by DK
2006 In Field Notes from a Catastrophe, journalist Elizabeth Kolbert tells the stories of people and places impacted by climate change.
In 1896, Swedish chemist Svante Arrhenius became the first person to argue that carbon dioxide (CO2) emissions caused by human beings could lead to global warming. Arrhenius thought that the average ground temperature could be influenced by carbon dioxide and other “greenhouse gases,” as they are now known, and believed that increasing levels of CO2 would raise Earth’s temperature. More specifically, he estimated that if levels of carbon dioxide increased by 2.5 to 3 times, Arctic regions of the world would see temperature increases of 14–16°F (8–9°C).
Arrhenius was building on the work of scientists Joseph Fourier and John Tyndall earlier in the 19th century. Fourier had wondered why Earth was not a freezing wasteland, when the Sun was too far away to heat it to its current temperature. He knew that heated surfaces—such as the surface of Earth—emit thermal energy, and that the thermal energy radiating back into space should result in colder temperatures on Earth. Something was regulating the temperature, and Fourier theorized that Earth’s atmosphere, made up of various gases, acted like a glass box, containing the air and keeping it warm. Fourier’s hypothesis, although oversimplistic, led to the “greenhouse effect” theory of Earth’s thermal regulation.
John Tyndall was the first to prove Fourier’s greenhouse effect hypothesis. His experiments demonstrated how, when Earth cools down at night—by releasing the heat absorbed from the Sun during the day—atmospheric gases, especially water vapor, absorb the heat (radiation) and cause a greenhouse effect. This keeps Earth’s temperature at an average 59°F (15°C), although in recent decades human activities that release greenhouse gases have pushed this figure higher. For example, the 10 warmest years on record have occurred since 1998.
Water vapor and other gases in Earth’s atmosphere, such as carbon dioxide and methane, trap heat from the Sun and infrared radiation from Earth, raising the planet’s temperature.
“If the planet were a patient, we would have treated her long ago.”
Prince Charles
Fueling a warming world
By 1904, Arrhenius had become concerned about the dramatic increase of CO2 due to human actions—primarily through burning fossil fuels, such as coal and oil. He correctly predicted the influence that CO2 emissions would have on global temperatures, but eventually came to the conclusion that an increase in global temperatures could have a beneficial effect on plant growth and food production.
The burning of fossil fuels has, in fact, increased CO2 levels more quickly than Arrhenius expected, although the planet has warmed less than he predicted. Scientists understand now that global warming is having damaging effects on people and on the environment, and will continue to do so as long as long as emissions continue to increase.
“The atmosphere may act like the glass of a greenhouse … [raising] the mean temperature of Earth’s surface.”
Nils Ekholm
Swedish meteorologist (1848–1923)
The effects of global warming
The Perito Moreno glacier in Patagonia is one of the few glaciers that is still growing. The majority are slowly melting, causing sea levels to rise worldwide.
Since the end of the 19th century, carbon dioxide (CO2) in the atmosphere has increased by about 25 percent, and the average global temperature by around 0.9°F (0.5 °C). Scientific evidence proves that these changes have contributed to melting glaciers and sea ice followed by rising sea levels—around 8 in (20 cm) since 1880—as well as damage to coral reefs. Other phenomena include longer wildfire seasons, more extreme weather, and shifts in the ranges of animals and plants, leading to disease, extinction, and food shortages.
The extent to which global temperatures will increase depends on whether (and how rapidly) global CO2 emissions diminish. Scientists predict that, at the current rate, this increase could range from 0.5°F to 8°F (0.3 °–4.6 °C) by 2100, with the greatest warming likely to occur in the Arctic regions.
See also: Environmental feedback loops • Renewable energy • The Green Movement • Halting climate change
IN CONTEXT
KEY FIGURE
Vladimir Vernadsky (1863–1945)
BEFORE
1785 Scottish geologist James Hutton proposes that in order to understand Earth, all of its interactions should be studied.
