continues to pose problems for dealing with nature and the environment.2

Applying Thoreau’s Approach To Modern Environmental Issues

One would hope that this sound, fundamental scientific approach would be followed today. After all, it’s been well known and well applied for several centuries. And one would hope it was applied to modem issues about nature – the very object to which Thoreau himself applied the method.

But sad to say, I have found over and over again that today’s environmental issues often receive as much scientific analysis as the people who chose to sit by Walden Pond and guess at its depth.

Wherever possible, Thoreau tried to learn directly for himself. In general, he did not accept at face value what other people said. Perhaps the greatest example of this is his experience with his mentor, Emerson. As part of Transcendentalism, Emerson believed that nature was benign and cared about human beings. Thoreau listened to the great man and then went to the Maine woods where he climbed Mount Katahdin to see if this were true for nature at her rawest. He found that it was not true, at least not for himself.

When a subject came up that he could not answer in such a direct manner by himself, Thoreau sought experts, and he used expertise in a specific way. Once again, his approach is useful to us. Our society is confused about experts, especially scientific experts – about who is a scientific expert and about the role of scientists and science within our society. When Thoreau could not answer a question directly, he sought people who had had direct experience with the subject that concerned him. In his travels through the Maine woods, he was impressed by Joe Polis, his last guide there, and sought to understand how Polis could find his way so well in the forests.

But even with experts, Thoreau was cautious. He used the assertions of experts as hypotheses to be tested, as the beginning of exploration, not the end. This happened when he visited Cape Cod. There he learned that the Cape itself – its soils, it shape – was continually changing under the force of winds and water. He learned that first from the Wellfleet Oysterman and from other long-term residents of the Cape. One “told us that a log canoe known to have been buried many years before on the Bay side at East Harbor in Truro, where the Cape is extremely narrow, appeared at length on the Atlantic side, the Cape having rolled over it, and an old woman said – ‘Now, you see, it is true what I told you, that the Cape is moving.’

Then he sought out the keeper of Highland Lighthouse, who he learned had lived there for many decades. The Highland Light was a landmark then as it is today, a classic white pillar rising above a white building on the edge of a picturesque dune, high above the beach and the water, facing to the east, to the open Atlantic ocean. It sits on the edge of an undulating landscape of dune grass, shrubs, small oaks and pitch pines, a mixture of patches of grasslands, shrub lands, and salt-spray-stunted, open woodlands. It is a lonely but picturesque landscape. The lighthouse stands on the edge of huge dunes that afford a grand view of the shore below. From the lighthouse, the dune falls away steeply for a long distance. Far below, at the base of the dune on which the lighthouse sits, people strolling along the strand appear as tiny toy figures.

The Lighthouse was built in 1798 to provide one of the major lights to guide ships away from dangerous shoals along the coast of the Cape, and it performed that function during Thoreau’s time. Today, the lighthouse is automated and no longer has a keeper.  The Lighthouse Keeper that Thoreau met agreed about the movement of the Cape. “According to the light-house keeper, the Cape is wasting here on both sides, though most on the eastern,” Thoreau wrote (118). Thoreau listened, was intrigued by this hypothesis, and then constructed some surveying equipment from materials he borrowed from a carpenter, and made his own measurements. “I borrowed the plane and square, level and dividers, of a carpenter who was shingling a barn near by,” Thoreau wrote, “and using one of those shingles made of a mast, contrived a rude sort of quadrant, with pins for sights and pivots, and got the angle of elevation of the Bank opposite the light-house, and with a couple of cod-lines the length of its slope, and so measured its height on the shingle” He observed that the dune rose 110 feet “above its immediate base” and 123 feet above mean low tide.

Next, he checked his measurements against those of other land surveyors. “Graham, who has carefully surveyed the extremity of the Cape, makes it one hundred and thirty feet,” he wrote (118). Then he looked for signs of erosion — making qualitative observations. He found evidence of erosion about a half mile south of the lighthouse, at the point of highest land in the vicinity. There along the dune he saw streams “trickling down it at intervals of two or three rods” which left erosional shapes like “steep Gothic roofs fifty feet high or more,” which were at one location “curiously eaten out in the form of a large semicircular crater” (118).

Still not content with the opinion of the lighthouse keeper nor the measurements he was able to take himself, he examined data kept by the lighthouse keeper. “We calculated, from his data, how soon the Cape would be quite worn away,” Thoreau wrote (118-119, emphasis Thoreau’s). Thoreau made additional measurements when he returned to the Cape the following summer. “Between this October and June of the next year I found that the bank had lost about forty feet in one place, opposite the light-house,” he wrote (119). From these observations he concluded that the Cape was wearing away about six feet a year. But he was cautious about simple extrapolation and generalization from a few observations. “Any conclusion drawn from the observations of a few years or one generation only are likely to prove false,” he wrote, “and the Cape may balk expectation by its durability.” This skepticism — even about one’s own measurements and observations   is one of the important features of science and of scientists.

The steps are clear: first, learn for yourself if at all possible; second, if not, select your experts carefully – make sure they have had direct experience; third, listen to what they say and treat that as a hypothesis; fourth, test the hypothesis for yourself.

