Foundations of the Eart: Global Ecological Change and the Book of Job

Rain is a commodity not to be wasted in Uz or in the Bible, in general. In Isaiah 35:6–7, God makes rain in the desert to allow the survival of the returning exiles to Zion. However, in Job 38:25–27, the rain falls in the desert, “where no one lives,” pointedly emphasizing that the distribution of the water solely for the benefit of humanity is not a divine objective in the Book of Job.1 Indeed, a minimization of humanity’s importance in the fabric of nature resonates through the whirlwind speeches,² a point noted in chapter 1. From an anthropocentric view, what is the point of making rain fall on a place humans do not use? The whirlwind question reveals that rain is not just for humans or the ecosystems that immediately support them. It also is for nonhumans and their supporting ecosystems. For example, it rains in the desert for the onager from chapter 4, who laughs at humans and makes its home there. Presumably, it rains for all the other creatures as well. The implication of the whirlwind question is that rain nurtures the planet and its biotic diversity but is not solely for humanity’s needs.³

Deserts are difficult places for many species to survive. For other species, they represent diverse habitats and are filled with remarkably adapted plants and animals. The consideration of how plant and animal species fit into and survive in their environments falls under the general ecological topic of niche theory. The “niche” was formally defined in 1917 by the great California naturalist Joseph Grinnell.⁴ It refers to the set of conditions (climate, soil, other associated species, etc.) that determine where a particular species of plant or animal will be found. Grinnell’s father, Fordyce Grinnell, was an Indian Agency physician to the Oglala Lakota (Sioux) and their chief Red Cloud (Ma

píya Lúta, 1822–1909). Joseph Grinnell was born in 1877 near what is now Fort Sill, Oklahoma, and grew up among the Lakota (Sioux) in what is now the Pine Ridge Indian Reservation in South Dakota. His childhood undoubtedly produced a unique ecological understanding and was likely influential in his formalization of the niche.⁵ The Lakota, like other people surviving on the land, necessarily developed keen insights on what controls where species, particularly useful ones, are located. Grinnell and his niche theory channel these Lakota concepts to ecologists.

There also can be remarkable similarities between totally unrelated species found in the same environments, as the illustration of desert plants in the front of this chapter shows. The phenomenon is called “convergence” and seems evidence for parallel organization among the species that compose ecosystems in similar environments.6 Convergence is often seen as evidence for similar niches to be filled in similar but geographically distant environments. The overall look of ecosystems in similar environments/different places can also be strikingly alike. Job, extremely successful at husbanding a diverse array of grazing animals, would have known about deserts, because the patterns of their vegetation can indicate underground water seeps. After all, he owned “seven thousand sheep, three thousand camels, five hundred yoke of oxen, five hundred donkeys” (Job 1:3). To make good decisions as to what to do with such vast herds, one must anticipate the local microclimate from the landscape condition. Knowing how to “read” a landscape is essential to any grazing pastoralist.

Job would not have been surprised by the somewhat unusual occurrence of “rain on a land where no one lives, on the desert, which is empty of human life, to satisfy the waste and desolate land, and to make the ground put forth grass.” His herdsman’s understanding would have given Job the context to appreciate but not answer God’s question. The kernel of this whirlwind question is not the event of rain in the desert; it is, “Why would God waste water that people so desperately need on deserts?” One answer is, “Perhaps God is not as concerned about people (versus other creatures) as Job would like to think.”

This chapter focuses primarily on the less theological but most ecological part of the “rain-where-no-one-lives” whirlwind question, namely, of how climate (the rain) is interlaced with the vegetation (the desert). As was discussed in chapter 3, matching plants to their environment was on the minds of the early agriculturalists of the Fertile Crescent, who shifted their crops when climate conditions fluctuated.

In taking an ecological emphasis, the present chapter presents some of our historical and current understanding of the couplings between the atmosphere and terrestrial surface. This is a significant piece of the larger puzzle asked by the whirlwind question, “Have you comprehended the expanse of the earth?” (Job 38:18). This comprehension summarizes the ensemble of topics from other whirlwind questions, which connect sea and atmosphere, atmosphere and land-cover change, and the Earth and the Sun. The equally interesting connections among the natural histories of animals and planetary change were covered in an earlier text of mine.⁷

There is one part of this whirlwind question not treated in this chapter, “Who has cut a channel for the torrents of rain, and a way for the thunderbolt, to bring rain?” because it is the topic of other chapters. People have worked hard to try to learn how to make it rain. Rain gods, rain dances, and other rituals, often attended by sacrifices of different intensities, are part of the mythic structure of many different cultures, and so are the calendric celebrations discussed in chapter 5. Many cultures have developed and designed rituals and festivals both to commemorate and induce the coming of the seasons. Chapter 3 points out that land clearing, initially with the assistance of domesticated animals, appears to modify local and regional climate. This topic will be taken up again in chapter 10, which treats the current possibility of directed human alteration of the Earth intended to modify and control the climate—planetary geoengineering.

Throughout the whirlwind speech, Job is asked to explain what he knows about the workings of nature. Probably wisely, Job realizes that he knows nothing comparable to the wisdom of God. The whirlwind questions touch on how different parts of the Earth’s systems function, in the case of vegetation, on their dynamics and on causes of pattern. These are central themes in ecological and environmental science and have been so for quite some time.

At the early edge of history, ancient scholars from non-Jewish traditions were keenly interested in plants, initially for their medicinal properties and later for the factors that control their presence (ancient niche theory). Some of the earliest scientific literature was in the form of botanical herbals, which advised treatment of medical conditions with plants or plant derivatives.8 These were highly pragmatic treatises. For example, the Egyptian Ebers Papyrus, thought to be from 1500 BCE but possibly copied from texts as old as 3400 BCE,⁹ had such cures as, “To kill roundworm [Ascaris lumbricoides]: root of pomegranate 5 ro, water 10 ro, remains during the night in the dew, is strained and taken in 1 day.”¹⁰ A ro was a measure equal to about a tablespoon.¹¹

A transition between these ancient medical herbals and a more ecological view of plants and their environment can be seen in work of Theophrastus (372–287 BCE), a student of Aristotle. In the ninth volume of his book De Causis Plantarum, also known as Enquiry Into Plants, Theophrastus described medical herbs, but he also described their natural habitats and geography.¹² Theophrastus is sometimes called the father of ecology and for no small reason. He experimentally transplanted species to areas outside their natural range to determine if they would grow or flower there. The plant-leaf attributes of deciduousness and evergreenness were observed to vary under different climate conditions, and Theophrastus documented these systematic changes in leaf retention. He also observed that high altitudes and northern latitudes were similar in the pattern of their climate and vegetation.¹³ That climate and vegetation are strongly related remains relevant, particularly in today’s concern over the potential effects of change in climate on the vegetation of the Earth.¹⁴

Mountain vistas provide their viewers with a sense of the unity of nature, particularly the constancy of the relationship between climate and vegetation. Looking at adjacent mountain bases, the slopes are covered in forests of the same mixture of species. Move one’s eyes up the slope, and all of the mountains transition to a different type of forest at the same altitude. This persists for the position of the change from montane forest to alpine heather and for the elevation of the beginning of snowfields at the mountain’s tops. These changes in mountain zones all display a pleasing, ecologically based regularity. Of course, there may be a bit of variation, perhaps thanks to a slope’s different steepness or aspect to the Sun, but the scene speaks to a unity of underlying processes working to form a regular, repeatable vegetation pattern.

