Chapter 23 focuses on global-scale processes and phenomena, including large-scale weather systems and global change induced by humans. We are the only species that exerts global-scale influences on the environment.
The earth is wrapped in an atmospheric envelope that makes the biosphere a hospitable place for life as we know it. The earth's atmosphere reduces the amount of ultraviolet light reaching the surface. The atmosphere also helps to keep the surface of the earth warm through the greenhouse effect. The surface of the earth is kept warmer than it would be by the greenhouse gases, including water vapor, methane, ozone, nitrous oxide, chlorofluorocarbons, and carbon dioxide.The El Niño Southern Oscillation is a large-scale atmospheric and oceanic phenomenon that influences ecological systems on a global scale. The El Niño Southern Oscillation is a highly dynamic, large-scale weather system that involves variation in sea surface temperature and barometric pressure across the Pacific and Indian Oceans. During the mature phase of an El Niño, the sea surface in the eastern tropical Pacific Ocean is much warmer than average and the barometric pressure over the eastern Pacific is lower than average. El Niño brings increased precipitation to much of North and parts of South America and drought to the western Pacific. Periods of lower sea surface temperature and higher than average barometric pressures in the eastern tropical Pacific have been named La Niñas. La Niña brings drought to much of North and South America and higher than average precipitation to the western Pacific. The variation in weather caused by the El Niño Southern Oscillation has dramatic effects on marine and terrestrial populations around the world.Human activity has greatly increased the quantity of fixed nitrogen cycling through the biosphere. For millions of years, the only organisms that could fix nitrogen were nitrogen-fixing bacteria and some actinomycete fungi. The total amount of nitrogen fixed by these historical sources is approximately 130 Tg N per year. The nitrogen now fixed as a consequence of human activity is about 135 to 145 Tg N per year, more than all nonhuman sources of fixed nitrogen combined. Large-scale nitrogen enrichment may threaten biological diversity by creating environmental conditions favorable to some species at the expense of others. Rapid changes in global patterns of land use threaten biological diversity. Human activities, mainly agriculture and urbanization, have significantly altered one-third to one-half of the ice-free land surface of the earth. A widely cited example of land cover change is tropical deforestation. From 1978 to 1988, the rate of deforestation in the Amazon Basin of Brazil averaged about 15,000 km2 per year. By 1988, the total area deforested within the Amazon Basin was 230,000 km2. By adding in edge effects and the effects of isolation, the area of Amazonian forest affected by deforestation increases from 230,000 km2 to 588,000 km2. The global rate of tropical deforestation from 1978 to 1988 was about 30,000 km2 per year. Massive deforestation has also occurred outside of the tropics. Because of the negative effect of reduced habitat area on diversity, these massive land conversions present a major threat to global biological diversity. Human activity is increasing the atmospheric concentration of CO2, which may be increasing global temperatures. Analyses of air trapped in ice shows that the concentration of CO2 in the atmosphere has varied widely during the last 160,000 years and closely parallels variation in global temperatures. High levels of atmospheric CO2 have corresponded to higher global temperatures. The buildup of atmospheric CO2 during the past two centuries has reached levels of atmospheric CO2 not equaled in the past 160,000 years. There is little doubt that the present level of CO2 in the atmosphere is strongly influenced by burning of fossil fuels. Increases in atmospheric CO2 concentration are likely to affect global climate and the structure and processes of ecological systems from populations through landscapes.
Cooperative research networks aid global ecology. The present possibility of rapid climate change poses a substantial challenge to the scientific community. Studying ecology at a global scale requires that scientists develop new tools and approaches. New devices, often employing the most recent technological developments, are becoming more and more common in the tool kit of ecologists. However, some of the most important developments required for global-scale research may involve changes in the "culture" of science. The complexity and large scale of global change requires that scientists work in multidisciplinary, national, and international teams. International networks of scientists now work on global-scale ecological problems in a research environment that emphasizes information sharing and a team approach to research.