This is the path to knowledge we followed with Jim Welter. We viewed his graphs of salmon and water flow, and then made extensive statistical analyses to see if what looked to be the case held up under analysis. It did.

This way of selecting experts and using their knowledge was useful in our situation and can he useful today. It is not the role of scientists, as experts, to make policy, but to advise us about what is possible based on their knowledge and about how we can achieve the choices of the possible, what we gain and what we give up. Then in a democratic society it is up to us to decide which of the possible choices we wish to pursue.

Encompassing all these specific ways that Thoreau’s life and writings can be of direct use to us in solving our environmental problems is his love of nature and his life-long search for ways to combine both a physical scientific and a spiritual contact with nature. These, and his love of learning and of civilization, are guides to us for today and the future as we struggle to find how we can conserve our surroundings and maintain the best that human civilization can offer.

Notes

1 Thoreau, Henry David. Walden. J. Lyndon Shanley. ed.. Princeton, N.J.: Princeton University Press, 1971, 285.

2 In this discussion of the scientific method I am indebted to Dorothy Rosenthal, who wrote chapter 2 in Botkin, D. B. and E. A. Keller, Environmental Science: The Earth as a Living Planet . Third Edition. New York: John Wiley and Sons, 1999.

3 Thoreau, Henry David. Cape Cod. Joseph J. Moldenhauer, ed. Princeton, N.J.: Princeton University Press, 1988, 120-121.

4  The original talk was published as Botkin, D. B., 2001, “The Depth of Walden Pond: Thoreau as a Guide to Solving Twenty-first Century Environmental Problems,” The Concord Saunterer N. S. 9: 5-14.

In all of this work, my goal was to do an objective scientific analysis and new research, following traditional scientific principles of disprovability. This research includes observations (empirical studies) and theory. Wherever possible, theoretical models have been tested and validated.

Now that global warming has become a major public issue, a great many people are speaking and writing about global warming , regardless of their knowledge, experience, research, and study of the subject. As a result, people have been asking me a variety of questions about the scientific basis of what we are being told.

Ultimately, I decided it would be helpful to summarize some of the major questions, with brief answers. To assure the reader that I have done years of research on this subject, I have also listed my major papers that deal directly with ecological effects of global warming or provide some scientific results essential to assessing some of its possible ecological effects. That list follows the 21 questions and answers.

One of the reasons that debates over global warming become confused is that the subject raises a number of scientific questions and as a result people often talk at cross-purposes. Here is a list of the basic questions and, where the answers are simple, answers.

Questions about Global Warming Itself

1. Is there a greenhouse effect?
Yes, some gases and liquids transmit visible light and absorb infrared light.

2. What are the major greenhouse gases in our atmosphere?
Water vapor, carbon dioxide, methane, nitrogen oxides, and CFCs (Freon). Strictly speaking, water vapor is the major greenhouse gas by concentration; the rest are minor constituents of the atmosphere.

3. If carbon dioxide is only 0.03% of the atmosphere, and water vapor is one of the atmosphere’s major components, how can carbon dioxide play a greenhouse role?
The answer has to do with the infrared wavelengths carbon dioxide absorbs uniquely and the fact that it liquefies and freezes at a lower temperature than water does and therefore can act as a greenhouse gas much higher in the atmosphere than water can.

4. Has the climate changed in the past prior to the industrial age and prior to any human effects on the atmosphere? If so, at rates and degrees that are forecast by current climate models to happen in the near future for us?
Yes, recent scientific evidence indicates that climate has always been changing, and prior to human influences, temperature has changed as rapidly and to as great a degree as is forecast to occur in the future from the global warming computer models.

5. Is carbon dioxide increasing?
Yes. There are solid data for this.

6. Are any of the other greenhouse gases increasing?
Data support that this is happening for methane, nitrogen oxides, and CFCs. It is worth noting that rate of increase in methane, CFC-11, and CFC-12 slowed (or even decreased) recently, for reasons that are not well explained or understood.

7. Has the temperature been rising steadily in recent years?
There have been decades in the 20th century when the temperature rose and decades when it fell. Up through the end of the 1990s, there had been a recent warming trend. So far, it is unclear whether this is continuing in the 21st century. A warming trend began around 1850, lasting until the1940s, when temperatures began to cool again, followed by a leveling off of temperature in the 1950s, and a further drop during the 1960s. After that, the average surface temperature rose.

8. What is the source of the major beliefs that global warming will occur and will have severe and undesirable effects?
Large computer models of Earth’s climate, called general circulation models (GCMs). There are at least 30 of these in use worldwide.

9. Have these climate models been proved to be true?
Scientists refer to such proof as model validation. The GCMs have not been validated with standard scientific methods.

10. Are there any legitimate questions about the forecasts from these climate models?
Yes. In particular: Climate modelers and their critics agree that the models do not do a very good job with water in the atmosphere. As the climate warms, more water is evaporated from Earth’s surface. A key question is: Does most of this water remain vapor (a greenhouse gas) or condense into clouds (that cool the climate)?