Theophrastus understood this unity in mountain vistas and in the parallel changes as vegetation changed with climate and location. Theophrastus’s teacher, Aristotle (384–322 BCE), felt that the world, assumed to be a sphere, consisted of five zones (in Greek, κλίμα or klima; plural klimata). There were two frigid klimata (arctic and antarctic), a torrid klima at the equator, and two temperate klimata between the torrid and frigid. This was a simplification of the even-then-ancient practice of dividing the world into seven such climes.15

Greek geographers placed the inhabited portion of the spherical Earth into various zones according to the angle of the sun’s rays to the celestial axis, the position that today is occupied by the pole star, Polaris, in the constellation Ursa Minor. The word klima, meaning angle or slope, refers to this angle, which corresponds to the latitude of the location. The original seven climes devised by the Greeks geographers ranged from 17°N latitude to 48°N. This system of klimata later was elaborated by Claudius Ptolemy (a Greek-speaking Roman citizen of Alexandria, Egypt, c. 90–c. 168 CE). In Ptolemy’s system, each hemisphere was divided into twenty-four klimata or latitudinal bands.¹⁶ Ptolemy used the length of the longest day as his indicator of latitude. Much of what remains of this Greek geographical knowledge fortunately was preserved through the European medieval times thanks to its translation into Arabic.¹⁷ As the word klimata passed into Latin, eventually to become the English word “climate,” its meaning was broadened to mean a region along with the typical weather associated with it. Thus, in their shared and deep history, climate, mountain slopes, and latitude are conjoined.

By the late eighteenth and early nineteenth centuries, European scientists began a significant synthesis of the relationship between climate and vegetation. In Sweden, Carl von Linné (Linnaeus) developed what was to become the modern basis for naming plants and animals. Linnaeus used a genus/species binomial name for each species in a continuing series of updated and ever more extensive texts starting with plants in 1735.18 A Czech nobleman, Kaspar Maria Graf von Sternberg, established the massive fossil and mineral collection of the Bohemian National Museum (then called the Gesellschaft des vaterländichen Museums in Böhmen), which was initially housed on the ground floor of the Sternberg Palace.¹⁹ Using the relation between climate and plants,²⁰ Count Sternberg reasoned that the difference in past fossil plants in different layers of deposits at a location implied that the past climates of Europe had been very different from the present ones.²¹ Sternberg also championed the use of highly detailed drawings and lithographs to allow museums to communicate their holdings to other museums, for comparative studies. The Swiss botanist Augustin-Pyramus de Candolle and his fellow naturalist Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, produced the first biogeographical vegetation map in 1805, showing the distributions of plants across France, and commented on the environmental factors controlling plant distributions.²² Lamarck is better known for his now-rejected theory on the evolution of species, which involved the acquired traits of the parents being inherited by their offspring. For example, in Lamarck’s concept, the ancestors of giraffes stretched their necks for high leaves and passed the longer necks that they had acquired through generations to produce the current long-necked giraffe. It is sad that Lamarck is now remembered for his failed evolution theory rather than for his groundbreaking work as a natural historian and geographer, but c’est la vie. This latter work added context to that remarkable era of exploration and discovery.

The appreciation of the influence of climate on vegetation intensified after the observations of the biologist-explorers on voyages to the remotest parts of the world.23 The first such voyage of discovery was by the crew of the HMS Dolphin, in 1764–1766. Captain John Byron produced a book, A Voyage Round the World, documenting his discoveries; this started a practice that persisted with later voyages. In the year she returned, the Dolphin sailed again under Captain Samuel Wallis, along with the consort ship, the HMS Swallow, under the command of Philip Carteret, and they made a second circumnavigation in 1766–1768. This second expedition reported on explorations of Tahiti, the Solomon Islands, and Papua New Guinea. Other voyages followed in rapid sequence. The HMS Niger explored Newfoundland and Labrador in 1766. The La Boudeuse and L’Étoile made the first French world circumnavigation in 1766–1768. It also carried the first woman to circumnavigate the world, Jeanne Baré,²⁴ the valet and possible mistress of the ship’s botanist, Philibert Commerson. Commerson also named the day-glo pink- and purple-flowered bougainvillea after the chief of the expedition, Louis-Antoine, Comte de Bougainville.

On August 26, 1768, the HMS Endeavour departed Plymouth, bound for the island of Madeira and then onto its mission to observe the exact time of the astronomical transit of Venus across the Sun, on June 3, 1769, at Tahiti—this was intended to aid a determination of the longitude of Tahiti and was part of the continuing attempt to perfect a methodology for predicting the longitude of a ship at sea. The Endeavour was then to make an exploration of the southern Pacific prior to its return to England. Captained by James Cook, they landed on and claimed the Society Islands, New Zealand, and Australia for Great Britain. They mapped the coast of Australia, ran aground on the Great Barrier Reef, made repairs, and eventually returned to England via Batavia (modern-day Jakarta, Indonesia). The Endeavour carried three naturalists. Joseph Banks, the famous British naturalist, headed the group. Banks had hired Daniel Solander, a Swedish student of Linnaeus at Uppsala University, and Herman Spöring, who was Solander’s assistant naturalist. Alexander Buchan and Sydney Parkinson (landscape and natural science artists), along with four servants, filled out the Banks entourage.25 They stopped in Batavia to make more repairs before their return home. Batavia was a pestilent city plagued by malaria and dysentery. It was the death of many of the sailors on the voyages of discovery.²⁶ Spöring and twenty-nine others from the Endeavour, including the remarkable Polynesian navigator Tupaia (see chapter 6), died from diseases there. Of Banks’s nine-man group, only four people (Banks, Solander, and two of the servants) survived the voyage.²⁷ Banks went on to great fame. He became president of the Royal Society and served in that role for forty-one years. He was a great promoter of international science and scientific exploration as well as of the colonization of Australia. As a mentor and promoter, he championed multiple generations of young natural scientists.