1875 Austrian geologist Eduard Suess first uses the term “biosphere” to describe “the place on Earth’s surface where life dwells.”
AFTER
1928 In Methodology of Systematics, Russian zoologist Vladimir Beklemishe warns that humanity’s future is irrevocably linked to the preservation of the biosphere.
1974 British scientist James Lovelock and American biologist Lynn Margulis first publish their Gaia hypothesis—the idea of Earth as a living entity.
Earth has four interacting subsystems: the lithosphere, Earth’s rigid, rocky outer shell; the hydrosphere, which comprises all water on the planet’s surface; the atmosphere, formed by layers of surrounding gases; and the biosphere—anywhere that supports life, from the ocean depths to the highest mountaintops.
The biosphere’s origins are ancient: fossils of tiny single-celled microorganisms that date back 4.28 billion years suggest that it is almost as old as Earth itself. The biosphere extends into every land- and water-based environment, and reaches into extreme habitats, such as the intensely hot mineral-rich waters around hydrothermal vents. It is often divided into “biomes”—common major habitats, such as deserts, grasslands, oceans, tundra, and tropical rain forests.
“Man is becoming a more and more powerful geological force, and the change of his position on the planet coincided with this process.”
Vladimir Vernadsky
Earth the superorganism
Ideas about the biosphere began to emerge in the 18th century, when the Scottish geologist James Hutton described Earth as a superorganism—a single living entity. A century later, Eduard Suess introduced the concept of the biosphere in Das Antlitz der Erde (The Face of the Earth). Suess explained that life is limited to a zone at Earth’s surface and that plants are a good example of the interactions between the biosphere and other zones—they grow in the soil of the lithosphere, but their leaves breathe in the atmosphere.
In The Biosphere (1926), Russian geochemist Vladimir Vernadsky, who had met Suess in 1911, defined the concept in much more detail, outlining his view of life as a major geological force. Vernadsky was one of the first to recognize that atmospheric oxygen, nitrogen, and carbon dioxide result from biological processes, such as the respiration of plants and animals. He argued that living organisms reshape the planet as surely as physical forces, such as waves, wind, and rain. He also introduced the idea of three stages of Earth’s development: first, the birth of the planet with the geosphere, in which only inanimate matter existed; secondly, the emergence of life in the biosphere; and finally the epoch in which human activity changed the planet forever—the noosphere.
Over billions of years layers of cyanobacteria have fossilized to form stromatolites—mounds of sedimentary rock, as seen here at Hamelin Pool, Shark Bay, Western Australia.
Sphere interactions
Scientists believe the biosphere has constantly changed. Oxygen levels in the atmosphere began to rise at least 2.7 billion years ago, as microorganisms called cyanobacteria multiplied. As oxygen increased, more complex life forms evolved that would shape Earth in different ways, eroding and remolding its surface, and changing its chemical composition.
Gradually, elements of the biosphere became part of the lithosphere. Over millennia, dead corals created reefs in shallow tropical oceans. Similarly, the calcite skeletons of trillions of marine organisms fell to the ocean floor, fossilized, and formed limestone.
“I look forward with great optimism. We live in a transition to the noosphere.”
Vladimir Vernadsky
VLADIMIR VERNADSKY
Bo
rn in 1863, Vladimir Vernadsky graduated from St. Petersburg State University aged 22, and did postgraduate work in Italy and Germany, where he studied the optical, elastic, magnetic, thermal, and electrical properties of crystals. After the revolution in Russia in February 1917, Vernadsky became assistant Minister of Education in the provisional government. The following year, he founded the Ukrainian Academy of Science in Kiev. Although his book The Biosphere was not taken seriously by scientists outside Russia for many years, it later became one of the founding documents of Gaia theory.
In the 1930s, Vernadsky advocated the use of nuclear power, and played an advisory role in the development of the Soviet atomic bomb project. He died in 1945.
