Climate Change

Weather is the state of the atmosphere at any specific time. Climate is the average weather pattern at a particular location. Weather and climate are usually described by such measures as temperature, precipitation, pressure, humidity, and wind speed and direction. In most parts of the world, these measures have been recorded for less than a century, so the actual historical record of direct observations is relatively brief compared with the human tenure of the earth. However, scientists are often able to extend the historical record by constructing synthetic climate data from other evidence such as tree rings, fossils, concentrations of plankton in ocean sediments, pollen in sedimentary rocks, and isotopes of carbon and oxygen in rocks and glacial ice. For example, narrow intervals between annual growth rings in trees and thin layers of organic material in lake sediments usually indicate cold dry conditions. Clues like these permit investigators to open a window on past climates.

Figure 109-2 illustrates trends in average global temperature during the past 10,000 years. Note that the global temperature has been in flux throughout this period. Not only has weather varied about long-term average conditions, but the averages themselves have changed over time. For example, during the most recent ice age (about 10,000 years ago), average global temperatures were approximately 6° C cooler than at present.³² In other words, a massive environmental change (the Wisconsin ice age) was connected with a relatively small climatic change. It is worthwhile remembering that regional changes in climate may or may not parallel global changes. For example, between 2600 and 2700 years ago—roughly at the time of Socrates and Confucius—North America was colder and wetter than was the continental average since the end of the Wisconsin glaciation, whereas conditions in Europe were warmer and drier. Fortunately, the climate has remained within a range that sustains life for most of the earth’s history, and the changes have occurred at very slow rates over thousands to millions of years.

FIGURE 109-2 Variations of mean global temperature during the past 10,000 years. Horizontal line represents present global average temperature.

(Modified from Henderson-Sellers A, Robinson PJ: Contemporary climatology, New York, 1991, Wiley.)

In spite of recent controversies regarding the accuracy of some climate science, a strong consensus exists among atmospheric scientists that global temperatures will rise significantly in coming decades.^50,85 One indicator of this trend is the fact that the 10 warmest years since 1861 all occurred after 1990.⁹⁸ Although the global climate system is enormously complex, two factors point toward warming. First, it is known that certain greenhouse gases warm the atmosphere by trapping short-wave radiation reflected from the earth’s surface when it is heated by solar radiation. Second, atmospheric concentrations of these gases, which include carbon dioxide, methane, and nitrous oxide, are steadily increasing. Normally, the materials in greenhouse gases pass through long biogeochemical cycles between natural sources and natural sinks. For example, sulfur enters the atmosphere as sulfur dioxide from volcanic eruptions and washes back to the oceans in the form of mildly acidic rainfall whose constituents are later incorporated into bottom sediments. Human activities can increase source loads (e.g., emissions) and reduce the absorptive capacities of natural sinks. In the case of carbon dioxide, the greenhouse gas about which there is most concern, both processes are at work simultaneously. Emissions of carbon dioxide have been increasing as energy-hungry societies burn petroleum hydrocarbons, coal, and wood. At the same time, forests that usually absorb huge amounts of atmospheric carbon dioxide continue to be cleared, although at rates that are less than was predicted in recent decades.

Atmospheric scientists are currently struggling to estimate how climate might change as greenhouse gases accumulate. For this purpose, they rely heavily on general circulation models (GCMs) that mathematically simulate the global climate system. The chemistry and physics of climate are complex and the models, although increasingly sophisticated, are still imperfect. Their accuracy is constrained both by the limits of current knowledge about the dynamics of the atmosphere and by the computational power of the most advanced supercomputers. They are also hedged with other limitations. For example, the present generation of GCMs is too coarse to provide more than a broad-gauge portrayal of atmospheric conditions in a lattice of regions over the earth’s surface. They are able to project some climate variables (such as temperature) with a high degree of accuracy, but there is still lower confidence in their ability to predict others (such as precipitation). They do not reveal storm systems that bring most of the weather to mid and high latitudes. They also do not incorporate the role of clouds as reflectors and absorbers of energy. They do not satisfactorily account for all of the carbon dioxide that is believed to have been liberated into the atmosphere through human activities. Nonetheless, many have considerable confidence in the accuracy of GCMs, because of their relative success in replicating present and past climates.