The biological discoveries that Banks and his colleagues brought back on the Endeavour were scientifically astounding. The continent of Australia had been effectively separated from much of the world for many millions of years and fully isolated when it broke away from Antarctica about fifty million years ago. It had flora and fauna that had been independently evolving since this time of separation. If the voyages of discovery are analogues to the modern era of space exploration, the observations from Australia were equivalent to finding life on the Moon or Mars—novel, surprising, speculation generating, unpredictable, and theory challenging. New information, new theories, and new scientific questions boiled up from attempts to understand the source and function of this alternative continental-scale biota.

The voyages of discovery spanned well over a century, starting in 1764 with the voyage of the Dolphin and ending in 1899 with the return of the German steamship Valdiva from her mission of charting the deep water on the front of the Antarctic ice shelf.²⁸ The goals of the explorations transitioned from charting new regions and returning drawings and specimens of their novel flora and fauna to Europe, to the search for the Northwest Passage and surveying polar regions, to the mapping of the world’s coastlines and delving the depths of the seas. The role of the exploratory voyage faded, and in its place a system of national maritime study centers with laboratories and dedicated modern research vessels evolved. Nonetheless, the voyages and their reports and biological findings electrified the imagination of natural scientists of their era and continue to do so today.

Two fundamental biological/ecological questions were sharpened by the voyages of discovery. First was the attempt to understand the remarkable diversity of species that were found on these explorations. There were so many more species than anyone had imagined! How did they come into being? Answering this question eventually led to the theory of evolution formulated by Charles Darwin, himself a member of one of the voyages (the HMS Beagle, which circumnavigated the world from 1831 to 1836).29 The co-originator of evolutionary theory, Alfred Russel Wallace, also was an explorer, initially of the Amazon basin and later of the Indonesian archipelago. Formulation of their theories on evolution propelled studies of the nature of genetics and heritability. This was followed by inquiry on the nature of the gene and to modern molecular biology.

The second fundamental question from the voyages asked what caused the regularity in the biological and ecological systems that were found in different environments all over the world, even when the species in different places were unrelated. One facet of this question involves elucidating the basic causes of climate/vegetation relationships. As has already been discussed, this topic has remarkably deep historical roots. The exploratory biologists of the eighteenth and nineteenth centuries were astounded by the array of strange animals, novel plants, and different human cultures they witnessed. Notably, they developed theories on causes of ecological convergence—similar ecological patterns in the plants and animals in distant regions with similar climates.

Alexander von Humboldt stands out as the most conspicuous example. He was a holistic thinker with a unique capacity to record biological and cultural details coupled with a fascination with a diversity of environmental data.

While growing up on his family’s estate near Berlin, he developed a keen interest in natural history. Carl Ludwig Willdenow, one of the earliest and best-known plant geographers, mentored young Alexander and encouraged his interest in plant geography.30 Humboldt read books from the voyages of discovery, particularly Bougainville’s Le voyage autour du monde, par la frégate La Boudeuse, et la flûte L’Étoile (Journey Around the World…, 1771), which described his circumnavigation, and Georg Adam Forster’s Voyage Round the World (1777), which chronicled his observations while with Captain James Cook’s second voyage to the Pacific.³¹ Humboldt was to later meet Georg Forster while a student at Göttingen University. They became close friends.

Humboldt finished his formal education at the Freiberg Mining Academy in 1792 and took up a position with the Prussian Department of Mines as a mine inspector. His work gave him experience with a wide range of surveying instruments and other scientific devices, which served him well during his later explorations.³² He also appears to have decided upon his course in life. Buried in a footnote of the first paper he produced on primitive plant species found in the Freiburg region, “plant geography traces the connections and relations by which all plants are bound together among themselves, designates in what lands they are found, in what atmospheric conditions they live.”³³ This is the question of understanding the climate-vegetation relationship writ large. The illumination of this opinion was to frame the remainder of his life. His father had died when Alexander was nine years old. With the death of his widowed mother in 1796, he resigned his position as mine inspector to follow a career in science and exploration.

He initially planned an expedition to the West Indies, which did not materialize.34 In 1798, he developed a plan to explore Egypt with the outrageously unconventional fourth earl of Bristol and traveled to Paris to equip himself with scientific instruments.³⁵ This Egyptian exploration also unraveled. However, while in Paris he met Nicolas Baudin, who was in the process of organizing another voyage around the world funded by the French government.³⁶ Humboldt was invited to join the scientific crew of the expedition. One can only imagine Humboldt’s delight to be given the opportunity to sail the world himself. One can equally imagine the disappointment when the expedition was cancelled.

During this emotional rollercoaster of developing and dashed expectations, Humboldt met Aimé Jacques Alexandre Bonpland, who was to have been the botanist on the cancelled Baudin expedition.³⁷ Bonpland and Humboldt joined forces and eventually traveled to Spain. They were granted permission by Carlos IV to explore Spanish America, if they were prepared to pay their own expenses.³⁸ They departed La Coruña, Spain, aboard the ship Pizarro, on June 5, 1799, bound for Cumaná, Venezuela, where they arrived on July 16, 1799.³⁹ The day he sailed he wrote a friend, Karl Freiesleben, “I shall try to find out how the forces of nature interact upon one another and how the geographic environment influences plant and animal life. In other words, I must find out about the unity of nature.”⁴⁰ On the way, Humboldt and Bonpland stopped in the Canary Islands, where they climbed the recently active volcano Pico de Teide and descended into the crater. They were to be away from Europe for over five years. Humboldt and Bonpland returned to Bordeaux on August 1, 1804.

In his exploration, Humboldt had performed daring feats. During a dangerous boat journey—made all the more so because he could not swim—he first demonstrated that the Orinoco River drainage exchanged waters with the Amazon basin, a feature unique among the major rivers of the world. Along with Aimé Bonpland and Carlos Montúfar, he climbed to 5,875 meters on the tallest mountain in Ecuador, Mt. Chimborazo. Blocked by a crevice, they could not reach the 6,268-meter summit. At that time, Chimborazo was thought to be the tallest mountain on Earth. In fact, if one measures the heights of mountains as being the distance from the planet’s center to the mountain’s top (and not the conventional measurement of height above sea level), it is the world’s tallest mountain. However one measures it, theirs was the highest ascent above sea level yet reached by any European mountaineer, a record that would stand for decades.