Key works
1924 Geochemistry
1926 The Biosphere
1943 “The Biosphere and the Noosphere”
1944 “Problems of Biochemistry”
See also: The ecosystem • Biodiversity and ecosystem function • A holistic view of Earth • The Gaia hypothesis
IN CONTEXT
KEY FIGURES
Frederic Clements (1874–1945), Victor Shelford (1877–1968)
BEFORE
1793 Alexander von Humboldt coins the word “association” to sum up the mix of plant types that occurs in a particular habitat.
1866 Ernst Haeckel poses the idea of the biotope, the living space for a range of plants and animals.
AFTER
1966 Leslie Holdridge champions the idea of life zones based on the biological effects of temperature and rainfall variations.
1973 German–Russian botanist Heinrich Walter creates a biome system that considers seasonal variations.
Different parts of the world have varying patterns of plant and animal life, but there are usually similarities over vast areas. These are called biomes, and each one is a large geographical region with its own distinctive plant and animal community and ecosystem. The idea of the biome was first popularized by plant ecologist Frederic Clements and zoologist Victor Shelford in the US, in their key book Bioecology (1939), although its origins date back earlier.
The biome concept took shape as ideas on plant succession and community ecology developed. Clements identified “formations,” large plant communities, which led to his idea of climax communities in 1916. The same year, Clements used the term “biome” to describe biotic communities—all the interacting organisms within a specific habitat.
Like-minded thinkers
Clements was not the only one thinking along these lines. Zoologist Victor Shelford was working toward the same idea. The pair began to meet over the next 20 years, while pursuing their own research, to see how they could combine the worlds of plants and animals. Clements studied plant biomes in Colorado with his wife, the eminent botanist Edith Clements. Meanwhile, Shelford compiled the Naturalist’s Guide to the Americas (1926)—the first major geographical summary of wildlife in the Americas, in which he talked about “biota.” This book laid much of the foundation for later findings.
Ways of looking at interactions in ecological communities took a major step forward when British botanist Arthur Tansley introduced the term “ecosystem” in 1935. When Clements and Shelford published the results of their collaboration in 1939, they were not making a sudden breakthrough—rather it was a consolidation of ideas that had been taking shape over a long time.
The collaboration between botany and zoology was crucial. Only by looking at the totality of the natural world with its dynamic interactions could scientists hope to get a full picture, and Clements defined a biome as “an organic unit comprising all the species of plants and animals at home in a particular habitat.” Even so, biomes have come to be defined principally by vegetation type.
The most important feature of biomes is that they link vegetation and plant communities across the world. There are tropical forests, for example, in every continent, but most tree species appear only in one continent. So, the range of trees within the Amazonian forests is completely different from the range of trees in the forests of Indonesia. Yet both areas are identifiable as tropical forest, because the trees have features in common.
Since Bioecology first appeared, there have been countless attempts to define what a biome is, and many different ways of classifying them. Biomes provide a simple way of understanding global vegetation patterns, but when looked at closely they present a crude way of grouping ecosystems. There is no single accepted classification system, and the only division everyone seems to agree on is that between terrestrial (land-based) and aquatic (water-based) biomes. Many of the same biomes crop up in most systems, such as the polar biome, tundra, rainforest, grasslands, and deserts, but there is no agreed definition and there are marked variations.
The Mongolian steppe belongs to the same grassland biome as the prairies in North America. Despite being on separate continents, they are linked by their climate, animals, and plants.
