Global Warming: Life as We’ll Know It

News Abroad

Mr. Chew is a Ph.D. candidate at Arizona State University in the School of Life Sciences.

“Global warming,” which may regionally include cooling, drying, humidification, or changes in the seasonality of winds and precipitation, is only one dynamic factor among many contributing to the constant flux of the biosphere. Another factor that will inevitably interact with any climate trend is the continuing redistribution of biota.

Organisms besides humans are affected by climate change, regardless of its causes. If average temperatures rise in the Arctic Ocean and the pack ice shrinks, polar bears and some seals lose habitat. If pack ice becomes rare enough, these animals will be at an ecological, and therefore evolutionary, disadvantage. They might even “blink out” altogether.

Whenever climates shift, there are ecological “winners and losers.” In extreme circumstances, everyone loses. A large-scale glaciation simply scrapes a continental surface clean of not only almost all life, but also accumulated soil. When the ice retreats, life returns and soil building begins again, as organisms begin penetrating from the margins. Likewise, changing sea levels repeatedly inundate and expose low-lying areas of islands and continents, swapping terrestrial for aquatic ecosystems.

As long as there is a supply of potential biotic colonists and a transport mechanism, be it active locomotion or passive drift with winds and currents, some individual organisms, their larvae, eggs, seeds or spores, will eventually arrive just about anywhere. A few survive to “found” new populations. This kind of colonization has always been a fundamental fact of life on earth. It is possible, even likely, that life on earth began only once, and therefore in one place. After that, well, it got around. Being both inclined and equipped to acquire, carry, and exchange, humans have recently become involved in this process as well.

Humans desire and facilitate changes in the environment that seem likely to be advantageous. But purely fortuitous change is uncomfortable, even alarming. Surprised by the arrival of new species in familiar landscapes, we speak of “invasions” or “infestations.” But invasion is in the eye of the beholder. Few people are inclined to describe the occupation of vast areas of North America by maize, wheat, soybeans and other field crops as “infestation,” even though it occurred at the expense of the prairies and woodlands formerly in residence. And hardly anyone worries about transoceanic invasions by tigers, even though there are apparently now more tigers in the United States than in all of Asia. What about zebra mussels in the Great Lakes? That was nobody’s plan. It’s an invasion.

Although it seems blatantly naive today, in the mid-18th century, Karl Linnaeus thought he could turn Sweden into a self-sufficient kingdom. He thought he could achieve this end not by milking wealth from colonies; that opportunity had passed, and Sweden, which couldn’t even establish a Baltic hegemony, never acquired substantial overseas holdings. Instead, Linnaeus wanted to identify important crops and commercially valuable plants and animals in many parts of the world, collect them, and grow them in Scandinavia. He planned a sort of reverse colonization by invading his homeland with exotics. Among other things, Linnaeus hoped to raise mulberry trees, and upon them, silkworms (reputedly carried to southern Europe from China during Justinian’s reign). But his government-backed effort collapsed. The maladapted mulberries, like many other plants, did not cooperate. They languished in the dark and cold of the near-arctic climate.

Decades later, investigators following Alexander von Humboldt attempted to correlate vegetation with latitude, altitude, precipitation and soils. As 19th century explorers mapped the world in ever greater detail, botanists like Augustin and his son, Alphonse DeCandolle, in Switzerland and H.C. Watson in England mapped the ranges of European plant species, and speculated about the correspondence of plants, animals and places. After 150 years of such efforts, Alfred Russell Wallace claimed he could divide the globe into six great regions, or realms, of animal life, and many other writers were proposing ever more detailed divisions and subdivisions. Biogeography was a growing concern.

Early debaters concentrated on problems like “centers of creation,” attempting to reconcile empiricism with the Genesis account. As information poured in regarding not only contemporary geography, but also ancient peoples and fossilized prehistory, a new big picture was developing. Unfruitful Biblical debates gave way to accounts tracing human dispersal, the development of civilizations, and, along with them, the domestication and diffusion of agricultural plants and animals. Within limits, species were obviously moving around.

While establishing a biogeographical baseline of sorts, most of these investigators also realized that new populations of some species were appearing, unbidden, along trade routes, around port cities and even in railroad yards. Strangers sprouted among the detritus of industries like textile manufacturing, which imported raw materials from far-flung producers. Downstream of fleece processing factories, exotic “wool gardens” blossomed.

Upon finding vast stands of European “cardoon” thistles growing in Patagonia, Charles Darwin concluded that the plants must be somehow “specially favoured” there. And every hypothesis concerning biodiversity that followed remains a version of Darwin’s assessment. All else being equal, or at least nearly so, the absence of some previously limiting factor, such as a predator, a competitor, or a disease, allows some species to become established and flourish to an extent not seen in their “native” habitats. Or, alternatively, the immigrant has capabilities that present new challenges to the locals: the immigrant becomes the overweening predator, competitor, or disease where none was known before.

Finally, something was new under the sun. Organisms were entrained in the currents of human commerce. Carried across once-impassable barriers like mountain ranges, deserts and oceans, they were deposited, to live or die wherever they found themselves. Most, like Linnaeus’s mulberries, were doomed by some maladaptation to a brief struggle, without issue; others, however, seemed destined to succeed. Some even became human “camp-followers,” or in the words of Alfred Crosby, our “portmanteau biota,” appearing in practically every human settlement. Thus Hans Zinsser could write of Rats, Lice and History.

