Beyond the Planets Limits
Climate Change: Why, How, and What Next?
Climate change is the most serious environmental threat that the world has ever faced. The dangers can hardly be exaggerated. Climate scientists predict that by the end of this century, temperatures could rise 10°F worldwide. But even if they rise by just 5°F, major parts of the earths surface could become uninhabitable and many species on the planet could be wiped out. Just within the next fifty years, there will be more heat waves, higher summer temperatures, fewer cold winters, and rising sea levels. As a consequence, hundreds of millions of people will be at serious risk from flooding, there will be a huge loss of life from excessively hot weather, diseases from warmer regions will become established, some species and habitats will be lost forever, and patterns of agriculture and business will have to change radically. And then, before too long, the whole world may face the even greater dangers of long-term and irreversible catastrophic changes as warming threatens the Greenland ice shelf, the Gulf Stream, and the West Antarctic ice sheet.
Why Is the Climate Changing?
The climate is changing because the natural mechanism known as the greenhouse effect which warms the earthis being increased by human-induced emissions of carbon dioxide and other gases. As the concentrations of the emissions rise well above their natural levels, additional warming is taking place, as shown in the diagram below.
To explain this effect in somewhat more detail, the temperature of the earth is determined by the balance between incoming energy from sunlight and energy constantly being lost from the earth into space. The energy from the sun can pass through the atmosphere almost unchanged and warm the planet. But the heat emanating from the earths surface is partly absorbed by certain gases in the atmosphere and some of this is returned to earth. This infrared radiation further warms the planets surface and the lower strata of the atmosphere. Without this natural greenhouse effect, the planet would be over 35°F cooler than it is nowtoo cold for us to inhabit. However, the greenhouse gases we add to the atmosphere mean that more heat is being trapped. This is leading to global warming and other changes to the climate.
The primary cause of these climate changes is our use of coal, oil, and natural gas. Burning these carbon-based fossil fuels results in the production of carbon dioxide. Globally, these emissions contribute more than two-thirds of the warming and, within the United States, they account for five-sixths. Due to their chemical structure, different types of fuel give rise to different amounts of carbon dioxide per ton burned and per unit of energy produced. Coal is the fossil fuel that produces the most carbon dioxide per unit of energy, followed by oil and gas. (Energy use is explored in detail in the next chapter.)
In addition to fossil fuel combustion, land-use changes contribute to the release of carbon dioxide into the atmosphere. These changes stem from clearing land for logging, ranching, and agriculture, or switching from agricultural to industrial or urban use. Vegetation contains carbon that is released as carbon dioxide when it decays or burns. Normally, lost vegetation would be replaced by regrowth, with little or no extra emissions because the replacement vegetation absorbs carbon dioxide from the atmosphere as it grows. However, over the past several hundred years, deforestation and other land-use changes around the world have contributed to one-fifth of the additional carbon dioxide in the atmosphere attributable to human activity, mostly through cutting down tropical forests.
This book concentrates on carbon dioxide emissions from fossil fuel use because these are the largest global source of greenhouse gases. However, it should be noted that, in addition to carbon dioxide, there are five other important greenhouse gases: methane, nitrous oxide, hydrofluorocarbons, per-fluorocarbons, and sulfur hexafluoride. The most significant of these are the first two. Methane emissions come primarily from agriculture, waste, coal mining, and natural-gas distribution. They can be a major component of greenhouse gas emissions in countries with strong agricultural economies. For example, as a by-product of their digestion, New Zealands forty-five million sheep and eight million cattle produce about 90 percent of that countrys methane emissions, which equates to over 40 percent of the countrys total production of greenhouse gases. Nitrous oxide is generated from agriculture, industrial processes, and fuel combustion. The other greenhouse gases are emitted from a small range of industrial processes and products. With the exception of methane, these other gases are much easier to control through technological change than is carbon dioxide.
Copyright © 2007 by Mayer Hillman with Tina Fawcett and Sudhir Chella Rajan. All rights reserved.
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