Threatened coral reef biomes
Coral reefs are such bountiful habitats that they are often seen as the tropical rain forests of the sea. They support a quarter of all marine species and provide livelihoods for half a billion people. Yet they now face catastrophe. Half of all reefs have been lost in the last 30 years, and some experts estimate that 90 percent will be gone over the next 30 years. The main global threats are ocean acidification and global warming. As seas warm, stressed corals expel the algae they rely on for food. They stop growing, lose their color, and often die in what is called a coral bleaching event. Such events are becoming ever more frequent. There are local threats, too, including overfishing, both for the table and for aquariums. Even more seriously, to catch fish for aquariums, sodium cyanide is often squirted into the water to temporarily immobilize the fish, and this kills corals. More brutally, fish for the table are often caught by throwing dynamite into the water. This kills fish, making them easy to scoop up in vast numbers, but it also blasts coral reefs apart.
The climate factor
The one common factor in all biome classifications has been climate, although other “abiotic” factors can also play a part. Climate determines the form of plant growth best suited to a region, and plants that grow in a certain way are restricted to particular climates. The leaves of deciduous trees are broad, with a large surface for light absorption, but little resistance to drying out or frost. Conifer tree needles, on the other hand, are narrow and can survive the harshest frosts. Desert shrubs often have very thin leaves, or no leaves at all, to resist drying out. Biogeographers acknowledge climate’s key role when they talk about “tropical” rainforests and “temperate” grasslands.
Very few species have identical climate requirements. Even among varieties of the same plants, there are variations. The sugar maple of eastern North America, for example, is slightly more tolerant of winter cold than its cousin the silver maple. Although the areas where both trees grow overlap, the sugar maple can be seen far over the Canadian border, whereas the silver maple flourishes as far south as Texas. Since biomes give only an approximate picture of plant and animal distribution, ecologists are constantly devising new systems of classification.
This map shows six biomes across the globe. Each area has distinct flora, as major plant types vary from one climatic region to another. Ocean and freshwater biomes are not displayed here, but are equally important to the biosphere.
Rain, heat, and evolution
One of the most widely recognized systems of classification is the life zones system devised by American botanist Leslie Holdridge in 1947, and updated in 1967. His system is based on the assumption that two key factors, rain and heat, determine vegetation type in each region. He created a graphic depiction of 38 life zones in a pyramid. The three sides of the pyramid represent three axes: rain, temperature, and evapotranspiration (which depends on both rain and temperature). Using these axes, he could plot hexagons showing regions that also reflect humidity, latitude, and altitude.
American plant ecologist Robert Whittaker devised a much simpler gra
ph, with average temperature on one axis and annual rainfall on the other. With these two variables plotted against each other, he was able to divide the graph into nine biomes—from tropical rain forest (the hottest and wettest) through to tundra (the coldest and driest).
Underpinning all these systems is the idea of convergent evolution, which argues that species develop similar traits as they adapt to similar environments. Insects, birds, bats, and pterosaurs all developed wings independently to occupy air space. Different biomes are therefore assumed to develop corresponding life forms in response to similar environmental conditions. However, in recent decades, it has been noted that species can evolve differently in the same biome and also that different stable biomes can develop in an identical climate. While central to understanding life, biomes remain a complex and elusive concept.
Tropical rainforest is the hottest and wettest biome and covers 7 percent of Earth’s surface. One of the oldest biomes, it also contains far more animal and plant species than any other biome.
Ecozones
The short-beaked echidna is one of the most widespread native mammals in the Australasian ecozone. They live in a range of habitats from desert to rain forest.
Biomes are about identifying the similar forms that life takes in response to particular regional conditions such as climate, soil, and topography. However, there are other methods of dividing the world in ecological terms. In 1973, Hungarian biologist Miklos Udvardy came up with the concept of biogeographic realms; this system was then further developed in a scheme by the World Wildlife Fund. The BBC later replaced the term “biogeographic realm” with “ecozone.” Biogeographic realms divide the whole planet according to the evolutionary history of plants and animals. The ways in which continents have split apart and drifted means that species have evolved variously in different parts of the world. Ecozones are therefore based on identifying this diversification. Australasia, for example, is a single ecozone, because marsupials evolved there in isolation from other mammals in the rest of the world.