1. The models are steady-state, requiring and assuming that a specific change in the concentration of a greenhouse gas always has the same effect, regardless of past changes and total concentration. In fact, however, climate is always changing and is not in a steady state.
2. The effect on climate of carbon dioxide and other greenhouse gases is not linear. As the concentration of carbon dioxide goes up, an increase in a ton of CO2 has less and less effect on climate.
3. The relative effects of greenhouse gases compared to other factors that influence the Earth’s temperature are still open to debate. Among these other factors are the following:
   1. variations in the sun’s energy output;
   2. internal dynamics of the atmosphere, ocean, and life, which can modulate the direct greenhouse effects.
4. One of the main causes of variation in sunlight reaching the Earth is long-term variations in our planet’s path around the sun and its tilt and wobble as it spins like a top. Known as the Milankovitch cycles, these produce variations over 20,000, 40,000, and 100,000 years and are believed to be the primary drivers of the glacial and interglacial cycles.
5. The models are weak in their handling of the dynamics of land vegetation and ocean dynamics, and the coupling among these and the dynamics of the atmosphere. Since both oceans and land vegetation — especially forests, wetlands, and grasslands — can have major effects on atmospheric chemistry and physics, these aspects of the global models need considerable attention.

Questions about Possible Effects of Global Warming

11. The UN IPCC report states that up to 30% of animal and plant species will be threatened with extinction in the next few decades from global warming. Is this realistic?
In the past 2½ million years, under climate change as great and as fast, very few animal and plant species went extinct, far less than 30%. Most forecasting methods suggest that extinctions will be fewer than the IPCC asserts. Methods that suggest high rates of extinction assume that the world is in steady state and must be in steady state for species to persist; that species have little or no ability to adjust and adapt to climate change, contrary to well-established biological and ecological knowledge.

12. Will tropical epidemic diseases spread widely and rapidly?
Some excellent scientific papers show that temperature is not a good basis to forecast the spread of malaria and encephalitis. In fact, until the second half of the 20th century, malaria was endemic and widespread in many temperate regions and there were epidemics north to the Arctic Circle.

13. Will all the ice in the arctic melt?
Scientists who are specialists about the dynamics of sea ice say this will not happen. What might happen is that the Northwest Passage could open up – could become ice-free – for a few months in the summer; large areas of sea ice in the arctic might melt back, but these would be renewed each year. Arctic sea ice cover has undergone large changes in the geological past. For example, studies of deposits of fossil plankton indicate that sea ice in the Chukchi Sea was significantly less between 6,000 and 2,500 years ago. (These organisms respond rapidly to climate change.)

14. Will many arctic mammals go extinct from this change in ice cover?
Today’s arctic mammals evolved long enough ago for the species to have experienced past climate changes of equal rate and amount, and survived these. Experts on arctic mammals are concerned about a few that have very specific requirements and narrow, highly specialized ecological niches.

15. What about polar bears?
There are between 17,000 and 27,000 polar bears worldwide, and some of the populations have increased recently. Polar bears evolved several hundred thousand years ago and survived past climate changes equal in rate and amount to what is forecast to happen in the future. Ecologists and geneticists have in the past said that a species is not likely to be threatened with extinction until its number gets below 500 individuals.

16. Are all mountain glaciers melting because of present warming?
No. A prime example is Mt. Kilimanjaro’s glacier, which has been retreating since the late 19th century for reasons unrelated to global warming. Some mountain glaciers may retreat from global warming, but this can happen only when the temperature at the elevation of the glaciers is above freezing, or if global warming greatly reduces snowfall in those mountains.

17. Is Greenland’s ice melting? If so, will it disappear?
Current scientific papers disagree about the extent to which Greenland has lost its glacial ice in recent years and about how much the glaciers will change in the future. But the most thorough recent study by Greenland scientists suggests that Greenland’s glaciers have oscillated and are not in general decreasing.

18. Is the sea level rising rapidly because of global warming?
The sea level has been rising at about a 18 cm (7 inches) a century since the end of the last ice age. Between 1993 and 2003, the sea level rose about 3.1mm/year, or a rate of 31 cm (about 1 foot) a century. There is much disagreement about what may happen to the sea level in the future, even among climatologists and oceanographers, and even if global warming happens as forecast by the global climate models.

19. Will some island nations disappear due to sea-level rise?
Yes, even from the background rate (the rate at which the sea level has been rising without global warming). But the jury is still out as to whether the sea level is rising more rapidly than that, and therefore might be causing accelerated problems of this kind. (Of course, healthy coral reefs grow and in the past have kept pace with sea level rise.)

20. Will global warming affect world food production?
If global warming occurs, it will change where the best areas for agriculture will be. Present forecasting methods are not good enough to tell us much more than that. The result will be that some countries will benefit and others will lose agriculture production.

21. Are there any fundamental underlying issues we have not addressed?
One of the most important is whether, globally, life and its life-supporting systems have been, must be, and are best in a steady state, one that is unchanging over time. The most extreme concerns about global warming assume that life and its environment must remain as they were around 1960. This assumption is common among climatologists who argue that global warming is happening and will be disastrous. In contrast, ecologists have established that ecological systems are not steady-state and that species not only have evolved and adapted to change, but in fact many, perhaps most, require change.

