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"Don't like the weather? Just wait a while." So goes the phrase we use here in Ohio to describe our ever changing weather patterns. The quip usually refers to changes over the period of an hour or two. Now it means more. As each year goes by, we seem to have warmer summers with more record-breaking high temperatures, and the winters have been almost balmy at times, with less snow. Part of the reason, at least right here where I live, is the effect that our growing city has. Asphalt and buildings tend to absorb and hold the heat, whereas green plants would reflect it or utilize the sun's energy to help them grow. The rest of the changes are attributed to global warming.

Over the course of decades or millennia, climatic patterns change naturally. And year to year we can expect the unexpected, hence the phrase that started this section. But there is growing consensus in the scientific community that global warming is real and unusually rapid. Moreover, evidence is accumulating that the cause, or at least a significant part of the cause, is of human origin.27

One of the key pieces of evidence comes from the melting of mountain glaciers and polar ice.28 This is a significant worry for those who live along the coasts, for as the ice melts the ocean levels rise and inundate low-lying coastal regions. The process is slow and hard to detect, so it is barely noticeable in the short run. Thus my parents, who live along a marsh on the coast of Georgia, have not taken me seriously when I tell them to sell their house soon. And coastal species that are already on the wane from the encroachment of human civilization have not yet been noticeably damaged by this additional threat.

In places such as the Arctic, where habitat loss and fragmentation are less severe, global warming is the chief threat to biodiversity.29 Melting ice in the Arctic can be shown to have effects on species all the way through the food web.30 At the base of the web are algae and plankton. With thinner ice, the algae are taking over, with less phytoplankton (tiny photosynthesizing organisms) to feed the zooplankton (protozoans and small crustaceans). The dead zooplankton usually rain down to the seafloor, feeding invertebrates at the bottom. Some of those are disappearing, including the clams, which in turn are food for the walruses. Fish also suffer, particularly the cod, who feed the seals. Fewer seals mean less food for the polar bears, as well as for those humans who also hunt seals.

As if the seals did not have it bad enough, if the ice breaks up early in the year due to global warming, then the pups of ringed seals get forced into the water before they are weaned and cannot fend for themselves. Early melting of the ice also affects the Peary caribou, who are already under pressure from Inuit peoples who hunt them. The caribou need solid ice to get from island to island, but now they are falling through the unstable ice. The same goes for bears who hunt seals on the ice; now they have to head for land before they have fed on enough seals to gain sufficient fat for the year.

The consequences of global warming also include increased droughts in some regions, such as those suffered in South Africa during El Niño, and floods in other places. That can be devastating to agriculture, but hey, we're humans, and we can adapt and redistribute our resources. Other species cannot. A significant flood in a small, fragmented habitat could wipe out the remaining populations of rare plant or animal species. Already, as their environments change, the species' isolation means that they cannot migrate to places where conditions are more appropriate for them (as they regularly did during climatic fluctuations of the past31). And drought can affect many marginal species such as the gelada baboon, one of the few open-land monkeys on the threatened list.32

Some life-forms will do well on a warmer earth, but their extra good fortune won't make you happy. Many infectious diseases will thrive under warmer conditions.33 Most notable is malaria, which is expected to spread into more northern latitudes of Europe and North America.34 Is this Malthus's predicted pestilence striking again? To a certain extent yes, but the rise of disease probably will not be enough to seriously stem our persistent population growth — it will just be enough to make us miserable. On the other hand, endangered species — such as the orangutans or gorillas noted earlier in this chapter — may be dealt a deathblow from disease. We just don't know.

Other life-forms, large and small, may also thrive with warmer conditions. After all, the decline of mammalian biodiversity we noted over the past two million years may in part be due to climatic cooling. When the tropics were more dominant on the earth, such as when the early caves of Maka-pansgat were filling up, life was richer and more diverse. There was more energy, the currency of ecology, to go around, and life abounded. Thus I often quip to my students that I am the only one I know who is for global warming. Just think of how biodiversity could thrive, as it did so long ago. The richly diverse flora and fauna of the tropics could spread farther from the equator. Temperate plants and animals could expand into the northern latitudes of Europe and North America. Even in the Arctic, as some species struggle, others could inhabit the land and increase the diversity; already it appears that the harp seal is on the increase.35

There is a catch, however. The threat to biodiversity is not so much that the planet is warming up, but the fastrate at which the changes are taking place. The current rapidity of global warming does not give many species time to adapt to the environmental changes it brings, making them more likely to go extinct. Sound familiar? The same argument was used by proponents of the hypothesis that quick warming after the last glacial phase led to the demise of North America's megafauna. Others argued that human hunting activities, augmented by the exponential growth of their population, were the cause of the massive extinctions. Or maybe one cause exacerbated the other.

Regardless of the academic debates about what happened ten thousand years ago, we can see both causes devastating biodiversity now: other living creatures are getting hit by the double whammy of rapid climatic change and human population growth. Especially fragmented populations cannot keep pace with the changing climate.36 We can see it happening in real time. South Africa, already the country with the second-highest number of extinct plants due to human enterprises, faces even more extinctions with rising temperatures. By 2050, it is expected that summer temperatures in the interior of the country will rise by a few degrees Celsius, with lesser temperature effects—and less rainfall — along the Cape coast. Such changes will be devastating not only to the rare fynbos species of the Cape Floristic region, but also to savanna and woodland plant species.37

Will continued population growth accelerate global warming? The hypothesized causes of global warming are mainly our emissions of greenhouse gases, such as carbon dioxide, which trap solar heat in our atmosphere. Theoretically we could change our behavior, especially here in the United States, where our wasteful employment of energy makes us the world's worst culprit in greenhouse gas emissions. There are also attempts to find ways to remove carbon dioxide we add to the atmosphere, by capitalizing on the ways nature captures it in trees and other growing plants. The idea, basically, is to plant more trees if we burn more coal and oil. But we don't know if that can be accomplished. One thing is certain, all else being equal: more people require more energy, and it would be difficult to stem the tide of global warming by increasing the carbon capture of forests and prairies.

Even if we succeeded in altering our energy use to reduce our emissions ofgreenhouse gases, we'd have to change our agricultural priorities as well, particularly our taste for meat. The digestion process of ruminants such as cattle and sheep involves a process known as "enteric fermentation." One of the byproducts, coming out both ends of the animals in gaseous form, is methane — a greenhouse gas. Now you may not have considered cow flatulence to be a serious threat to the atmosphere, but countries such as Australia and Ireland have had to consider cutbacks on their livestock, their primary source of methane emissions.

On the other hand there may be an up side to the increase of one key greenhouse gas. Plants need carbon dioxide and can grow faster with enhanced levels of the gas, and that may boost crop yields. But the issues are complex. Experiments that raised carbon dioxide levels in pine forests have led to faster tree growth and greater production of cones and seeds, but the trees were smaller than usual when they reached maturity.38 Moreover, some plants may do better than others in such an atmosphere. So, for example, if the pines responded well in a boreal forest, reproducing faster because of their increased seed production and fast growth, it could be at the expense of the birch and aspen trees (which would also then affect the species such as beaver that rely on such trees). So the up side may be down after all.

Thus the causes and consequences of global warming are complex. The ever rising tides along our coastal lands are but one of the problems, for both our economic well-being and ecology, that have alerted otherwise complacent people to the growing concern. But with melting ice caps, at least we'll have more water. Or will we?

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