The Intergovernmental Panel on Climate Change (IPCC), a joint United Nations–World Meteorological Organization committee of leading Earth scientists, has synthesized existing research on climate change. They have completed four comprehensive assessments of the state of scientific knowledge and reached some sobering conclusions. A fifth is due to be published in 2014. In the most recent assessment (2007), it concluded that there is now “unequivocal” evidence that global average temperatures are increasing and projected to rise by between 1.1° and 2.9° C by 2100, even if greenhouse gas emissions are stabilized at 1990 levels. If emissions of greenhouse gases continue to increase, the report concludes that temperatures may rise by as much as 6.4° C by 2100.^50,85,86 The projected rate of warming is likely to be without precedent during the past 10,000 years on Earth.

While the IPCC estimates embody a consensus about global warming, the level of agreement declines as researchers attempt to forecast the resulting impacts, especially at regional and local levels. An enhanced greenhouse effect would have a greater effect on the global climate than would temperature alone. Solar radiation provides the energy that drives the climate system. The effects of a warmer atmosphere could produce a cascade of changes in many climate variables. For example, precipitation and evaporation would also be likely to increase, especially over high latitudes, but with strong regional variations elsewhere. Increasingly accurate climate projections for regional patterns of climate change have been developed in recent years.¹⁵

We will soon know a great deal more about regional patterns of climate change because a large number of studies that combine GCM data and other indicators of climate are being conducted.⁵

GCMs generally indicate that lower latitudes and lower elevations will be less affected by anticipated climate changes than will upper latitudes and higher elevations. However, the most recent generation of climate change impact simulations paint no simple pictures.^1,65 Different combinations of effects would be likely at different latitudes (Table 109-1). Most likely, a mosaic of regional and local changes will occur along a spectrum from strongly positive to strongly negative, depending on how, when, and where they occur. For example, some tropical islands, particularly in the Indian Ocean, are likely to experience heavy precipitation combined with more frequent severe storms and rising sea levels. Other islands, such as those in the Caribbean, are also likely to see increasing sea levels, but may experience a decline in summer rainfall. The net impacts of such changes are difficult to assess, but the experiences of Indian Ocean islands and coastlines during the massive tsunami of December 26, 2004, show just how vulnerable these regions already are to natural disasters. For the Andamans, the Maldives, the Seychelles, and other heavily populated low-lying islands of the Indo-Pacific Ocean, the results of sea level rise could be disastrous, while other places, such as high-standing islands of the Caribbean, could see offsetting agricultural benefits.⁶⁷

TABLE 109-1 Effects of Global Climate Change in Different Latitudes

More than any other factor, the rate of climate change is of concern to humans. General circulation models indicate that absolute changes in temperature will be smaller than those that have occurred at other times during the earth’s history. However, the anticipated climate changes would still occur at a rate and magnitude that are unprecedented in human experience. Whereas past changes usually occurred slowly enough for plants and animals to adapt or migrate, examples exist of mass extinctions following rapid change. Many scientists fear that today and in the future, insufficient time and undeveloped areas will be available for plants and animals to make similar adjustments.*

While changes of average climate would have important long-term consequences, variations in extreme weather might produce the most immediate and significant impacts.⁵⁶ Droughts, floods, and tropical cyclones are unusual events in today’s climate. If mean climates change, changes in the frequency and severity of these extremes would probably also occur and become manifest well before the permanent shifts could be confirmed.³¹ The geographic distribution of such events would also be affected. According to the IPCC, it is very likely that in the future, heat waves will be “more intense, more frequent and longer lasting,” while a decline in frost days and cold waves is projected over all land areas. The frequency of extreme precipitation events would also likely increase everywhere.³⁹ There would be increased incidences of drought and water shortages. This may also have profound impacts for the local environment, particularly in locations where the local flora and fauna may not be adapted to prolonged dry periods. Sea level rise is likely to increase on all coasts, except in a few locations where land uplift negates its impacts. This is likely to lead to increased erosion and coastal flooding, increasing pressures on sensitive coastal environments such as dunes and mangroves. Changes in both minimum and maximum temperatures experiences, particularly in the high latitudes and in upload areas, are likely to have important impacts on the ability of some plant species to survive. In other areas, these changes may have a positive impact on some species because of an increase in the length of the growing season. Overall, the impacts of global climatic change for wilderness areas will be complex and varied, influenced by a variety of local and regional factors as well as by global trends. As a result, natural hazards would be likely to pose increased risks to society. Moreover, exposure and vulnerability to extreme events would probably be exacerbated because populations at risk might respond to the new conditions on the basis of outdated information and assumptions.²³ We might find that our previous experience prepared us to “fight the last war” rather than the new one.

