Science / Medicine : THE GRIM EFFECTS OF GLOBAL WARMING : If predictions of greenhouse effect prove accurate, climate change would wipe out some species of animals and plants and decimate others, scientists say. Manmade obstacles would hinder migration to appropriate habitats.
At the end of the Paleocene period 57 million years ago, nearly half of the species that lived in the deep ocean became extinct. Among them, small, crab-like organisms called ostacods and single-celled species called foraminifera abruptly disappeared from the fossil record for thousands of years, as did traces of worms and other burrowing creatures.
It was the largest oceanic extinction event of the last 90 million years, according to marine paleontologist James P. Kennett of UC Santa Barbara. “The entire community in the deep oceans was zapped,” he said.
Now, new evidence suggests that what happened in the Paleocene may have implications for the current episode of global warming. Research reported last month by Kennett and geologist L.D. Stott of USC indicates that the loss of those species was a direct result of a sharp increase in the Earth’s temperature--the first time global warming has been definitively linked to an extinction event.
Further study of that event, Kennett said, should give insight into the biological effects of the global warming now thought to be occurring as the result of humanity’s increasing release of carbon dioxide and other so-called greenhouse gases into the atmosphere.
That release, which began with the advent of the industrial revolution in the mid-1800s, is expected to increase the Earth’s temperature by perhaps as much as 9 degrees Fahrenheit by the middle of the next century. Among the potential effects of such warming would be: a disruption of agriculture and a shift of prime growing regions northward, perhaps resulting in reduced food production; melting of the polar icecaps, raising the oceans’ level and inundating coastal plains; and sharp changes in weather patterns, bringing droughts to the American Middle West and increased numbers of monsoons to the Indian subcontinent.
But another, hitherto little-considered effect of global warming could be a decimation of the world’s flora and fauna. Fully 15% of species alive today could succumb as a direct result of climate change, speculates Thomas Lovejoy, assistant secretary for external affairs at the Smithsonian Institution.
The warming would force species to migrate northward, so they could remain within their appropriate ranges. At the end of the Paleocene, which was marked by a temperature increase of as much as 25 degrees Fahrenheit, tropical trees and mammals had migrated as far north as Ellsmere Island, off the northwest tip of Greenland.
But during that period, the various species had hundreds, perhaps even thousands of years to carry out their migration and there was apparently no significant loss of either flora or fauna on land.
In the new warming created by humanity, such species will have only a few decades to migrate northward. New studies of the migration rates of plants, especially trees, suggest that is not nearly enough time to prevent decimation as their ranges shift out from under them and new species move in from the south to replace them.
At the end of the Pleistocene epoch, about 10,000 years ago, the Earth warmed by about 10 degrees Fahrenheit over an estimated 1,000 years. Using fossil pollen as a marker, Margaret Davis of the University of Minnesota has measured the speed at which various important tree species migrated in response to that warming. Beech trees managed to march northward at about 15 miles a century, a fairly typical rate that does not bode well for forest survival as the climate shifts an estimated 300 to 600 miles over the next century.
As at the end of the Pleistocene, no extinction of flora, or plants, occurred, presumably because warming also occurred slowly. The only significant extinction of fauna was of large land-dwelling animals, and the majority of anthropologists now believe that they were hunted to extinction by newly aggressive humans.
If no plant extinction and very little animal extinction took place during the warming at the end of the Pleistocene, why should scientists anticipate it now? One obvious reason is that the Earth is expected to warm 10 to 20 times more quickly than it did then.
Another, more subtle reason is that at the end of the Pleistocene, most species had huge ranges, parts of which might have remained climatically suitable even during a massive warming. “With a whole world as a gaming board, they can survive climate change,” says zoologist Paul Colinvaux of Ohio State University. But human activity has shrunk the ranges of many species. “What Davis is showing is that if the trees have to run away from climatic change, then they can’t make it.”
Complicating matters, cities, highways and farms have carved the natural world into small islands, and created barriers for migrating species. “I don’t think (the greenhouse effect) would cause extinctions if the world remained wild,” says Colinvaux. “But most of it is occupied by people.”
In general, scientists expect already-endangered species to be hit the hardest by global warming. “Many species are on the brink,” says Deborah Jenson of UC Berkeley. “In California alone, 600 plants are either on somebody’s endangered list or on a species of concern list; 220 animals are also on one of these lists.”
The barriers of civilization create particular problems for large species of animals and animals high on the food chain. The reason is simple. A herbivore has to eat roughly 10 pounds of vegetation to make a pound of flesh. A carnivore has to eat roughly 10 pounds of herbivore to gain a pound of flesh. The vegetation to support carnivores occupies a lot of space, making them uniquely vulnerable to anything that might shrink their ranges. This is why an earlier warming may have contributed to the decimation of large species in the Americas about 10,000 years ago, and it is also why scientists expect that when shifting ranges start crashing into civilization, big animals will be among the first to go.
Species that depend either directly or indirectly on tidal marshes, such as some birds, fish, and shellfish, are likely to become endangered as rising oceans inundate wetlands.
In general, stressful conditions of temperature or drought reduce reproduction. During the 1988 drought, reproductive success among waterfowl was down by a third, says Robert Peters, a senior fellow at the W. Alton Jones Foundation, which funds efforts toward protection of the global environment.
Among some reptiles, temperature determines sex as the eggs incubate. Warming may result in a preponderance of male alligators, and of females in some species of turtle.
While the bulk of the biosphere will probably suffer from global warming, certain elements may thrive, at the expense of humans. “Tropical diseases and pests will move toward the poles,” says John Topping, president of the Washington-based Climate Institute. “Certain diseases such as malaria will spread across a broader area, barring public health measures that might be taken beforehand.”
Topping says the biggest human health problem from the greenhouse effect will be epidemics among large populations of refugees in developing countries who will flee coastal flooding.
And Colinvaux thinks that people may make the largest contributions to the extinction problem. “If agricultural lands become unarable, politicians will come under pressure to open up parkland to feed the people, and the pressure on the reservation system will be immense. Human societies are going to be disrupted, and when human societies are disrupted, they do damage.”
Scientists believe that the much-talked about global warming phenomenon could have a major effect on plants and animals. One researcher speculates that up to 15% of species alive today could succumb as a direct result of climate change. And, making the scenario more dismal, conditions are much different now than they were during the last warming 10,000 years ago. Here’s a look:
IN THE LAST WARMING: No unusual extinction among plants. In the animal world, only large mammals were hard hit. And mammals might have succumbed to human predation rather than climate change. Most species had huge ranges, parts of which might have remained climatically suitable even during a massive warming. Huge flocks of seed-carrying birds helped move seeds to locations where plants could thrive. IN A FUTURE WARMING: Earth is expected to warm 10 to 20 times faster. Because of human activity, species have far smaller ranges. Cities, highways and farms have created barriers for migrating species. Fewer massive flocks of seed-carrying birds exist. Already-endangered species are likely to be hit hardest; in California alone, one researcher said, up to 600 plants and 200 animals are already being watched. Tropical diseases and pests will thrive, moving toward the poles. A) Carbon dioxide, methane, nitrous oxide and chlorofluorocarbon gases from automobiles, factories, etc., are released into the atmosphere, where they form a barrier that traps heat. Water vapor also traps heat. B) Sunlight is able to pass through the barrier aned warm the Earth, but the resulting heat is unable to escape back into space. C) The resulting greenhouse warming is expected to shift prime agricultural regions northward, melt the polar caps and cause sharp changes in weather patterns.
