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Beyond the Planet's 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 earth's 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 earth's surface is partly absorbed by certain gases in the atmosphere and some of this is returned to earth. This infrared radiation further warms the planet's 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 Zealand's forty-five million sheep and eight million cattle produce about 90 percent of that country's methane emissions, which equates to over 40 percent of the country's 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.
Carbon Dioxide Emissions
Concentrations of carbon dioxide in the atmosphere have been increasing since the Industrial Revolution. In 1750, there were 280 parts per million (ppm) but by 2005 the figure was 380 ppm, a rise of over one-third. As can be seen in figure 1, below, much of this staggering increasemeasured at Mauna Loa, Hawaii, the meteorological station with the longest records in the worldhas taken place since 1959. From 1997 to 1998, there was an increase of 2.87 ppm, the largest single yearly jump ever recorded.
Data have been obtained from measurements of air that has been trapped in ice over thousands of years. These reveal that today's carbon dioxide concentration has not been exceeded in the past 420,000 years and probably not during the past 20 million years. As well as the level, the rate of increase over the past century is unprecedented. Compared to the relatively stable carbon dioxide concentrationsin the preceding several thousand years, there were relatively minor fluctuations around the 280 ppm figurethe increase during the industrial era, and particularly the most recent increase, is proving catastrophic.
This phenomenon is perhaps unsurprising. Fossil fuels contain the energy stored from the sun that took hundreds of thousands of years to accumulate, yet within the space of a few generationsa mere blink of the planet's life so farwe are burning it: Figure 2 shows the dramatic and accelerating growth in carbon emissions from fossil fuel use, which is the major source of the accumulating concentrations. Half the total emissions since 1750 have occurred since the mid-1970s, with annual emissions doubling since the mid-1960s and trebling since the mid-1950s. Emissions of carbon dioxide from fossil fuel burning rose from about 10 million tons of carbon a year in 1800 to around 7 billion tons at present, which is 700 times as much. Future scenarios suggest that, unless dramatic policy changes are made, annual emissions will rise substantially and inexorably. At the extreme, they could be five times their current level by 2100, resulting in the 10°F or so of global warming referred to earlier. In fact, since our atmosphere and oceans take a long time to warm up (and cool down), the effects of these higher emissions could get even worse over time.
At the start of this century, total annual global emissions from fossil fuels amounted to more than 7,000 million metric tons of carbon (MtC). Emissions from North America (United States and Canada) made up over a quarter of the total, and those from Western Europe accounted for about one-tenth. The United States continues to have the highest fossil fuel-related emissions, reaching 1,580 million metric tons of carbon in 2003. This represents nearly a quarter of the world's total. U.S. emissions are two-thirds higher than those of the world's second-largest emitter, the People's Republic of China, and almost seven times those of the whole African continent. In general, emissions from the United States have risen each year since 1900, with the exception of brief periods in the 1930s and 1980s. Since 1990, fossil fuel emissions have risen between 1 and 2 percent each year. Chapter 2 explains in detail the patterns of changing energy consumption and the underlying trends that have driven this upward and led to the increasing emissions.
Each person in the world is engaged in fossil fuel-based activity that results in the emission of, on average, 1.1 metric tons of carbon. If these emissions are compared by country, the differences are stark. Near the top of the league is the United States, at 5.5 tC per person, around five times the global average. In the fifteen Western European members of the European Union, they are 2.3 tC. The developing nations currently contribute much less, with China's emissions at 0.7 tC per person, Indonesia's at 0.4 tC, and India's at 0.3 tC. Afghanistan is at the bottom of the emissions league, at 0.01 tC, just one one-hundredth of the global average and less than one five-hundredth of that of the average U.S. citizen.
How Is the Climate Changing?
Figure 3 shows how the global average surface temperature (over sea and land) has risen from 1850 to the present. Because temperatures vary naturally from year to year, climate scientists must compare several years' temperature records with long-term averages to be sure the suspected temperature change is significant. The data are set out in terms of the "anomaly"that is, the difference between each year and the average temperature in the period 1961-90. Before 1978, it was generally colder, with all later years warmer. These data are shown in the figure in degrees Celsius, not Fahrenheit: A rise of 0.47°C is equivalent to 0.8°F.