Stratospheric Ozone Depletion

The stratosphere is a distinct layer of the upper atmosphere that occurs between 14.5 and 56 km (9 and 35 miles) above the ground. It contains significant concentrations of ozone (O₃), a gas that is formed when solar radiation splits ordinary oxygen atoms.* The stratospheric ozone layer absorbs most of the ultraviolet (UV) radiation from space that would otherwise damage plant and animal species.

During the 1970s and 1980s, researchers discovered that stratospheric ozone was being lost and that the ozone layer was thinning to the point of disappearance, particularly in polar regions.^29,58 Chlorofluorocarbons (CFCs) were held to be at fault. For decades, these synthetic compounds had been manufactured in large quantities, mainly for use as aerosol propellants and refrigerants. Once CFCs escape into the atmosphere, they remain stable until reaching the stratosphere, where they decompose under the action of UV radiation. Chlorine atoms are released and bond with ozone atoms, breaking them down into oxygen and other products. As a result, the ozone shield is weakened or removed.

If the ozone layer is sufficiently depleted, intensity of UV radiation that reaches the earth’s surface could be significantly increased. This could have deleterious consequences for human populations and for plant and animal species. For humans, increased incidence of skin cancer, cataracts, and immune system suppression are three recognized effects of high UV exposure. Although humans might take precautions to protect themselves against UV radiation, such as reducing time spent outdoors, or adding sun blocks, glasses, and clothes, nonhuman species may not be able to make the necessary adaptations. Serious disruption of human and agricultural systems is possible.

During their winter seasons, the Antarctic⁶⁸ and to a lesser extent the Arctic^52,87,89 have experienced elevated levels of UV radiation. “Ozone holes” have been clearly traced to CFCs. An international agreement, the Montreal Protocol, was reached to phase out CFC usage by 1996. Much progress has been made toward that goal, but these compounds are still being produced in some developing countries and the substitute chemicals that were introduced elsewhere may also contribute to global warming.⁴⁷ In any case, chlorine atoms are extremely long lived in the stratosphere, perhaps persisting for 100 to 200 years. So there will continue to be some potential for additional ozone depletion in the decades to come.

Erosion of Biodiversity (See Chapter 110)

Loss of species or the habitats that support them is a controversial and potentially serious global problem that comes under the heading “erosion of biodiversity.” Biodiversity is not an agent of change like greenhouse gas buildup or ozone depletion. It is an index against which environmental changes can be assessed.⁸⁴ Like climate change and ozone depletion, biodiversity has a range of dimensions from global to local.³⁷ Two aspects of biodiversity that are of great importance are numbers and interconnections of species.

Estimates of the number of existing species are wide ranging because the state of knowledge about the planet’s biologic resources is both uneven and incomplete.⁸⁸ It is estimated that the earth hosts between 5 and 15 million species. About 1.75 million of these have been named.⁴⁹ Higher order mammals and birds in temperate ecosystems are well documented, but insects, worms and micro-lifeforms in tropical regions are far less known. In the United States, approximately 100,000 species are recognized²⁵ but only about one-fifth of these have been surveyed to date.⁸⁸

Paleobiologic research indicates that the number and type of species have varied greatly over time. New species evolve through adaptive genetic mutations, while others perish because of competitive pressures of natural selection. Emergence and disappearance rates depend on the speed and direction of environmental change and the ability of species to adjust. What is most troubling about the recent record is the disappearance of so many species. “Between 1600 and 1994, at least 484 species of animals and 654 species of plants (mostly vertebrates and flowering plants) became extinct. The rate of extinction in groups such as birds and mammals also increased dramatically during this period. Nearly three times as many species of birds and mammals became extinct between 1810 and 1994 (112 species) as were lost between 1600 and 1810 (38 species).”⁷³ Plant losses are presumed to have been much greater. On some oceanic islands, such as Hawaii, the disappearance of native animal species is almost total. Of 269 extinct Hawaiian species, most were either invertebrates (135) or plants (105). A majority of the rest are birds (15) and land snails (11).⁸⁸ Commercial forestry and fishing have proved particularly injurious to biodiversity because they harvest desirable species and destroy undesirable species at the same time.³⁶ Agriculture and animal husbandry also contribute to species extinctions, especially by modifying the habitats that support biota. Particular concerns have been expressed about threats to tropical forests and the near extinction of some marine species like the northern cod, blue whale, and leatherback turtle. However, the problem is general in scope and may be most important for the “noncelebrity” species that do not elicit much human compassion.