Alexander von Humboldt also had laid the scientific foundation that would make him the most celebrated intellect of his time. There were crates of scientific material brought back from South America. Humboldt and Bonpland collected sixty thousand plant specimens and discovered around 3,600 new species.41 They settled in Paris and began to organize their vast collections and notes. The expedition would publish thirty volumes of findings.⁴² Humboldt coauthored about one-third of these with Bonpland, who soon left the task of compiling field notes and specimens to take a position in charge of the Empress Josephine’s gardens at Malmaison.⁴³

When Josephine died in 1814, Bonpland married and took a professorship in natural history in Buenos Aires. He would never return to Europe. While on a field expedition near the Argentine border, he was wounded and placed under house arrest in a remote location in Paraguay until 1830. Deserted by his wife, he eventually ended up owning a ranch in Uruguay where he fathered several children with an Indian woman. He died in 1858.⁴⁴

Meanwhile, Humboldt’s old botanical tutor, Carl Ludwig Willdenow, had become the head of the Berlin Botanical Garden in 1801. He came to Paris in 1810 to work with his former student’s material. Willdenow’s Berlin herbarium today contains an inventory of specimens representing twenty thousand species, including a significant amount of the Humboldt/Bonpland South American material. Like Humboldt, he was interested in plant adaptation to the climate, and he noted that plants living in the same climate have common sets of characteristics.

Humboldt became one of the most productive scientists in history.45 His work developed new vegetation/ecosystem-based plant geography and inspired others to follow this creative lead.⁴⁶ According to a recent biographer,⁴⁷ this paradigm shift to a vegetation-oriented plant geography was as significant as Lavoisier’s “new chemistry” from 1789 or Lyell’s “new geology” developed in his book Principles of Geology, from 1830–1833.⁴⁸ The difference is that while Lyell and Lavoisier significantly realigned existing sciences in an enlightened age, Humboldt essentially invented a new science.⁴⁹

Alexander von Humboldt saw his own accomplishments more modestly. When he was in his eighties, he wrote a letter, dated October 31, 1854, to his publisher, Georg von Cotta,⁵⁰ which listed his “only” three accomplishments as:

2. The geography of plants, particularly of the tropical world. This was a grand contribution. As but one example of his influence, his work on the biogeography of plants and his vivid description of tropical ecosystems led Darwin to sail to the tropics on HMS Beagle and was a principal influence on the development of Darwin’s theory of natural selection. In a surviving letter responding to Darwin’s stated appreciation of Humboldt’s work, he wrote, “You told me in your kind letter that, when you were young, the manner in which I studied and depicted nature in the torrid zones contributed toward exciting in you the ardour and desire to travel in distant lands. Considering the importance of your work, Sir, this may be the greatest success that my humble work could bring.”⁵² Darwin carried copies of Humboldt’s work on his own voyage of discovery on the Beagle.

3. The theory of isothermal lines. This accomplishment and previous one are particularly germane to this chapter. Isothermal lines connect locations with the same annual average temperature. As calculated by Humboldt, this temperature is obtained by averaging two daily observations, the temperature at sunrise and at 2 p.m. on each day over the course of a year.53 Isothermal lines change with elevation and latitude. Humboldt noted that they predict the regular variations in the height of snow on mountains (the higher the latitude, the lower in altitude is the line of permanent snow) and vegetation features (tree lines, transitions from evergreen to deciduous forests, etc.).

Humboldt collected copious measurements on the state of the environment both regularly and everywhere he went. From this myriad of observations, he decided that isothermal lines provided a general summary of the global pattern of environment and vegetation over the vast and biologically complex regions he explored. Humboldt probably would not have viewed isotherms as the sole “limiting factor” for vegetation interacting with climate. Humboldt saw the world as full of strong interconnections—“Alles ist Wechselwirkung” (everything is interconnected) was his slogan.⁵⁴ Isotherms were measurements that best captured the entire interconnected physical, chemical, and biological interactions in what might nowadays be called an ecosystem—even though that term was not formalized until well over a century later.⁵⁵ Humboldt inspired a succession of globally oriented plant geographers who worked to perfect world vegetation maps.

The first global-scale vegetation map was developed in 1872 by A. H. R. Grisebach.⁵⁶ This two-volume 1,300-page opus described the vegetation of different zones. The first section of each vegetation description was titled “Klima” and described the climate of the region. This was followed by detailed accounts of the species in different regions. He also designated some fifty-four plant forms to develop appearance-based vegetation categories. Many of these forms have a strongly ecological focus (bamboo, banyan, liana, steppe grass, annual grass, etc.); others are more taxonomic (cactus, palm, ferns, bromeliads, etc.). Despite all of this description, Grisebach’s tome has but one illustration, the first world vegetation map, folded in the back of his book.

A. F. W. Schimper published a text in 1898 that also included a world vegetation map, this time with the biomes still used in modern vegetation: tropical rainforest, needle-leaved forest, savanna, steppe, heath, dry desert, tundra, cold desert, etc. His book, which was produced slightly more than twenty-five years after Grisebach’s, displays hundreds of photographs illustrating the remarkable diversity of the planetary vegetation. Allowing the reader to see the vegetation observed on the voyages of discovery, Schimper’s book combines an armchair explorer’s photographic tour through the marvels of the planet’s diversity with a scientific account of the vegetation.

The Danish ecologist Christen Christensen Raunkiaer developed a categorization of plant forms based on the height of what he called “perennating tissue.”57 Perennating tissue becomes inactive during cold (or dry) periods and, when conditions are favorable, then produces new plant structure. The buds on the ends of branches of trees and shrubs, which produce leaves and twigs in the springtime, are familiar examples of perennating tissue. Trees and shrubs with buds in the ends of their branches were called phanerophytes in Raunkiaer’s classification. Plants surviving in harsh environments protect their perennating tissue in different ways, and these patterns are used to develop a classification of life forms. The proportions of different life forms in a local plant community are related to the environment and respond over time to, for example, experimental manipulation of shelter.⁵⁸ At the global scale, for example in tropical rainforests, phanerophytes with exposed perennating tissue at the end of branches (trees or vines) comprise virtually all of the plants. In moist tundra vegetation, hemicryptophytes, with their perennating tissues protected near the ground surface, predominate. In another similar classification, plants in different climates have unique physiological adaptations allowing them to survive minimum temperatures.⁵⁹

Climate maps reinforced the importance of the interconnection between climate and vegetation.⁶⁰ For example, in the Köppen climate system,⁶¹ climate is initially divided into main climate zones (equatorial, arid, warm temperate, etc.) that also relate strongly to broad categories of vegetation. There is not a lot of difference between these categorizations and the klimata of Aristotle and Ptolemy millennia ago. Subordinate categories in some cases have embedded vegetation formations (desert, tundra, etc.). Different climates are delineated by temperature, precipitation, and the seasonality of precipitation.