Global temperature, established from millions of individual measurements taken from around the world, rose by about 1.1°F during the last century, with two-thirds of this warming occurring since the 1970s. The 1990s was the warmest decade, with 1998 being the warmest year since 1860, when world temperature measurements were first recorded. Scientists at the University of East Anglia in the United Kingdom, in one of the most comprehensive studies to date of climatic history, have confirmed that the planet is now warmer than it has been at any time in the past 2,000 years. And there is no sign of this trend reversing: nineteen of the twenty hottest years in the past 150 years have occurred since 1980, and 2005 was the warmest year on record in the Northern Hemisphere. Worldwide, temperatures on land have warmed more than the oceans.
The United States reflects these trends. Observations from over twelve hundred weather stations across the country have shown that the average temperature rose by almost 1°F during the twentieth century, with annual temperatures in the coastal Northeast, the upper Midwest, the Southwest, and parts of Alaska experiencing increases four times that average. The largest observed warming has been seen in winter.
Other Climate Changes
Rising temperatures increase the amount of energy in the atmosphere, and this has consequential effects: Climate models predict changes in rainfall amounts and patterns, and a rise in the occurrence of storms, heat waves, and other extreme events. Some of these changes, including periods of sustained drought from higher than average temperatures and well below average rainfall, have already been experienced in the United States and around the world. The most populated state of Australia has recently experienced four years of drought. When persistent droughts occur, there is little reserve water to weather them, leaving people, livestock, and crops at risk. The growing season is then reduced or even lost completely. Because of this, food production in some parts of the developing world is already in decline. The well-known variability of the climate can make it difficult to ascertain that any individual event is unusual and specifically caused by climate change. But the accumulating evidence from studies over the last forty years makes it highly unlikely that the data can be interpreted as the outcome of a natural cycle uninfluenced by human activity.
In the United States, signs of water stress that used to be limited to the West are now increasingly common in the Eastfrom dried-up rivers to shrinking lakes and falling water tables. On the other hand, average precipitation has increased by 5 to 10 percent over the last century, with much of that due to an increase in the frequency and intensity of heavy rainfall. Precipitation increases have been especially noteworthy in the Midwest, southern Great Plains, and parts of the West and Pacific Northwest.
Of particular concern has been the increased frequency and intensity of extreme events, such as storms and hurricanes, as these tend to have severe effects on people and on the man-made environment as well as the natural environment. This concern was intensified as a result of the very active hurricane season and particularly the severe impact of Hurricane Katrina on New Orleans and the surrounding area in 2005. Indeed, 2005 was the most destructive year on record.
Although the number of tropical storms and hurricanes has remained roughly constant in the last thirty years, there has been an increase in their intensity, with a rising proportion having wind speeds above 130 miles per hour. This has been shown to be linked to recorded increases in sea-surface temperatures. Some scientists have established a direct link between climate change and the increasing intensity of hurricanes. Global climate change may also affect other weather systems. El Niño is a complex, natural change in weather patterns that occurs every few years, affecting the equatorial Pacific region and beyond. It caused worldwide damage valued at $32 billion in 1997-98. At present, there is a suspicion, though not yet proof, that El Niño has been made worse by global warming.
Climate science, like any other science, is characterized by intense debates that range from the role of clouds and aerosols in calculating the magnitude of the greenhouse effect, to the difficulty of establishing the extent to which observed climatic changes are attributable to human activity. A small but vocal group of lobbyists, called "climate skeptics" by the media, has challenged the consensus on climate change and its causes. Typical of the more influential of these was a senior U.S. government official describing man-made global warming as "the greatest hoax ever perpetrated on the American people." However, groups like the Intergovernmental Panel on Climate Change (IPCC), the American Geophysical Union, the U.S. National Academy of Sciences, and ten other related leading world bodies support two critical scientifically determined judgments: first, that global warming is happening, and second, that much of the observed warming is human induced. They admit that it is difficult to predict some aspects of this human-induced climate change, such as exactly how fast it is occurring, exactly how much it will change, and exactly where the changes will take place.
The skeptics, on the other hand, who have tended in the past to deny both judgments, are now largely in the habit of denying just the second one, on the grounds that climate science itself is too complex for us to be sure that humans are largely responsible for climate change. The Union of Concerned Scientists, a watchdog group of scientists and citizen advocates, has examined a list of the more prominent of these skeptic groups. Its analysis reveals that the great majority either belong to or are actively sponsored or funded by organizations such as the fossil fuel industries, which have a commercial interest in denying the reality of climate change. Though in a very small minority, they are much better known in the press than in scientific journals, suggesting that they have not been able to prove their case using established scientific methods.
Copyright © 2007 by Mayer Hillman with Tina Fawcett and Sudhir Chella Rajan. All rights reserved.