It is estimated that about 32% of all U.S. species are now under serious pressure, sometimes to the point of threatened extinction (Table 109-2).⁸⁸ However, the picture varies widely among particular groups of species (Table 109-3). Denizens of freshwater ecosystems, such as shellfish, crustaceans, amphibians, and fish, are far more likely to be in danger than are flowering plants, conifers, mammals, and birds. Likewise, on the U.S. mainland, loss of biodiversity is more acute in Sunbelt states and east of the Mississippi River than in states of the northern Great Plains and the northern Rocky Mountains.

TABLE 109-2 Percentage of U.S. Species at Risk

TABLE 109-3 U.S. Species Groups at Risk

For many people, protection of threatened species is a moral imperative. For others, it is a luxury. Quite apart from moral issues, the rising rate of species extinction has practical implications.⁷⁴ For example, loss of the planet’s genetic stock hampers the search for wild strains of domestic crops that are resistant to pests and diseases that plague high-yield domestic varieties. The so-called Green Revolution that has helped to alleviate world hunger in recent decades owes much of its success to the introduction of resistant wild genetic strains into commercial agriculture.

Biodiversity is also important in the stability of global ecosystems. For example, the extent to which entire species can be eliminated from an ecosystem before it collapses is unknown. Likewise, the extent to which some nominally “wild” species may thrive under human management, while others succumb, is hotly debated.²⁷ Most ecologists believe that ecosystems containing a wide diversity of organisms are more resilient to change than are those with few species. Regardless of the degree of resilience, biodiversity and environmental change may be connected by negative feedback relationships. Environmental change may lead to a loss of biodiversity that in turn produces lowered resistance to pressures for further change.

Despite intuitive, theoretical, and case study arguments in favor of preserving biodiversity, it has been difficult to agree on standardized measures of biodiversity or its loss. Deforestation of South American rainforests is a case in point. The Amazon Basin is one of the world’s premier wilderness regions and is also regarded as its most important source of biodiversity. Perhaps impelled by dramatic and widely publicized reports of forest clearances by ranchers, homesteading farmers and mineral firms in Brazil during the late 1980s, levels of international concern about the loss of biodiversity in Amazonia have been high. But, as in most developing countries, comprehensive and reliable data on Brazilian deforestation are difficult to secure and interpret.^83,99

Given the foregoing uncertainties, it is difficult to predict future rates of loss of biodiversity. The best available estimates suggest that about 3.5% of today’s bird species will likely become extinct by the year 2050, together with most large marine predators and much of species richness of freshwater ecosystems.⁴¹

Population Growth

Human population is one of the primary driving forces behind contemporary environmental change. Beginning with the Reverend Thomas Malthus (1766-1834), many people have argued that rising populations must eventually deplete resources and degrade environments because the earth is, for all intents and purposes, a closed system.⁴⁶ In the absence of interplanetary space travel on a scale impossible at present, to destinations that are now unknown and perhaps nonexistent, the earth is our only home. This does not mean that it will be impossible for the earth to hold additional human populations. If the record of the past four centuries provides a demographic lesson, it is that the global carrying capacity is highly elastic up to some, as yet unreached, limit.¹⁶ Leaving aside the argument that human ingenuity can make possible the support for larger populations indefinitely, clearly from the perspective of burdens on the physical environment, how people live is more important than the number of people. All other things being equal, richer societies place heavier burdens on the physical environment than do poorer ones. For example, the United States, with just 5% of the global population, consumes approximately 25% of the world’s energy resources.¹⁸

The global population has undergone unprecedented growth in the past several centuries (Figure 109-3). By 1800, the earth’s population was approximately 1 billion. By 1920 it was 2 billion. Three billion was reached in 1960, and the present estimate is more than 5 billion. The United Nations estimates that there will be somewhere between 6.3 and 8.9 billion people on Earth by 2050. Most of the new growth is likely to occur in developing countries of Asia, Africa, and Latin America (Table 109-4). The recent experience of China suggests that the process of development can itself perpetuate or increase historical rates of population growth, at least until economic conditions improve significantly.