Seasonality in rainfall separates areas in which the rain does not occur during the most favorable season for growth from those in which it does. Savannas receive their precipitation in summer and are rain-green. They lose their leaves in the dry season. Mediterranean shrublands have winter rain and are mostly evergreen. Detailed climate maps often show climates for locations that have no weather stations (for example, the tops of mountains in remote locations). These climate maps are often based on observing the vegetation there and inferring an expected climate pattern.

Two hundred years after Alexander von Humboldt, we have learned a lot about the vegetation of the Earth and how it is related to climate, soils, and associated human society—all classic Humboldtian themes. Attempts to understand more clearly environmental interactions with the planet’s vegetation have continued to occupy ecologists to the present day. Ecologists still have a lot to argue about and many theories to test. However, we have a substantial new problem, one with which the plant geographers from earlier eras did not concern themselves.

To paraphrase Alexander von Humboldt, Alles ist Wechselwirkung aber einige Verbindungen neue sind—everything is interconnected, but some connections are new. We are challenged to understand what the future vegetation might be on our planet with a different, human-altered climate and a level of carbon dioxide (along with other greenhouse gases) in the atmosphere not seen for millions of years.

Two interdependent, fundamental issues must be resolved to evaluate the effect of climate change on ecosystems. First, what aspects of the ecosystem does one wish to understand? How is the ecosystem resolved in time, space, or complexity? To understand climate change’s effects on vegetation, must one understand the leaf response, the whole plant response, the population response, or somehow all of these and more? If so, how does one synthesize among these levels to understand the ecosystem’s response to climate change?

The understanding of the appropriate factors to consider, sometimes called the “scale problem,” remains a challenge in formulating models to predict future vegetation patterns. Vegetation responses to future climate change are hard to predict. Because of the complexity of these issues, future predictions are often accomplished by applying computer models. The expectations of and suspicions toward computer models held by the general public—and by scientists as well—range from a belief in the models by some to a complete disbelief of the models by others. As was pointed out in chapter 1, “belief” is a loaded term when used in scientific discourse.

Models do have advantages over consulting experts, conducting shouting matches, or querying oracles to predict the future. The assumptions that are used to formulate ecological models may vary from one model to the next. What assumptions have been used to formulate the current suite of ecological models being used to assess the effects of a global change in climate? It is helpful to group these models into categories based on how and what their creators choose to emphasize in a given model’s formulation.⁶²

Different ecological models conclude that the climate changes associated with human-caused global warming could significantly change the vegetation of this planet. There is plenty we do not know and likely need to know. Models are abstractions, and they assume the important factors to understand at particular scales of time and space. Will there someday be the perfect model to predict how the vegetation will change? Perhaps. Currently, we have a multiplicity of ecological models. Some may be correct on a given scale, others correct at other scales. Hopefully, ecological modelers are taking different paths toward the same truth. When several different models converge upon what is called a “robust conclusion,” an outcome that persists in spite of the differences in model formulation, one is inclined to take such an outcome seriously. What are these different modeling paths, and where do they seem to be taking us in our understanding of how climate change might produce vegetation change?

The first global-scale application of this procedure used what is called Holdridge life-zones to assess greenhouse gas–related climate-change predictions using a database of about eight thousand weather stations.63 In this case the expected vegetation is predicted based on a heat index, much like Humboldt’s isotherms; the annual precipitation; and an estimate of how much water the vegetation could use, if water were in unlimited supply. Results showed a substantial change in global vegetation with greenhouse warming predictions. Subsequently, considering several different predictions of climate change,⁶⁴ between 35 and 45 percent of the Earth’s vegetation was altered at the biome level (grasslands turning into deserts; arctic tundra turning into boreal forests, etc.). Change focused strongly on vegetation in the higher northern latitudes. There was also a substantial shift toward drier vegetation types across much of the Earth. Changes of 35 to 45 percent in the Earth’s vegetation are worrisome numbers. They imply a considerable displacement of agricultural and grazing systems and a potential disruption of the conservation of species using the current suite of nature preserves and parks (discussed in more detail in the following chapter). In 1994, a Holdridge-model vegetation-covered terrestrial surface was included in a general circulation model, the first attempt to include changing vegetation directly in a global climate model.⁶⁵

As one might expect, researchers used other theories of climate and vegetation relations to map climate change using the same procedures. The Russian scientist M. I. Budyko developed a bioclimatic theory on the relationship between climate and vegetation by using the radiation balance and a dryness index.⁶⁶ When this Russian climate/vegetation model was applied to predict climate changes, the effects were also significant.⁶⁷ They implied, among other things, the shifting of the northern boreal forest of Russia virtually out its current boundaries.

One disturbing aspect of these evaluations of the change is the possibility of a so-called runaway greenhouse effect—that a change in vegetation from warming produces increases in the rate of natural releases of greenhouse gases, which then promotes more warming. Over the long term, this appears not to be the case.⁶⁸ However, on the short term (hundreds of years) processes that release greenhouse gases (thawing of permafrost in the higher latitudes, destruction of forest by wildfires, increasing the rate that microbes break down carbon in the soil) outpace the processes that remove the greenhouse gases from the atmosphere (migrating trees onto the tundra, regrowing forests, storing carbon during ecological succession).⁶⁹ Thus, the initial response of a warming planet’s terrestrial ecosystems is to release more greenhouse gases and produce a positive but certainly not desirable feedback.⁷⁰

Elgene Box designed a set of plant forms designed to be related to climate variables.71 He started with the premise that features of a plant that are involved in its water and energy balances are the key consideration, an idea strongly indicated by the sometimes striking convergence in the form of unrelated plants in similar environments. This is shown for a pair of desert plants at this chapter’s start.

A full-blown application of Box’s approach uses nineteen structural types primarily having to do with the size and pattern of branching of the plants (trees, shrubs, grasses, etc.) along with dimensions involving relative plant size, leaf type, leaf size, leaf structure, and leaf photosynthesis habit.72 He kept it simple. For example, life forms vary in their height by being tall (large), normal, short, and dwarf.⁷³ Even so, in Box’s scheme, the 19 structural types × 4 plant sizes × 4 leaf types × 4 leaf sizes × 6 leaf structures × 7 photosynthetic habits equals more than 500,000 theoretical plant life forms. Some of these combinations are illogical, such as leafless trees with large leaves, and can be eliminated, and other combinations either do not occur in nature or are very rare. Virtually all of the world’s plants fall into around one hundred of Box’s life forms. The responses to climate of each life form are determined with respect to several temperature variables, measures of aridity and rainfall, and the seasonal pattern of these variables. One can then apply the computer “painting” method described above to all of the locations for each of the hundred or so life forms. For a given place, the vegetation is the collection of the life forms that can survive there. Box’s life-form classification produces descriptive, sometimes almost poetic, names for the different elements of the vegetation (for example, rain-green broad-leaved trees, xeric tuft-treelets, leaf-succulent evergreen shrubs). Change the base climate data to that expected in a greenhouse warming scenario, and the future vegetation changes significantly.⁷⁴ These changes confirm the patterns seen in the simpler vegetation mapping procedure already described.⁷⁵

The life-form approach does have the advantage that it can predict novel vegetation not seen today with new climates. We know this happened in the past; it may be the case in the future. The overall implication of this alternative approach is for significant change in the Earth’s vegetation given global warming.