All this smacks of an economics lesson. And like many economics lessons today, it involves overseas outsourcing. The very commercial and transportation infrastructure that brings goods and materials in vast quantities from low-cost producers on one continent to consumers on another is also bearing disease organisms, fungi, seeds, eggs and spores, spiders and insects, rats and other small mammals, and sometimes reptiles and amphibians.

As exemplified by the polar bears, climate change puts the existing biota of any set “place” on the map at mounting risk of being selected against. As prevailing conditions change, adaptations that once promoted survival become irrelevant or even disadvantageous. As far as polar bears are concerned, once the ice melts, “there is no ‘there,’ there.” When abiotic factors shift, biotic ones must shift as well. When it happens too quickly for evolutionary adjustments to occur within populations, other populations—outside populations—better equipped to meet the new challenges may take advantage of the opportunity.

Climate change makes “patches” of habitat appear, disappear, or in “time lapse” seem to flow, amoeba-like, across the landscape. With warming climates, alpine and polar habitats shrink, and lowland or tropical ones expand. With cooling, the reverse occurs. Intermediate vegetation, like evergreen forests, moves “up and down” and in between, along various resource gradients. Plants and animals must move along with survivable conditions or die off.

The same applies to aquatic habitats, although the effects are stranger to contemplate. Melting ice caps overlay dense seawater with cold freshwater. As water temperatures change, so too do convection-induced currents. This alters the upwelling of nutrient laden deep waters. The Gulf Stream might change or even fail, with major consequences for Northern Europe. Increasingly exposed to “greenhouse” gases, seawater’s chemistry changes in other ways, too. As more atmospheric CO2 dissolves, waters become more acidic. This makes it harder for corals and mollusks to deposit the calcium carbonate of shells and reefs. Changes thus cascade through entire ecosystems.

Rooted plants cannot move, so their offspring, as seeds, spores, or parts capable of rooting, have somehow to find their ways to more hospitable habitats. Such dispersal of plants has long been an absorbing topic for natural historians. Henry Ridley summarized it at length, and in detail, in 1930. A huge system of terms was coined to describe variations on the theme. The general suffix used is from the Greek, “–chory,” “to spread.” Therefore, anemochory is wind dispersal (a dandelion seed comes to mind) while zoochory is dispersal by an animal—inside or outside it. Human transport is anthropochory, and whether that is considered subsidiary to zoochory will depend on whom you ask.

Johnny Appleseed notwithstanding, anthropochory is also the only form of dispersal that seems readily susceptible to moral censure. Customs officers and state-line vehicle inspectors are in charge of upholding society’s judgments on this issue. Transporters of agricultural weeds and plant diseases are frowned upon. Upon detection, inadvertent carriers are lectured; smugglers are cited or jailed. At the same time, however, there remains a huge transoceanic and transcontinental trade, not only in fruits, nuts, and other produce, but also in nursery stock, cuttings and seeds.

Since (and even before) Linnaeus, opportunists have looked for ways to move plants from continent to continent and island to island, in order to become producers rather than consumers. On his second voyage, Christopher Columbus carried with him numerous old-world fruit trees, domestic animals and vegetable seeds for provisioning his would-be colonists. Captain Bligh was transporting breadfruit trees on H.M.S. Bounty. Rubber production was a Brazilian monopoly until rubber tree seeds were “smuggled” to Kew Gardens and thence to Malaysia and Ceylon.

Almost every commercially grown crop has been substantially relocated in such fashion. In 1898 the U.S. Department of Agriculture even opened an Office of Foreign Seed and Plant Introduction whose function was not to inspect, but to seek and collect plants for production by American farmers and horticulturists. Its most zealous employee, supervisor, and collector was David Fairchild, son-in-law to Alexander Graham Bell. Fairchild proudly claimed general responsibility for bringing 200,000 varieties of plants to the United States.

British colonists in Australia and New Zealand were long dedicated to importing crops and game animals and “amenity species” like songbirds and garden flowers from “back home.” Citizens of post-colonial Australia and New Zealand, belatedly developing a nationalistic sense of nature, are now dedicated to wiping out precisely those same species their ancestors had previously striven to establish. However, these countries are scarcely the same as they were before the introduction of species from back home, and in the words of Australian Tim Low, there are no “final answers, only unfolding stories.”

So anthropochory can be intentional or accidental, celebrated or deplored. Occasionally, we firmly deplore a previously applauded case, like carp, house sparrows, kudzu, multiflora rose, buffelgrass, or even English ivy. But we are just learning to wonder about such cases in terms of climate change. Is global warming “specially favoring” any of the thousands of biotic immigrants? Can we exploit these effects? Can we anticipate them? Should we?

Glib schemes to farm ever higher latitudes tell only part of the story. If anthropogenic climate change accelerates habitat shifting to a pace that other “chories” cannot match, we might even find ourselves moving “wild’ plants and animals to new locations, getting them established, and tending them. Going beyond “restoration” and growing wilderness to order could become another branch of agriculture.

It is already passé to speak of a “state” of the world. Like it or not, all is flux. For the foreseeable future, rapid biogeographical change, linked to climatic dynamics and facilitated by commerce may well be the norm. If reining in the climate proves too difficult, at least redistributing biota will be a familiar exercise. Not easy, but familiar. In a changing world, even that kind of familiarity has a certain appeal.

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T W - 10/21/2006

Having just relocated, taking global warming/climate and future water supplies into consideration when choosing the location, I can heartly relate to many of the points in your article.