Atlas 3 introduction-print


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Atlas 3 introduction-print

  1. 1. 673Human Impacts on the PlanetVisualising Change over TimeHuman interactions with the environmentleave many traces. For much of humanhistory, human impact on the Earth’ssurface has been relatively minor. In thelast several hundred years, however, thatimpact has grown tremendously. Changebrought about by human activities can nowbe objectively measured; it can even beseen from space. A study by the NationalAeronautics and Space Administration(NASA 2003a) known as The Human Foot-print (Figure 3.1) is a quantitative analysisof human influence across the globe thatillustrates the impact of people and theiractivities on the Earth.Evidence of change is not always vis-ible on the landscape. Change also occursin the atmosphere, in the soil, and in theoceans and other water bodies. In theseenvironments, evidence of change canstill be “seen,” however, by detecting andmeasuring things such as rising averageglobal temperatures, the concentrations ofcertain gases in the atmosphere, and vari-ous chemical contaminants in water.Change alone is not the only problem.It is the degree to which human activitiesare changing the Earth that is also causefor growing concern. For instance, theresults of a recent ten-year study concern-ing the ecological effects of industrializedfishing in the world’s oceans reveals thatlarge predatory fish species includingtuna, marlin, sharks, cod, and halibut havedeclined by an estimated 90 per cent frompre-industrial levels (Myers and Warm2003). Furthermore, the average size ofsurviving individuals among these speciesis only one-fifth to one-half what it waspreviously.The composition of the Earth’s atmo-sphere is also undergoing rapid change.Since life began on Earth, changes inclimate have ordered the distribution ofMap of the Human FootprintFigure 3.1: The Human Footprint is a quantitative analysis of human influence on the Earth’s surface. In thismap, human impact is rated on a scale from 0 (minimum) to 100 (maximum) for each terrestrial biome. Thecolor green indicates areas of minimal impact while purple indicates areas of major impact. Credit: Scott, Michon2003. The Human Footprint. NASA: Socioeconomic Data and Applications Center. Source: Topfoto
  2. 2. 68organisms and their behavior. Today,increases in atmospheric concentrationsof greenhouse gases are expected to causemore rapid changes in the Earth’s climatethan have been experienced for millennia(Figure 3.2). At least some of the increaseglobally is due to human activity, andcertainly, local impacts such as urban heatislands have profound effects on regionalclimatic conditions. As shown in Figure 3.2,waste generation and disposal is one of theways in which humans contribute green-house gases to the atmosphere.An emerging global impact issue is thatof electronic or E-waste—a collective termfor discarded electronic devices. Over thepast decade, E-waste has become one ofthe world’s fastest growing waste streamsand—due to the presence of lead, mer-cury, brominated flame retardants, andother hazardous substances—one of themost toxic. The disposal of computer wastein particular is becoming a difficult issue asmillions of computers and other electronicdevices are rapidly becoming obsolete aseach year the industry produces ever-great-er quantities of less-expensive equipment.There are an estimated 300 million obso-lete computers in the United States, withfewer that ten per cent destined for recy-cling each year. Even when a computer issold to a secondhand parts dealer, however,there is a good chance it will end upin a dump in the developing world(Figure 3.3).The Earth’s forests are also underpressure. Tropical forests are now beingsubjected to the same heavy exploitationas were temperate forests a few genera-tions ago. Pressures from logging, mining,hydropower, and a hunger for land areFigure 3.2: The disposal and treatment of waste canproduce emissions of several greenhouse gases thatcontribute to global climate change. Even the recy-cling of waste produces some emissions, althoughthese are offset by the reduction in fossil fuels thatwould be required to obtain new raw materials. Bothwaste prevention and recycling help address globalclimate change by decreasing greenhouse gas emis-sions and saving energy (Environmental ProtectionAgency). Source: Topfoto
  3. 3. 69leading to large areas of forest being con-verted to serve other purposes. The integ-rity of forest ecosystems is being affectedas the timber and paper industries removevast areas of mature tropical and temperateforests. As a consequence, forest ecosys-tems lose their ability to support complexbiodiversity and thousands of plant andanimal species disappear forever.Several globally significant environ-mental trends that have occurred between1980 and 2000 may also be contributing toloss of forest ecosystems, including globalwarming (the two warmest decades onrecord are the 1980s and 1990s), three in-tense El Niño events, changes in cloudinessand monsoon dynamics, and a 9.3per cent increase in atmospheric CO2. Al-though these factors, along with others, arethought to exert their influence globally,their relative roles are still unclear.An observed decline in tropical cloudcover is probably one of the more impor-tant recent climatic changes, althoughnone of the existing climate models canaccurately simulate this effect. It is knownthat continued reductions in tropical cloudcover, if accompanied by reduced rainfall,will have profound implications for tropicalecosystems in terms of water stress, produc-tivity, ecological community composition,and disturbance patterns.Images of ChangeVarious types of ground-based instruments,together with in situ surveys and analyses,can measure many of the changes beingbrought about on the Earth as a result ofhuman activities. But such changes canalso be observed—in more detail and witha “big picture” perspective—from space byEarth-orbiting satellites that gather imagesof the Earth’s surface at regular intervals.The Landsat series of Earth-observingsatellites has compiled a data record of theplanet’s land surfaces that spans the pastthirty years and continues today.By comparing two images of the samearea taken ten, twenty, or even thirty yearsapart, it is often easy to see human-inducedchanges in a particular landscape. Fewplaces remain on our planet that donot show at least some impact fromhuman activities.The focus of this chapter is a set ofspecific case studies in which satellite im-ages, taken at different times, are pairedso as to reveal changes and human impactson the atmosphere, oceans and coastalzones, freshwater ecosystems and wetlands,forests, croplands, grasslands, urban areas,and the tundra regions.The changes that we see in pairs ofsatellite images should make us cautious.Some are positive changes. But many moreare negative. These images could be seenas warning signs. At the least they shouldprovide us with food for thought andprompt us to ask pointed questions: Howcan we be more protective of our environ-ment? How can we use the environment inways that will not reduce the ability of theEarth to support us in perpetuity?Figure 3.3: The high tech boom has been accompanied by E-waste, which rep-resents the largest and fastest-growing type of manufacturing waste product.Recycling E-waste involves major producers and users, and the shipping ofobsolete equipment and other products to Asia, Eastern Europe, and Africa whererecyclers, such as the people in this photo, are exposed to toxic substances.Source: Basel Action Network