spread of infectious diseases, which will move farther northward and to higher elevations. The World Health Organization projects tens of millions more cases of malaria and other infectious diseases than exist now. While insects are proliferating, carrying these diseases, three-fourths of all bird species are on the decline. We are thus losing our first line of defense against the threat of disease-carrying insects, since insectivorous birds are the major insect predators. In addition, 26 percent of bat species are threatened with extinction. It is estimated that bat colonies in Texas alone eat 250 tons of insects each night. The loss of many species of birds and bats, while insects proliferate, could lead to an escalation of the use of pesticides, threatening yet more damage to the world's animal species, including us.
The misery of living in a tropical climate as well as the ever-present threat of contracting malaria are the two aspects of climate change through heating that don't get much press. Yet as the tropics begin to spread north and south from the low latitudes of Earth, scourges of the tropics will be coming too. We are returning to a planet with worldwide malaria foremost, but there're more: Ebola, elephantiasis, schistosomiasis, leprosy, rampant intestinal parasites, poisonous spiders and centipedes, new and vicious kinds of ants—all will follow the heat once the barriers of coolness are overcome.
WHILE THE PROBLEMS FOR HUMANS LISTED ABOVE ARE SERIOUS ENOUGH, they are not the two most lethal dangers. The greatest threats posed by global warming are surely famine and war, two Horsemen of the Apocalypse going hand in hand.
Our world sits on a knife edge of global starvation already. We six billion humans, heading toward a far higher number at about the time that rising carbon dioxide levels should begin to stabilize a new pattern of climate, are able to be fed, all of us right now, through the miracle of that long-ago breakthrough of the human mind, agriculture. We need every bushel of grain, however. There cannot be even a single season without harvest in either hemisphere, and this is why there is extreme danger of rapid weather change if there is a Krakatoa-type volcanic explosion or impact of a 100-meter or larger asteroid. Both would put so much dust in the air that one hemisphere or the other (or perhaps both) would have a yearlong or longer winter and thus no crops.
Short-term climate change would be nearly as devastating, and in the long run, more devastating. Neurobiologist Bill Calvin, who has written extensively on the dangers and effects of sudden climate change, suggests that a 10- to 20-year event is far more difficult to deal with societally than is a sudden catastrophe.
Why would a warmed world be in danger of plummeting crop yields? It would seem that plants might flourish in the higher carbon dioxide levels, and with longer growing seasons, perhaps an additional crop could be counted in many areas. This will surely be true for some kinds of human food. Tropical fruits and starches will be available in abundance. But the staple of human sustenance, grains and cereals, the very first crops, in fact, from 10,000 years ago, would suffer. The grain belts rely on cool but not frigid winters, and summers with abundant moisture. Current projections are that the great breadbaskets of Earth, especially the greatest of them all, the American Midwest, would have climate changes that would reduce summer moisture. As droughts become more frequent, yields of wheat, corn, barley, and oat crops would decline.
In the new climate, new regions would become arable that currently are not. Two thousand years ago, northern Africa was the granary for the Roman Empire, but climate change since then caused an expansion of the Sahara Desert and dryness in the formerly fecund states of Morocco, Tunisia, Algeria, and Libya. Those regions would likely get more rain and could perhaps again begin producing bountiful harvests. But it is not likely that they could immediately take advantage of the more propitious climate. Efficient farming is highly mechanized and highly oil intensive. All of the African states listed above are Muslim countries with some of the highest population growth rates on the planet. They do not have a tradition of American-style megafarms, the institutions that create the current food surplus that are so important to help feed so much of the world. They do not have factories that can manufacture the complicated farm machinery necessary. The same goes for areas in Eastern Europe, and all of sub-Saharan Africa. South America could pick up some of the slack, but not all, should the American Midwest become a dust bowl of greater extent than during the Great Depression of the 1930s.
The second great problem is warfare. Nations are unlikely to sit around and watch their populations starve or their national treasuries deplete in order to buy enough food. It will become more and more tempting to simply take or blackmail other countries with nuclear weapons. The desert kingdoms and dictatorships of the Middle East, watching their deserts become even more arid, will become increasingly dangerous as many become armed with nuclear weapons.
The next two centuries will be an interesting time. Our ingenuity as a species could let us get through this. Our darker natures and impulses, however, in the face of sudden climate change, could result in the loss of half of all humans on Earth in a century or less.
AT WHAT LEVEL WILL GREENHOUSE GAS LEVELS PLATEAU AND THEN DEscend, and, more important, how much will the world warm? Our homework, then, is to ensure that the world warms no more than 2 degrees Celsius from its present state. Why is that goal important, and how realistic is it? A guest column by Malte Meinshausen, Reto Knutti, and Dave Frame in the best source for climate change—realclimate. org—on January 31, 2006, is a good discussion and summary of this problem (and offers a possible solution), and if I pirate the spirit of their article, it is (hopefully) for a good cause.
The three authors go through the math, showing that a stable carbon dioxide level of 400 parts per million (to reiterate, we are at about 380 parts per million and rising as I write this in 2006) will yield an 80 percent chance that Earth will warm no more than 2 degrees Celsius. For instance, the rise from carbon dioxide levels of 280 parts per million at the start of the Industrial Revolution to the present level of 380 parts per million has brought about a global temperature increase of 0.8 degrees Celsius, thus calibrating the climate models used to predict future temperature increases that are tied to greenhouse gas concentration increases. The good news is that one of the most troublesome of greenhouse gases now being produced by human activity, methane, has a short life in the atmosphere before it breaks down. Also, the oceans are an effective sink for atmospheric carbon. If human emissions can be sharply curtailed in the twenty-first century, concentrations of all greenhouse gases could begin to decline near the end of the century according to the best models now available. How ever, these are just that—models. This model even lets greenhouse gas levels peak to 475 parts per million for a short time, but we do not go past the 2-degree increase if we can then bring them back down to 400 parts per million before the end of the century.
So how does society do this? Drive less. Drive less-polluting cars. Buy hybrids or electric cars. And there is more. For instance, the authors state:
We need to start taking large amounts of carbon out of the air. One very good way to get this going with positive environmental effects if managed properly is to grow biomass then char it and use the elemental carbon to mix in large quantities deep into soil as "terra preta" or Amazonian dark earths. This has major soil conditioning properties (i.e., reducing conventional fertilizer need by 50 percent).
In other words, use the enhancing carbon dioxide levels to grow lots of new plant material, turn that biomass into charcoal, and bury it into tropical soils.
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