One can map plant species according to their climate niches, in the sense of Grinnell. An initial study⁷⁶ mapped the changes in the distribution of four North American trees—eastern hemlock (Tsuga canadensis), American beech (Fagus grandifolia), yellow birch (Betula lutea), and sugar maple (Acer saccharum)—in response to two different climate models simulating climate change associated with a doubling of carbon dioxide in the atmosphere.⁷⁷ Very much in the spirit of Alexander von Humboldt’s isotherms, the species’ ranges were based on average January and July temperatures. The species’ range changes are large, somewhat larger than those seen in the vegetation-type or life-forms methods. While the details are different, the larger patterns are consistent.

A similar European study78 evaluated two important European tree species ranges—beech (Fagus silvatica) and Scots pine (Pinus sylvestris)—responding to climate change predicted for a doubling in CO₂ by two other climate models.⁷⁹ As seen in the North American case, the displacements in the ranges of the species are substantial. The potential future range of the species under such conditions of climate change would not overlap with the current species range over areas the size of large European countries. Several species of European birds also would be displaced—for example, the parrot crossbill (Loxia pytyopsittacus), which is highly dependent on Scots pine cones for food.⁸⁰ One would expect the bird to be completely shifted from its present range. A similar habitat evaluation in Australia of fifty-seven threatened vertebrate species found that a 1°C warming should reduce suitable habitat for 84 percent of these species.⁸¹

Such species-niche-based models have been compiled for large collections of plant and animal species. When species ranges are compiled into maps of expected communities, changes at the community level can be predicted as well. Significantly, these modeling approaches have been tested successfully in predicting vegetation from past climates—an implication that they might be similarly capable in their future predictions.⁸²

An even more detailed approach to evaluating climate change’s effects on the Earth’s vegetation is to predict how climate change might affect the birth, growth, and death of individual plants. Such a model is categorized as an individual-based model (IBM). With the development of increasingly powerful computers, several different scientific disciplines (physics, astronomy, ecology) developed IBMs that task computers to bookkeep changes and interactions of many individuals to produce a prediction of the overall system’s change. For example, astronomers simulate hundreds of thousands of stars and their interactions to understand how galaxies form. Early versions of these models in ecology were developed by population ecologists interested in including animal behavior in population models,⁸³ and these led to a diverse array of applications for fish, insects, and birds.⁸⁴ In forests, models that computed the interaction of each tree with the others around it could predict the changes in the forests as the trees grew over time.

One class of individual-based models, which were developed for forests but have now been applied to grasslands and savannas, are called gap models.85 These models feature relatively simple estimates of how trees function.⁸⁶ They use the considerable body of information on the more common temperate- and boreal-forest tree species (how fast they grow, what is required for seedlings to survive, how tall trees of a given trunk diameter are, how long they live, etc.) to develop the rules to grow trees in a simulated forest. Other simple rules include interactions among individuals (shading, competition for limiting resources, etc.) and equally simple rules for the birth, death, and growth of individuals. The simplicity of the relations in the models has positive and negative consequences. The positive aspects are largely involved in the ease of estimating model parameters for a large number of species, the negative aspects with a desire for more “correct” formulations.⁸⁷

The entry of gap models into climate change prediction sprung from their reconstructions of the vegetation of past climates.⁸⁸ This particular class of models since has found wide application in the prediction of climate change effects.⁸⁹ Two special issues of the journal Climate Change have reviewed the gap-model applications for climate change assessment.⁹⁰ These models project significant changes in species composition, vegetation structure, productivity, and standing biomass in response to climate changes at regional and continental scales.⁹¹ These results are in agreement with the other methods used to paint the Earth with a new vegetation induced by a climate change. They have the advantage both of predicting the rate of vegetation change and the formation of novel plant communities under different climates. Because of their detail, these models require powerful computers (or a lot of computer time) to be applied over large areas.

Different researchers have sought to modify these types of models and speed them up computationally. One simplification represents the species in the models by fewer “functional types” to help with the sometimes difficult problem of estimating the model parameters used for each species, particularly in tropical forests. This approach has been pioneered on tropical rain forests with applications in Borneo, French Guiana, and several other tropical locations.92 Other functional type approaches have been used on the deciduous forests of Tennessee and northern China.⁹³

One of the products of a gap model is the statistical distribution of the sizes of all the trees. The Japanese ecologist Takashi Kohyama produced a sophisticated model predicting change in tree-size distributions over time for tropical rain forests in Borneo.⁹⁴ The Kohyama approach, fused with gap models and plant production models, has found application in predicting forest dynamics in the Amazonian rainforest.⁹⁵ However, without using these methods for reducing the computing demand, maps of climate change’s effects on boreal forests have been produced by direct application of a gap model to simulate forest change at each of thirty thousand gridded locations across Eurasia.⁹⁶ In this study, a positive feedback effect was noted—changes in the mixtures of deciduous to evergreen vegetation under climate warming made the Russian landscapes reflect less of the Sun’s radiation into space and increased the degree of surface warming.⁹⁷

Whether one paints the Earth’s vegetation in response to climate change using relations with climate and vegetation, climate and components of the vegetation, climate and plant species, or climate and individual plants, the overall patterns are similar. The 2°C to 5°C increase in average global temperature predicted by climate models that reflect our understanding of the response to the Earth’s climate is large. Indeed, it is large enough to be highly disruptive to natural and human systems.

But these grim evaluations generally do not consider that, while CO₂ is a greenhouse gas being released in large quantity by human activities, mostly from increasing burning fossil gas, petroleum, and coal, CO₂ is also necessary for the process of plant photosynthesis. Will the so-called CO₂-fertilization effect stimulate plant performance as we introduce more CO₂ into the air? Will our grandchildren inherit a manmade Garden of Eden, with our crops growing at ever increasing rates? One answer might be, “Do you feel lucky?” Another might be to use an entirely different class of models to investigate the scientific state of understanding of this problem.

