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A Vision for the International Polar Year 2007–2008 3 Understanding Change in the Polar Regions “When we try to pick out anything by itself, we find it is tied to everything else in the universe.” JOHN MUIR From the collapse of some fisheries to the disintegration of sea ice and floating ice shelves, recent change in the polar regions has captured the attention of the American public. Scientists predict the environment will continue to change in response to increasing levels of greenhouse gases in the Earth’s atmosphere, with particularly high sensitivity in the polar regions (IPCC, 1998, 2001). The primary scientific issues are (1) to understand the nature of changes we are experiencing today within the context of the past, in order to discriminate between anthropogenic and natural variability and (2) to understand global linkages and the coordinated impact of changes on climate and weather patterns, ecosystems, and human endeavors across the planet. The Earth has strongly linked systems, and it is important to understand mechanisms and impacts of changes in the polar systems. Rapid changes, in particular, can be devastating if they exceed the timescale of adaptability, and there is compelling evidence from past climate records that the environment is capable of changing abruptly, on timescales of ten years or less (NRC, 2002). HUMAN-ENVIRONMENT DYNAMICS Studies of a wide range of issues related to the human dimensions of change in the polar regions stand to make important International Polar Year contributions. These human-environmental linkages directly involve the people who live in northern regions in many ways, but also involve people all around the world. For example, at this global level, changing environmental conditions—including the frequency and duration of severe weather events such as storms, precipitation, or drought—can have a range of impacts on human daily activity in temperate as well as polar regions. The Arctic Oscillation/North Atlantic
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A Vision for the International Polar Year 2007–2008 Oscillation, the El Niño-Southern Oscillation, and the Antarctic Oscillation are all multiyear low-frequency patterns of atmospheric and oceanic circulation that have effects ranging from major flooding in some regions to droughts and fires in others (NRC, 2002). Changing environmental conditions affect systems we use every day, from the impact of snow on the mobility of vehicles and freeze/thaw destruction of roadways to icing of aircraft wings, and these pose engineering challenges. Permafrost has received much attention recently because surface temperatures are rising in most permafrost areas of the Earth, bringing some permafrost to the edge of widespread thawing and degradation. In the Arctic, thawing permafrost due to warming is resulting in the loss of soil strength. This has already caused the failure of roadways, runways, and pipelines Permafrost, found mainly in the polar regions, is ground that has a temperature lower than 0°C continuously for at least two consecutive years. In the continuous zone, permafrost is found almost everywhere, while in the discontinuous zone, permafrost is found intermittently. In the sporadic zone, permafrost is found in isolated, small masses, and in the isolated zone permafrost is infrequently found. SOURCES: International Permafrost Association and UNEP Global Resource Information Database.
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A Vision for the International Polar Year 2007–2008 and is causing the foundations of some structures to collapse (ACIA, 2004). These observed and predicted changes in permafrost make it important to monitor permafrost dynamics (particularly its temperature through boreholes) so that we become more skilled at assessing and projecting possible impacts on ecosystems and infrastructure. Another possible human-environment interaction linked to environmental change relates to changing ice conditions in the Arctic. Continued loss of summer sea ice could increase ship access in the Northwest Passage along the northern shores of Canada and the Northern Sea Route (Northeast Passage) along the Arctic coast of Russia (INSROP, 1999), with implications for commerce and national security (ONR, 2001). Due to large-scale atmospheric flow patterns, continued global warming may result in cooling in some north Atlantic regions (Alley, 2000). One clear illustration of a polar-global linkage with a direct human impact is the transport of contaminants from industrial regions to the Arctic. The discovery of “Arctic haze” in the 1970s and early 1980s (Barrie, 1986) demonstrated that the Arctic is not a pristine environment isolated from human activity elsewhere but rather a region well connected to natural and anthropogenic sources of chemicals by winds, ice movement, and marine currents. The study of this phenomenon led serendipitously to the discovery of ozone depletion in the troposphere in the Arctic marine boundary layer at polar sunrise (Oltmans, 1981; Bottenheim et al., 1986). It has only recently been realized that natural reactions in snow can have important effects on the troposphere (Dominé and Shepson, 2002). For example, ozone is perturbing the biogeochemical cycle of mercury, and tropospheric ozone depletion chemistry is likely to have a significant impact on near-surface radiative transfer, affecting the air-snow-sea exchange of biologically mediated compounds (Lu et al., 2001; Shepson et al., 2003). The transport of contaminants such as heavy metals, pesticides, and persistent organic pollutants to the north has direct impacts on residents. Fish caught in remote northern lakes and oceans contain unexpectedly large amounts of mercury (AMAP, 2002). Observations in the Arctic showed evidence of anthropogenic pollution as early as the 1940s. Figure 3.1, from McConnell et al. (2002), shows the record of atmospheric pollution by lead as recorded in a Greenland ice core. A clear increase in lead is seen during the Industrial Revolution. This is followed by a decrease