Global warming Publications by Daniel B. Botkin

Books

1. Botkin, D.B., and E.A. Keller, 1987, Environmental Studies: Earth as a Living Planet (Columbus, Ohio: Charles E. Merrill), 500 pp. (2nd edition; 1st edition published 1982).

2. Botkin, D.B., M. Caswell, J.E. Estes, and A. Orio, eds., 1989, Changing the Global Environment: Perspectives on Human Involvement (New York: Academic Press).

3. Botkin, D.B., 1990, Discordant Harmonies: A New Ecology for the 21st Century (New York: Oxford University Press).

4. Botkin, D.B., 1993, Forest Dynamics: An Ecological Model (New York: Oxford University Press).

5. Skinner, B., S. Porter, and D.B. Botkin, 1999, The Blue Planet (New York: John Wiley & Sons).

6. Botkin, D. B., and E.A. Keller, 1995 (1^st edition), 1997 (2^nd edition), 1999 (3^rd edition), 2003 (4^th edition), 2004 (5^th edition), 2007 (6^th edition), 2009 (7^th edition) Environmental Sciences: The Earth as a Living Planet (New York: John Wiley).

7. Keller, E.A., and D.B. Botkin, 2007, Essential Environmental Science (New York: John Wiley).

Global Warming Articles and Reports by Daniel B. Botkin

1. Botkin, D.B., J.F. Janak, and J.R. Wallis, 1973, Estimating the effects of carbon fertilization on forest composition by ecosystem simulation, pp. 328-344, In G.M. Woodwell and E.V. Pecan, eds., Carbon and the Biosphere, Brookhaven National Laboratory Symposium No. 24, Technical Information Center, U.S.A.E.C., Oak Ridge, TN.

2. Botkin, D.B., 1977, Forests, lakes, and the anthropogenic production of carbon dioxide, BioScience 27: 325-33

3. Woodwell, G.M., R.H. Whittaker, W.A. Reiners, G.E. Likens, C.A.S. Hall, C.C. Delwiche, and D.B. Botkin, 1978, The biota and the world carbon budget, Science 199: 141-146.

4. Ralston, Charles W., G.M. Woodwell, R.H. Whittaker, W.A. Reiners, G.E. Likens, C.C. Delwiche, D.B. Botkin, 1979, Where Has All the Carbon Gone? Science, New Series, Vol. 204, No. 4399. (Jun. 22, 1979), pp. 1345-1346.

5. Botkin, D.B.,ed., 1980, Life from a Planetary Perspective: Fundamental Issues in Global Ecology. Final report NASA Grant NASW-3392. 49 pp.

6. Botkin, D.B., 1982, Can there be a theory of global ecology? Journal of Theoretical Biology, 96: 95-98.

7. Botkin, D.B., 1984, The Biosphere: The New Aerospace Engineering Challenge. Aerospace America, July 1984, pp. 73-75.

8. Botkin, D.B., J.E. Estes, R.M. MacDonald, M.V. Wilson, 1984, Studying the Earth’s Vegetation from Space, BioScience 34(8):508-514.

9. Botkin, D.B., and S.W. Running, 1984, Role of Vegetation in the Biosphere, Purdue University Machine Processing of Remotely Sensed Data (Symposium), pp. 326-332.

10. Davis, M.B., and D.B. Botkin, 1985, Sensitivity of the Cool-Temperate Forests and Their Fossil Pollen to Rapid Climatic Change, Quaternary Research 23:327-340.

11. Botkin, D.B., 1985, The Need for a Science of the Biosphere, Interdisciplinary Science Reviews,10(3):267-278.

12. Botkin, D.B., 1985, The Science of the Biosphere, Origin of Life, 15:319-325.

13. Orio, A.A., and D.B. Botkin, eds.,1986, Man’s Role in Changing the Global Environment, Proceedings of International Conference, Venice, Italy, 21-26 October 1985; The Science of the Total Environment 55: 1-399 and 56:1-415.

14. Bretherton, F.P., D.J. Baker, D.B.Botkin, K.C.A. Burke, M. Chahine, J.A. Dutton, L.A. Fisk, N.W.Hinners, D.A. Landgrebe, J.J. McCarthy, B. Moore, R.G. Prinn, C.B. Raleight, WV.H.Reis, W.F. Wee,s, P.J. Zinke, 1986, Earth Systems Science: A Program for Global Change, NASA Earth Systems Science Committee of the NASA Advisory Council, Washington, DC. 48pp + supplements.

15. Botkin, D.B. 1986, ed., Remote Sensing of the Biosphere, National Academy of Sciences, Washington, DC.

16. Botkin, D.B., 1989, “Science and The Global Environment,” pp. 3-14 (Chapter 1) in Botkin, D.B., M. Caswell, J.E.Estes, A.Orio, eds., Man’s Role in Changing the Global Environment: Perspectives on Human Involvement (Boston: Academic Press).

17. Stolz, J.F., D.B. Botkin, and M.N.Dastoor, 1989, “The Integral Biosphere”, pp. 31-49 (Chapter 3) in M.B. Rambler and L. Margulis, eds., Global Ecology:Towards a Science of the Biosphere (Boston: Academic Press).