Another representation of vegetation and its change is to emphasize the ecosystem’s function as one of circulating materials through ecological processes. Models based on this viewpoint and much of their mathematical formulation initially came from procedures used in medicine and pharmacology to follow the movement of drugs and other tracers through the body.98 These approaches were initially applied to ecosystems in the 1950s and 1960s, when concern over the transfer of radioactive isotopes through natural environments to people was sponsored by the U.S. Atomic Energy Commission (USAEC). Background research involved laboratory studies and field work as well as direct measurements of rates of transfer of isotopes injected experimentally into natural environments in whole-ecosystem experiments.⁹⁹

The resultant models have been able to assess radioactive pollution problems both on long and short time scales. The half-life of a radioactive isotope is the time necessary for one-half of an initial amount of a radioisotope to be lost to radioactive decay. For isotopes with relatively short half-lives, these models can be used to identify the principal rapid pathways that would carry radioactive doses to humans in the event of a nuclear release.

For example, in the Chernobyl nuclear reactor incident, milk was immediately taken off of European grocery shelves. Iodine isotopes, mostly ¹³¹I with an eight-day half-life, travels to humans through the rapid air→grass→cow→milk→grocery shelf→people pathway. This is a very fast transfer, and relatively little of the radioactive dose is lost to radioactive decay. The iodine radioactive isotopes concentrate in the human thyroid. Cheese, another dairy product, delivers isotopes to humans through a much slower pathway. It takes time to make cheese. By the time cheese products reach people, much of the radioactive iodine isotopes have been lost to radioactive decay. So in Switzerland after Chernobyl, the milk came off of the shelves, but cheese remained for sale.

For longer-lived isotopes, these models of material transfer can determine where and to what levels particular radioactive isotopes would be most concentrated. One problematic isotope, 90Strontium, tends to behave similarly to the element calcium, and like calcium, ⁹⁰Sr concentrates in bones. ⁹⁰Sr has a relatively long half-life (29.8 years). Once in the bone matrix, beta radiation from the ⁹⁰Sr bombards the bone marrow and can induce bone cancer and leukemia. Thus, the central issue in evaluating its potential hazard is the magnitude of the bone concentration—a problem computed today using material transfer models.

In global applications, recent versions of this class of models calibrate the flows of materials into, inside, and out of different types of vegetation cover (polar desert/alpine tundra, wet/moist tundra, desert, tropical savanna, etc.). These transfers alter with changes in monthly temperature and/or moisture conditions, allowing the models to respond to climatic change. This type of model can evaluate change in the uptake and storage of carbon and the associated carbon-based greenhouse gasses.

The current state of accounting for the CO₂ released into the atmosphere by fossil fuel combustion and concrete manufacture (9.1 Pg of carbon, or 9.1×10¹⁵ g in the year 2010)¹⁰⁰ shows that about a third of the carbon emitted is unaccounted for in the global carbon budget. This carbon is thought to be stored annually in the Earth’s forests.¹⁰¹ The worrisome problem is that, if it is being stored in forests, what mechanisms might cause this beneficent storage to cease or even change its sign from negative to positive and become a source. To understand this critical issue better, models that circulate materials and that have more detailed processes are deployed. These models paint the Earth with a covering of leaves to determine how carbon compounds might transfer in and out of the vegetation, particularly if the amount of CO₂ in the air is changed.

Relatively simple models based on leaf physiology of plants can do a remarkable job of predicting the area of leaves expected over the Earth. One application102 implemented a simple model of the energy and water balance of a plant canopy.¹⁰³ The model adjusted the leaf area so that over the course of the year the soil did not dry too much, and after the year the soil had as much water as when the model started. New leaves were added when all the year’s precipitation was not used and subtracted when the canopy used too much water. This produced an estimate of the maximum sustainable area of leaves at a location. With the same paint-the-Earth approach used for other models, the model simulates the expected area of leaves globally and matches maps and satellite data on the vegetation leaf area.¹⁰⁴

Why bother? If the other models that have already been discussed work to predict vegetation structure and species, why is it so important to add physiological detail merely to simulate the area of leaves? These approaches can assess the CO₂-fertilization issue.

We have been conducting an ad hoc global experiment by injecting large amounts of carbon dioxide into the atmosphere since the Industrial Revolution. The concentration of carbon dioxide in the atmosphere has crept up from the 280 parts per million before 1750 to the 400 parts per million as this chapter is being written in the summer of 2013.¹⁰⁵ Given the increasing human emission of carbon dioxide associated with energy consumption, which is increasing with population and consumption in developing economies, the concentration in the atmosphere should continue rising over the next century. Depending on economic development and energy conservation policies, minimal current projections would predict almost a doubling of historical carbon dioxide by 2100 (an increase to 535 parts per million). The last time the planet saw concentrations nearly this high was about three million years ago, when the Earth was 2° to 3°C warmer and the seas were fifteen to twenty-five meters higher than today.¹⁰⁶ Under less “green” policies, the future could see a three-and-one-half-fold increase to 983 parts per million of carbon dioxide in the atmosphere.¹⁰⁷

Will more CO₂ in the atmosphere promote more plant growth, making crops and other vegetation grow better, delivering a Garden of Eden to humanity? One of the effects of having more CO₂ in the atmosphere that can be demonstrated in laboratories is to increase the water-use efficiency of plants. Water-use efficiency is the ratio of the amount of plant produced for a given amount of water lost from the plant. At higher concentrations of CO₂, more CO₂ diffuses into the plant per amount of water lost, so the plants have greater water-use efficiency. This implies that in a high-CO₂ future, plants might grow in places that are currently too dry. Indeed, the steady encroachment of “woody weeds” into grasslands and pastures worldwide is consistent with increased water-use efficiency, but there are a large number of other potentially contributing causes.

It is well documented that plants change their morphology when CO₂ concentration changes. The numbers of stomata per unit area of their leaves has increased by about 40 percent since the onset of the Industrial Revolution,108 and plants are more efficient at using water today than they were 150 years ago.¹⁰⁹ This implies that in response to more CO₂ in the air over the past century and a half, plants have changed the morphology of their leaves mostly to lose less water, not to grow more.