toward preanthropogenic levels when the use of unleaded gasoline became widespread and air quality laws were put into effect. Human activities do impact the environment on a large scale, and through wise policy decisions, improvements are possible. Future changes in climate could lead to spatial and temporal changes in transport patterns and deposition of pollutants. Complex interactions between the atmosphere, oceans, biota, and snow cause transformations that are not understood. International collaboration will promote understanding of linked physical-chemical-biological interactions occurring in the atmospheres, oceans, permafrost, snow and ice, and human food chains in the polar regions. Beyond these physical impacts of the changing environment on people, there is strong concern about how rapid social and economic changes continue to affect indigenous cultures in the northern high latitudes. Some of these impacts are undoubtedly positive: satellite communications now link even the most remote northern communities to the rest of the world, allowing, for example, doctors to render care using telemedical technologies and northern hunters to travel with increased safety using global positioning systems as navigation aids. In addition to the many benefits of advances in technology and communications, rapid cultural change has also been
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A Vision for the International Polar Year 2007–2008 FIGURE 3-1 Continuous, high-resolution lead flux and crustal enrichment since 1750 from a 1999 ice core from Summit Greenland. Trends of increasing levels during the Industrial Revolution were reversed after air quality laws were put into effect. SOURCE: McConnell et al., 2002. accompanied by problems such as alcoholism, drug use, and other social disorders in some northern communities, as it has in lower latitudes. There are concerns that environmental or social change could lead to problems with food safety and availability and circumpolar health in general. Understanding societal changes in the polar regions can provide lessons relevant to the broader science community as well as to the residents of lower latitudes who also face the impacts of social and environmental changes. More research is needed to better understand how new technologies can help northern indigenous peoples preserve their own cultural heritage, rather than allowing the same technologies to simply play a homogenizing role. The firsthand impacts of environmental change are being felt by Arctic subsistence communities, such as those who hunt whales on the Alaskan North Slope, practice reindeer husbandry in Finland and Russia, and hunt caribou in northern Canada and Alaska (Krupnik and Jolly, 2001; Putkonen and Roe, 2003). Coastal erosion caused by unusual and irregular storm patterns and rising sea level have threatened coastal communities in the Arctic. U.S. government agencies have taken emergency actions to cope with the increased beach erosion and relocation of some communities in northern Alaska due to sea-level rise. Northern communities in permafrost regions will face significant engineering and infrastructure challenges if the permafrost thaws. Modern technologies also can be affected by changes in the environment. The solar processes that produce disturbances in the Earth’s space environment (space weather) affect high-frequency communications, including cell phones, global positioning systems, and power systems. Changes in ocean circulation and temperature patterns have an impact on acoustic propagation pathways for subsea communications. Changes in the patterns and severity of winters on land affect many modern
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A Vision for the International Polar Year 2007–2008 NASA satellite imagery analyzed at the University of Colorado’s National Snow and Ice Data Center revealed that a section of the Larsen B ice shelf on the eastern side of the Antarctic Peninsula shattered and separated from the continent in early 2002. A total of about 3,250 square kilometers disintegrated in a 35-day period, an area larger than the state of Rhode Island (2,717 square kilometers). This is the largest single event in a series of retreats by ice shelves along the peninsula over the last 30 years. SOURCE: NASA. technologies, from snow and ice impacts on ground travel to ice formation on aircraft wings (NRC, 2004a). Interdisciplinary science holds great promise for understanding the strong links between rapid changes in environment, technology, and the actions of individuals and societies. Environmental, technological, and societal changes in the polar regions are occurring now, and understanding those changes can provide lessons relevant to all nations. The IPY offers many venues to study these issues internationally and to develop methods for resilience. CHANGES IN THE POLAR REGIONS IN RECENT TIMES Large-Scale Environmental Change The character of recent changes in the polar regions (Table 3.1) results from the unique environmental conditions. Both polar regions have vast relatively permanent ice sheets that serve as massive freshwater reservoirs. In contrast, sea ice is typically only a few meters thick and is highly dynamic from year to year. Seasonal and interannual variations of sea ice can alter surface air temperatures in excess of 20°C locally, with far-reaching consequences. Surface warming melts ice and snow-covered surfaces, which normally are highly reflective, increasing the absorption of sunlight and, in turn, increasing the warming and melting. Satellite data and surface-based