18. Botkin, D.B., R.A. Nisbet, and T.E. Reynales, 1989, “Effects of Climate Change on Forests of the Great Lake States, pp.22-31 in The Potential Effects of Global Climate Change on the United States, J.B. Smith and D.A. Tirpak, eds. U.S. Environmental Protection Agency, Washington, DC, EPA -203-05-89-0.

19. Rosenfeld, A.H., and D.B. Botkin, 1990, Trees Can Sequester Carbon, Or Die, Decay, and Amplify Global Warming: Possible Positive Feedback Between Rising Temperature, Stressed Forests, and CO₂, Physics and Society 19:4pp.

20. Botkin, D.B., and L. Simpson, 1990, Biomass of the North American Boreal Forest: A step Toward Accurate Global Measures: Biogeochemistry 9:161-174.

21. Botkin, D.B., and L.G. Simpson, 1990, Distribution of Biomass in the North American Boreal Forest, pp. 1036-1045 in G. Lund, ed. Proceedings of the International Conference on Global Natural Resource Monitoring and Assessments: Preparing for the 21st Century, American Society for Photogrammetry and Remote Sensing.

22. Botkin, D.B., and R.A. Nisbet, 1990, Response of Forests to Global Warming and CO₂ Fertilization, Report to EPA.

23. Botkin, D.B., D.A. Woodby, and R.A. Nisbet, 1991, Kirtland’s Warbler Habitats: A Possible Early Indicator of Climatic Warming, Biological Conservation 56 (1): 63-78.

24. Botkin, D.B., 1991, Global Warming and Forests of the Great Lakes States: An Example of the Use of Quantitative Projections in Policy Analysis. An Essay submitted for the George and Cynthia Mitchell International Prize Competition, 1991, which won first prize and was published by the Mitchell Foundation, Houston, TX.

25. Botkin, D. B., 1991, Global Warming: What it is, What is Controversial About it, and What We Might Do In Response To It, UCLA J. of Environmental Law and Policy, 9: 119-142.

26. Botkin, D.B., R.A. Nisbet, S. Bicknell, C. Woodhouse, B. Bentley, and W. Ferren, 1991, Global Climate Change and California’s Natural Ecosystems, pp. 123-149 in J.B. Knox, ed., Global Climate Change and California: Potential Impacts and Responses (Berkeley: University of California Press).

27. Botkin, D.B., and R.A. Nisbet, 1992, Forest response to climatic change: effects of parameter estimation and choice of weather patterns on the reliability of projections, Climatic Change 20: 87-111.

28. Botkin, D.B., R.A. Nisbet, and L.G. Simpson, 1992, Forests and Global Climate Change, Chapter 19, pp. 274- 290 in S.K. Majumdar, L.S. Kalkstein, B.M. Yarnal, E.W. Miller, and L.M. Rosenfeld, eds., Global Climate Change: Implications, Challenges and Mitigation Measures, (Philadelphia: Pennsylvania Academy of Sciences).

29. Botkin, D.B., L.G. Simpson, and H.J. Schenk, 1992, Estimating Biomass, Science Letters.

30. Botkin, D.B., and R.A. Nisbet, 1992, Projecting the effects of climate change on biological diversity in forests, pp. 277-293 in R. Peters and T. Lovejoy, eds., Consequences of the Greenhouse Effect for Biological Diversity, (New Haven: Yale University Press).

31. Botkin, D.B., L.G. Simpson, and R.A. Nisbet, 1993, Biomass and Carbon Storage of the North American Deciduous Forest, Biogeochemistry 20: 1-17.

32. Simpson, L.G., D.B. Botkin, R.A. Nisbet, 1993, The Potential Aboveground Carbon Storage of North American Forests, Water, Air, and Soil Pollution 70:197-205.

33. Nisbet, R.A., and D.B. Botkin, 1993, Integrating a Forest Growth Model with a Geographic Information System, pp.265-269 in Goodchild, M.S., B.O. Parks, L.T. Steyaert, eds., Environmental Modeling with GIS (New York: Oxford University Press).

34. Hunsaker, C.T., R.A. Nisbet, D.C.L. Lam, J.A. Browder, W.L. Baker, M.G. Turner, D.B. Botkin, 1993, pp.248-264 in Goodchild, M.S., B.O. Parks, L.T. Steyaert, eds. Environmental Modeling with GIS (New York: Oxford University Press).

35. Guggenheim, D., and D.B. Botkin, 1996, CO₂ Offset Opportunities in Siberian Forests, Report to the Electric Power Research Institute, Center for the Study of the Environment, Santa Barbara, CA, EPRI report # TR-106059.

36. Botkin, D.B., 2001, “Energy and the Quality of Life,” Los Angeles Times, Sunday, June 10, 2001.

37. Botkin, D.B., Henrik Saxe, Miguel B. Araújo, Richard Betts, Richard H.W. Bradshaw, Tomas Cedhagen, Peter Chesson, Terry P. Dawson, Julie Etterson, Daniel P. Faith, Simon Ferrier, Antoine Guisan, Anja Skjoldborg Hansen, David W. Hilbert, Craig Loehle, Chris Margules, Mark New, Matthew J. Sobel, and David R.B. Stockwell, 2007, “Forecasting Effects of Global Warming on Biodiversity,” BioScience57(3): 227-236.