The inclusion of the so-called direct effects of CO₂ (increased photosynthesis or increased water-use efficiency) calls for models that include leaf-related processes. Measurement of these direct effects of CO₂ is difficult, relatively local, and expensive. Free Air Carbon Dioxide Experiments (FACE) use complex instrumentation and release towers to hold a small patch of vegetation at double-CO₂ levels in the open environment. This avoids the complicating effects of putting tents or chambers over the plants in the field, which confounds interpretation of the measured effects. FACE studies have produced complex results. For young forest stands, the net primary productivity response to increased CO₂ levels (approximately 550 ppm) is an increase of around 23 percent,¹¹⁰ a result consistent with a recent model-based study of the effect of increased CO₂ on global net productivity.¹¹¹ The steps to convert this net primary productivity increase into increased carbon storage (respiration, decomposition, tree mortality, etc.) could be expected to bring this number down considerably.

In one FACE experiment, the initial increased productivity from elevated CO₂, which was initially around 24 percent, declined to 0 percent after four years into the experiment.112 The cause appeared to be related to shortages of nitrogen in the soil. Similar “down regulation” in photosynthesis rates has also been seen in a variety of longer-term laboratory experiments.¹¹³ In summary, the evidence supporting a large positive effect of more CO₂ on vegetation is far from demonstrated.¹¹⁴ Don’t bet the planet on a CO₂-fertilization-based Eden just yet.

The models of vegetation change described above are reminiscent of the story of the four blind men describing an elephant. One touches the trunk and declares an elephant is like a hose; another touches the tail and says an elephant is actually like a rope; the third touches the side to find an elephant is like a wall; the fourth touches a leg and thinks an elephant is like a tree. The models described thus far are a bit like this. Is the Earth covered with vegetation, with life forms, with different kinds of plants, with individual plants, with systems that process materials, or with leaves? Or is it covered with all of these things? One can ask on what do models based on these different views of Earth agree. In general, they agree that the climate changes that we are generating should change the living surface of our planet.

Another approach amalgamates the types of models so far described to try to know better the consequences of dynamic climate change—particularly the interaction between vegetation change and climate change. The resultant Dynamic Global Vegetation Models (DGVMs)¹¹⁵ incorporate the mechanisms based on leaf processes in plant canopies with the biogeographical approaches used to paint vegetation on landscapes to simulate better the effects of climatic change.¹¹⁶ These models have been used to determine the degree that increased plant productivity might slow the anthropogenic increase in CO₂ in the atmosphere.¹¹⁷ Because they can include the effects of increased CO₂ on plant processes along with the effects of climate changes, DGVMs also can assess the likelihood that a warming might induce the positive feedback associated with a runaway greenhouse effect.

Large, complex models with many parameters have the appealing aspect of including the many mechanisms that might come into play in the runaway effect. As a downside, they are hard to test, and their solutions may accumulate errors in estimating their many parameters.118 Joining DGVMs and complex climate models is also a demanding computer problem. The challenges are offset by the potential importance of better predicting the dynamics of climate change.

The most computer-efficient way to couple a complex vegetation model such as a DGVM with a complex climate model is to use what is termed “asynchronous coupling” of the models—a climate model is run for a period of time, then its results are fed into a vegetation model, which is then run based on these new inputs; the vegetation model’s results then are fed into the climate model, and so on. In 1997, an asynchronously coupled GCM and DGVM were found to produce small but positive feedbacks on climate.¹¹⁹

Just a few years later at the prestigious United Kingdom Meteorological Office Hadley Centre, a fully coupled climate model with an internal vegetation model called TRIFFID produced quite alarming results.¹²⁰ Under simulated future warming, the terrestrial biosphere initially stored carbon. After about fifty years of simulation, the terrestrial surface instead became a source for carbon dioxide. The effect was so strong that atmospheric carbon dioxide concentrations were 250 ppm greater by 2100. This increase in carbon dioxide added 1.5°C of extra warming in addition to the 4°C increase seen from the increased CO₂ but without the vegetation coupled to the atmosphere. This effect is a significant positive feedback, a self-reinforcing greenhouse effect, in which warming begets more warming. Recently, eleven different coupled GCMs/DGVMs showed vegetation dynamics from large carbon uptakes ranging from the vegetation reducing the greenhouse effect to large releases with the vegetation amplifying a greenhouse warming, all by the end of the century.¹²¹ The TRIFFID model used in the initial coupled simulation described above produced the largest positive feedback over the twenty-first century.¹²²

The results from other simpler approaches discussed earlier in this chapter produced positive feedback results as well. Regional warming in Siberia could produce vegetation composition change that may cause a positive feedback to generate even more warming.123 Vegetation paint-the-Earth methods that track the carbon expected to be released when vegetation changes with climate change produces an emission of fifty to sixty-five gigatons of carbon into the atmosphere released for each 1°C degree of warming, also a positive feedback.¹²⁴ These numbers are close to those of the early TRIFFID experiment.¹²⁵

If we look to the past to see if other natural climate changes produce similar results, the numbers are also close to model predictions for the yield of CO₂ per 1°C warming. One case is the so-called Little Ice Age between the years of 1450 and 1800. Over this period, the climate and atmospheric CO₂ data, the latter derived from ice bubbles trapped in glacial ice, show lower temperatures and also lower CO₂ levels than have occurred since.¹²⁶ As the Earth warmed from the Little Ice Age, changes in climate were followed by changes in atmospheric CO₂ concentration with a lag of about fifty years. The temperature sensitivity of CO₂ emissions from land and ocean sources was between 20 and 60 ppm of CO₂ released per 1°C of warming (with the assumption of no human-generated CO₂ emissions). These numbers all imply a similar sensitivity with positive feedback between the carbon cycle and climatic change.

However, not all of the DGVMs show this response, and many depict a planet where the increased rate of photosynthesis stores more carbon and reduces the warming. The result is a policy maker’s nightmare, a situation where there are tremendous potential effects but relatively little certainty in the results. A recent review concludes by answering questions about the state of knowledge and certainty of climate change as a consequence of global alteration of the chemistry of the atmosphere by humans.¹²⁷ These questions (in quotes) and commentary are:

4. “Are there other factors that might significantly alter our conclusions in trying to answer the first three questions?” Both model predictions and results from field experiments on vegetation imply that elevated CO₂ increases vegetation net productivity similarly over a range of very different vegetation types.128 This and the increased efficiency of plant use of water under elevated CO₂ could moderate vegetation response, but the uncertainty of these effects remains high. A more worrisome effect is noted in cases in which DGVMs are coupled directly with climate simulation models. In these cases, strong positive feedback is seen in the interactions between vegetation and climate. This warming-generating case needs further exploration both globally and locally.

God brings rain not only to the just and unjust, but on the desert as well as the sown land. The wilderness is—quite literally—not Godforsaken. These lines [speaking of the same verses that head this chapter] bring a very important voice into the conversation about the environment and respond to what is all too commonly viewed as the main line of the Bible’s understanding. The notion that all creation is to serve human interests is rejected.¹³⁰