FIGURE 109-3 Global population (1700-2020).

(Modified from Demeny P: Population. In Turner BL II, editor: The earth as transformed by human action, Cambridge, UK, 1990, Cambridge University Press.)

TABLE 109-4 Average Annual Percentage Rates of Population Increase

The composition of future populations is an increasing concern of governments and individuals. In places like Japan and Eastern Europe, natural increase is now well below the rate necessary to replace existing populations, whereas in the United States increasing numbers are maintained largely by immigration. As a result, the fraction of national populations that is more than 65 years old is growing rapidly in the more developed world. Meanwhile, increasing expertise in genetic manipulation holds out the prospect of significantly longer life spans for populations that can afford the kind of scientific research and medical care that will make this possible. In other words, some parts of the world’s population will become increasingly healthier and older, while others may remain caught in a cycle of short sickness-prone lives followed by early deaths. Quite apart from the staggering societal impacts that such a change would produce, the implications for wilderness are considerable. For those who can be assured of longer lives, the quality of life experience, including the quality of their environments, may become of foremost importance. Wilderness areas would be among the most cherished places and decisions about their future all the more portentous. Among developing countries, a different future might obtain, perhaps dominated by intense pressure to convert all available resources into supports for survival. Although such scenarios are not difficult to envisage, they carry with them a danger of indulging in stereotypical dichotomizations that ignore possibilities for a range of more nuanced outcomes.

Today the greatest uncertainties about future populations pertain to rates of migration and the composition of families.¹⁷ If current patterns of migration continue, the lion’s share of the migrants will end up in large countries like the United States, India, Pakistan, France, and Germany where, depending on their internal destinations, they may add to the burden of users on existing wilderness areas.

Pollution

Unwanted by-products of production and consumption that exceed the absorptive capacity of the environment are known as pollution. Pollution comes in many forms, including solid physical materials, liquid chemical compounds, and energy (e.g., thermal pollution). Some pollutants (such as certain isotopes of plutonium) are highly toxic even in small amounts. Many materials that are beneficial in small amounts can be deleterious in large quantities. For example, phosphorus is a nutrient that limits biologic productivity in coastal and marine ecosystems. Small amounts of phosphorus can increase algal growth at the bottom of marine food chains. But when larger amounts of phosphorus-rich runoff from fertilizers or septic systems enter these environments, the entire population of algae can begin a period of explosive growth (“bloom”). Extensive blooms can produce “red tides” or “brown tides.”¹⁴ This occurs when algae prevent light from penetrating coastal waters and decomposition of dead algae consumes dissolved oxygen. Large fish kills are a frequent result.

The preferences of people for quick and convenient disposal of pollutants into available environmental sinks (such as soil, streams, groundwater, oceans, and atmosphere) have sometimes been validated by incomplete science. For decades, in the United States and elsewhere, scientists advised policy, makers that “the solution to pollution is dilution.” As a result, physical and chemical wastes have been released into environments that had finite capacities for absorbing them. Once the absorptive capacities were reached, a variety of serious problems occurred. These included biologically “dead” rivers (such as Cleveland’s Cuyahoga River), “dead” lakes (such as Lake Erie), and “dead” seas (such as the sewage sludge dumping ground in the New York Bight off the coasts of New Jersey and Long Island). Although some of these conditions can be reversed, the processes are slow, costly, contentious, and often incomplete. Also, a growing body of evidence suggests that the aggregate effect of pollution may be jeopardizing the functioning of fundamental Earth systems. The buildup of atmospheric carbon dioxide is an excellent example of this process.

Despite a large volume of evidence, the effects of pollutants on receiving environments are not fully known.¹⁸ This is partly because of a lack of scientific knowledge about the normal (unpolluted) functioning of some environments, such as deep oceans and tropical forests. The sheer volume and variety of materials released into the environment and their interactions complicate the study of effects of any single pollutant. Sometimes the effects of pollutants are subtle, long delayed, and far removed from the point of origin, making it difficult to connect causes and consequences. Sometimes experts disagree about evidence of pollution impacts collected in the field and acquired from laboratory experiments. Even the impacts of well-studied events like the Exxon Valdez tanker grounding are in dispute.^9,64 Nonetheless, there is broad consensus that the absorptive capacity of receiving media is not inexhaustible and that pollution is a growing world problem pushing society against the limits of environmental resilience.