38. Bockstoce, J.R., D.B. Botkin, A. Philp, B.W. Collins, and J.C. George, 2007, “The Geographic Distribution of Bowhead Whales in the Bering, Chukchi, and Beaufort Seas: Evidence from Whaleship Records, 1849-1914,”2007 Marine Fisheries Review 67 (3) 1-43.

39. Botkin, D.B., 2007, The Future of Ecology and the Ecology of the Future, pp. 409-414 in Larry L. Rockwood, Ronald E. Stewart, and Thomas Dietz, eds., Foundations of Environmental Sustainability: The Co-Evolution of Science and Policy (New York: Oxford University Press).
40. Botkin, D.B., M.J. Sobel, L.G. Simpson, K. Cummins, and L.M. Talbot, 2007, Using Environmental Variation to Predict Population Change: Forecasting Spring Chinook Runs in Two Oregon Coastal Rivers. Report from The Center for the Study of the Environment available at www.naturestudy.org as a pdf file.

Underlying this belief that our environment has tipping points and we might be nearing one is a deeper belief: that the Earth’s environment is stable, that undisturbed by human influences it would be constant, or close to it.  Allied with this is the belief that our own actions are pushing the Earth toward the edge of a tipping point in ways that have never happened before.

The idea that our environment — nature, as it used to be called — is pretty much unchanging except for what we do is an ancient belief. It goes back to the Greek and Roman philosophers, who expressed it as the great Balance of Nature: that nature undisturbed achieves a permanence of form and structure, and that even when disturbed by us, if we then leave it alone, it will return to its harmonious constancy.

That idea has followed Western civilization down the ages, and in the 20th century was a fundamental belief even among ecologists — scientists who study the relationship between living things and their environment.  But as I’ve shown in my book Discordant Harmonies: A New Ecology for the 21st Century, nature has always changed.  All the climate reconstructions show that change is its only constant property.  To be more technical about this, modern science tells us that natural ecological systems and their environment are non-steady-state systems.  The old idea about nature being constant and able to return to its constant state after disturbance is based on a classical idea of stability — the stability of a machine, like the pendulum of an antique grandfather clock.  Once set in motion, the pendulum goes back and forth, but gradually friction slows it down and it comes to rest exactly where it started.

One of the things that makes it hard to accept the view of environment and ecosystems as out-of-steady-state and part of non-steady-state systems is that we haven’t had ways to think about how such systems change over time.  To make that possible, years ago I and my colleague Matthew Sobel — an applied mathematician, economist, and William E. Umstattd Professor at Operations Research at Case Western Reserve University — wrote a paper called “Stability in Time-Varying Ecosystems.”  (The paper was originally published as Botkin, D.B. and M.J. Sobel, 1975, “Stability in time-varying ecosystems” in  American Naturalist 109: 625 – 646.)

Briefly, we coined and defined two new terms for ecological systems that insist on changing all the time: persistence and recurrence. Instead of expecting an ecosystem, say of tundra near Barrow Alaska, or a population, say of polar bears, to remain constant, we expect instead that their numbers will vary, but within a certain range. This means the bear population will persist within certain limits, an upper and a lower number.  We call this persistence within bounds.  If we take actions that we think might harm the polar bear populations, we can check if there is an effect by comparing its past persistence with current ranges of variation.  (That is, of course, if we have the data to do this.  If we don’t, we’re out of luck as scientists and our management of polar bears lacks an important scientific base, but that’s another story.)

Recurrence is similar.  If an ecosystem or population is recurrent, then the condition it is in now will occur again in the future.  If a population is declining and on its way to extinction, its current population size is nonrecurrent.  Here’s another example.  In 1938 there were only 18 whooping cranes, and there was concern that this species would go extinct, and steps were taken to protect their habitat — their wintering grounds at Aransas National Wildlife Refuge, Texas and their summering grounds at Ramsar Wetlands in northern Canada.  This helped their population to increase greatly, and by 2007 scientists counted 237 at Aransas.  We who admire these cranes hope a population low of 18 never recurs — the population never gets that low again, but that 400 or even more could.

Tipping points don’t work for non-steady-state ecological systems, because they are always changing, kind of sloshing around from one condition to another, and they don’t really have cliffs to fall off of.  Life has persisted on Earth for about 3.5 billion years, during which it has evolved, changed, and adapted to changes many times.  Indeed, many of the changes life has adapted to were brought about by life itself, which has altered the environment locally and globally, adding to that sloshing among system states. Living things and their ecological systems do change a lot.  We can talk about changes that we like and those we don’t like, changes we consider natural or unnatural, but speaking of these as tipping points gets us off the track, away from how these things really work, and interferes with understanding what we could do, want to do, and even should do.

These are the general ideas.  If you want to get into the details, please read Matt Sobel’s and my paper.  Meanwhile, realize that tipping points only happen to steady-state systems, and our environment and ecosystems are not that kind.  There are many helpful ways to consider and discuss the possible effects of global warming.  Tipping points is not one of them.

John McCain has called for building 45 new nuclear power plants by 2030 and 100 eventually. Barack Obama’s Web site says, “It is unlikely that we can meet our aggressive climate goals if we eliminate nuclear power from the table.”
But to what extent can nuclear power really help achieve energy independence?

There’s a problem about nuclear energy that gets little attention. At present, fossil fuels provide 87 percent of the world’s total energy while nuclear power plants provide just 4.8 percent. (All nuclear power plants currently generate electricity, accounting for about 15 percent of world electricity generation, while fossil fuels produce almost 67 percent of the electricity.)

The best estimates put the amount of uranium that can be mined economically (what geologists call the reserves) at about 5.5 million metric tons, and according to the International Atomic Energy Agency, today’s nuclear power plants use 70,000 metric tons a year of uranium. At this rate of use, the uranium that could be mined economically would last about 80 years.

Suppose it were possible to replace all fossil fuels with nuclear power. Suppose that we could use nuclear energy to make liquid and gas fuels to power vehicles, and could do this quickly using conventional nuclear power plants.

We would have to build enough plants to increase energy production by 17.4 times, which means using 1.2 million tons of uranium ore each year. At that rate of use, the reserves of uranium would be used up in less than five years.

Geologists also estimate that there are about 35 million tons of uranium out there regardless of the cost of mining it (geologists call this identified resources). With nuclear power replacing all fossil fuels, even these would be used up in 29 years.

Thus, if the goal is to counter global warming by replacing all fossil fuels with nuclear power, this goal cannot be met.

Advocates of nuclear power point out that it doesn’t have to replace all other sources of energy. Let’s consider that approach.

At a recent meeting, the Group of Eight major industrial countries agreed to reduce carbon emissions 50 percent by 2050. Suppose nuclear energy increased just enough each year to enable fossil-fuel use to decline at a constant annual rate, to 50 percent by 2050, while nuclear power therefore increased to provide 50 percent of the world’s energy.

At this rate of use, uranium reserves would run out by 2019, and the estimated maximum of 35 million metric tons of uranium in identified resources would run out by year 2038, gaining us less than two decades.

There are some important caveats. Exploring for minerals is done on an as-needed basis, and large areas of the world may have been little explored for uranium. Every mining geologist and mine corporation executive will tell you that estimates of total reserves of a mineral are just that – estimates – and that the reserves of many minerals always increase over time.

This approach may be all right for the planning time of mining companies, but it won’t work for a long-term global energy strategy based on adequate supplies of uranium.

Considering the enormous costs of building the large number of nuclear power plants that are contemplated to replace fossil fuels, the United States would be courting disaster if it chose this route with nothing but blind faith that there may be a lot more uranium out there if we only look for it.

We need to know a lot more about available uranium resources and where they are. If they are in unfriendly countries, they might not be available at all.
Nuclear power advocates also argue that it is possible to recover significant amounts of uranium from spent fuel. According to the International Atomic Energy Agency, “In 2004, two-thirds of the uranium used was newly mined; the rest came from civil and military stockpiles, spent fuel reprocessing and re-enrichment of depleted uranium.”

But the amount from spent fuels is not specified, and a reprocessing program to deal with 1.2 million tons of used uranium would be a major undertaking, perhaps not technologically feasible in the near future.

Others suggest that breeder reactors, which produce more nuclear fuel than they use, will solve the problem.

The United States experimented with a few breeder reactors from 1964 to 1994, but they were shut down or work on them halted in the 1990s.
Other nations have tried building them, and some are considering or developing them. But to my knowledge perhaps only one or two breeder reactors are in use and providing electrical energy anywhere in the world, and these are probably not “breeding.”

There are reasons for this: The technology is not there yet, and the reactors are dangerous in themselves, even without considering their potential use in making atomic weapons. They are the kind of nuclear reactors that everybody fears Iran or North Korea might build and use to make atomic bombs.
In sum, the breeder-reactor route, if it is practical at all, is a long way in the future as a major contributor to the world’s energy, and certainly not a way to reduce our dependence on fossil fuels now or in the near future.

The bottom line: From what is known about resources of uranium and the present and future state of nuclear power plants, there is no way that nuclear power can play a dominant role in the world’s energy supply.

This is not to say that it could play no role in a mixed strategy involving many kinds of energy, only that those who continue to press for a greater role for nuclear power must first show that there will be enough uranium to assure that thousands of nuclear power plants built at enormous cost would not soon stand idle – and leave our economy standing idle too.

In 2004 a group of scientists, including myself, met and discussed what needed to be done to improve the ability to forecast the possible effects of global warming on biodiversity.  The result was a paper published in BioScience, the journal of the American Institute of Biological Sciences (AIBS).

In that paper, we proposed a “Quarternary Conundrum” — we found that the fossil record gave results about climate change and biodiversity that did not agree with modern forecasts.  Here is what we wrote about that idea.  (If you are interested in more from this paper, let me know and I will post more of it, or you can obtain it from AIBS.)

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Current forecasting methods suggest that global warming will cause many extinctions, but the fossil record indicates that, in most regions, surprisingly few species went extinct during the Quaternary (from approximately 2.5 million years BCE to the present)—in North America, for example, only one tree species is known to have gone extinct (Bush and Hooghiemstra 2005). Large extinctions were reported mainly for tree species in northern Europe (68% loss of tree genera; Svenning and Skov 2004) and for large mammals (> 44 kg) in the Northern Hemisphere (MacPhee 1999).We refer to this contrast between the implications of modern forecasts and the observed fossil record as the “Quaternary conundrum.” The resolution of this conundrum is key to improving forecasts of climate-change effects on biodiversity. Among the possible explanations are that climate change during the Quaternary was greatly different from climate change forecasted for the future; that genetic and ecological mechanisms, not accounted for in formal forecasting methods, allow the persistence of many species even under rapid climate change; and that factors in addition to climate change could decrease rates of extinction.

Some recent ecological genetics research further deepens the puzzle. For example, the risk of extinction for a species in response to climate change depends on the demography and evolution of genetically differentiated populations across their geographic ranges. If populations are locally adapted, climate change will cause conditions to deteriorate across the species’ range, rather than just at the margins of the range. Modern reciprocal transplant experiments, in which spatial gradients in climate serve as proxies for temporal climate change in the future, show that these fitness losses can be large (Rehfeldt et al. 1999, Etterson 2004). For example, a reciprocal transplant experiment on lodgepole pine in Canada indicated that global warming would slow tree growth and increase mortality, resulting in a 20% loss of productivity (Rehfeldt et al. 1999). Likewise, a study of a prairie annual in the Great Plains of the United States showed a 30% reduction in seed production in climates similar to those predicted for future decades. Ecological genetic data, in each of these cases, predicted different rates of adaptive evolution in different parts of the species’ range (e.g., rear and leading edge; Hampe and Petit 2005) but generally suggested that evolutionary rates would be slower than the anticipated rate of climate change (Etterson and Shaw 2001, Rehfeldt et al. 2002).

Until recently, it was thought that past temperature changes were no more rapid than 1 degree Celsius (^oC) per millennium, but recent information from both Greenland and Antarctica, which goes back approximately 400,000 years,indicates that there have been many intervals of very rapid temperature change, as judged by shifts in oxygen isotope ratios. Some of the most dramatic changes (e.g., 7^oC to 12^oC within approximately 50 years; Macdougall 2006) are actually of greater amplitude than anything projected for the immediate future. Although these changes were probably not equally severe everywhere on the globe, a well-documented rapid warming did occur around the shores of the North Atlantic at the end of the last glaciation, when melting of the ice cover on the ocean suddenly allowed the Gulf Stream to reach the shores of northern Europe. There, temperatures rose rapidly, perhaps as rapidly as anticipated today for the next several decades (Huntley et al. 1997).

What could explain the Quaternary conundrum? One possibility is that migrations were faster than has been thought possible. A large literature examines late-Quaternary range shifts deduced from the pollen record, and recent papers consider models and seed-dispersal mechanisms that may account both for migration across geographic barriers and for rapid invasion of new territory. Sparse populations of several tree species are now known (from genetic and macrofossil evidence, supplemented by detailed analysis of mapped pollen data) to have persisted during the last glacial maximum in regions where very few, if any, pollen grains have been observed—regions that for this reason would be judged well outside the climate envelope for these species (Tomaru et al. 1998, Brubaker et al. 2005, McLachlan et al. 2005, Magri et al. 2006). These populations serve as advance colonists, allowing rapid population growth in newly available habitat.

A second explanation is that low extinction rates during Quaternary climate change may be partially attributable to ongoing adaptive evolution. Theoretical models suggest that adaptive evolution can enhance the persistence of populations in a changing environment even when migration is possible (Bürger and Lynch 1995). And rapid genetic adaptation to climate has already been documented for a few wild organisms for which long-term studies of field populations have been conducted (reviewed in Bradshaw and Holzapfel 2006). Invasive species have also evolved since their arrival in a new habitat in the 20th century, at surprisingly rapid rates of evolution (e.g., Huey et al. 2000).

A long-standing controversy regarding the role of people in Quaternary extinctions of large mammals speaks to the difficulty of quantifying impacts of multiple factors on species loss. The high extinction rate of large mammals has been widely recognized since the 19th century, and extinctions of large mammals and island birds over the past 100,000 years have been the subject of much conjecture. Paul Martin has made the now well-known case that the timing of extinctions followed human dispersal from Afro-Asia to other parts of the globe and that these extinctions resulted from human “blitzkrieg” overkill (Martin and Steadman 1999). But careful analysis of well-documented extinctions in Beringia suggests that human hunting was superimposed on a preexisting trend of diminishing animal population density (Shapiro et al. 2004, Guthrie 2006). These data suggest that the interaction of environmental change and human resource use can have a larger negative impact on biodiversity than either factor alone.

Copyright © American Institute of Biological Sciences, posted with permission.

Dan Botkin