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A Vision for the International Polar Year 2007–2008 TABLE 3.1 Evidence of recent environmental change in the polar regions Parameter Recent Evidence of Change Surface air temperature Significant temperature increases have occurred on the Arctic and the Antarctic peninsula. Sea ice cover and ice sheet mass balance The Arctic sea ice and snow cover has diminished considerably over the past two decades, particularly in summer, consistent with indigenous observations of early sea ice break-up and later freezes. Winter ice and snow conditions are also less stable. In addition, most glacial ice sheets in both polar regions have thinned, millennia-aged floating ice shelves are disintegrating, iceberg calving in the Antarctic has increased in frequency, and rapid rates of ice sheet thinning have been observed. Ocean circulation Dramatic changes in the circulation of the Arctic Ocean include a) the relocation of the boundary between the Atlantic and Pacific domains from the Lomonosov Ridge to the Alpha Mendeleyev Ridge system, and b) warming of the Atlantic layer and erosion of the cold halocline over the Eurasian Basin. The latter phenomenon exposes the sea ice cover to increased heat from below. Permafrost Permafrost degradation or thawing is occurring in northern Alaska, Canada, Russia, Mongolia, and China. Pollution Episodes of smog-like Arctic haze plague the spring surface layer, and high levels of toxic chemicals (Persistent Organic Pollutants, heavy metals, radionuclides) have been found in the Arctic environment. Fisheries The Bering Sea fisheries have been changing for decades, with a rapid decline in salmon and crab populations observed in the 1990s. There also has been a possible increase in shrimp population near Kodiak Island. Birds and flora Significant modifications to the distribution and migration patterns of many terrestrial and marine animal and plant species have been observed. These data are confirmed and substantially expanded by the observations of local residents, who report major changes in wildlife distributions, earlier spring arrival of many migrating animal and bird species, and the sighting of previously unknown life forms in the polar regions. There also are significant increases in greenness in the Arctic, particularly the expansion of shrubs. Water cycle Research indicates enhanced precipitation over the Antarctic peninsula and increased river runoff in northern Eurasia. Carbon cycle A decrease in sea ice extent will decrease ice algal production with impacts on higher trophic levels. Earlier sea ice melt in the Bering Sea has coincided with declines in carbon flux to sediments, faunal populations, and higher trophic levels. SOURCES: Serreze et al., 2000; IPCC, 1998, 2001. observations indicate that Arctic sea ice areal coverage has declined about 7 percent since 1978 (Johannessen et al., 2004). Change is sometimes dramatic: several times in the past decade, Arctic and Antarctic ice shelves, which are the extension of ice sheets into the ocean, have undergone spectacular breakups (Scambos et al., 2000; Mueller et al., 2003).
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A Vision for the International Polar Year 2007–2008 Even more significant is the predicted complete loss of the multiyear sea ice by the year 2100. The consequences of ice loss range from increased coastal erosion to an altered Arctic heat budget and increased safety risks on native coastal ice hunting grounds. The loss of summer sea ice not only endangers ice-endemic species like polar bears and the food web producing their prey but also will impact the biological cycles of the entire Arctic from the coast to the deep sea (Gradinger, 1995). As the sea ice disappears, understanding its role in the Arctic’s biological cycles is an urgent issue critical to predicting the consequences of changes for the entire Arctic. The climate of the Arctic has undergone rapid and dramatic shifts in the past, and there is no reason it could not experience similar changes again in the future. Records such as ice cores and sediment show climatic cycles that have occurred regularly on timescales from decades to centuries and longer and that are most likely caused by oceanic and atmospheric variability and variations in solar intensity. The Little Ice Age and Medieval Warm Period were examples of long-term cooler and warmer climates, respectively, while shorter-term decadal cycles such as the North Atlantic Oscillation and the Pacific Decadal Oscillation, among others, have been found to affect the Arctic climate. Since the industrial revolution in the nineteenth century, anthropogenic greenhouse gases have added another major climate driver. In the 1940s the Arctic experienced a warm period, like much of the planet, although it did not reach a level as warm as that evident in the late 1990s (Figure 3.2). It is the broadly accepted consensus of the science community that most of the global warming observed in the past 50 years is attributable to human activities (IPCC, 2001), and there is new and strong evidence that in the Arctic much of the observed warming over the same period is also due to human activities (ACIA, 2004). FIGURE 3-2 Records of annual mean surface air temperature for the Northern Hemisphere (blue) and the Arctic (red) from land-station data show that air temperatures above land surfaces in the Arctic appear to have warmed at a faster rate than the whole Northern Hemisphere during the twentieth century. The Arctic record shows a great deal of internal variability. Warming in the early part of the century is exceptionally large in the Arctic, as is the cooling that follows, which could indicate that this phenomenon originated in the Arctic. Alternatively, the enhanced response in the Arctic could be due to its sensitivity to external forcing. SOURCE: Jones and Moberg, 2003.
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A Vision for the International Polar Year 2007–2008 The world’s oceans transport an enormous amount of heat poleward, moderating the global temperature. The polar oceans play a key role in forming the cold dense waters that sink in polar regions and drive ocean heat transport (Johannessen et al., 1994). One hypothesis to explain the suppression of recent change in the Antarctic relative to the Arctic is that ocean circulation changes around Antarctica have greatly increased the uptake of heat from the atmosphere in the Southern Ocean. Global climate models support this hypothesis and also predict that change in the Antarctic will eventually catch up with the Arctic near the end of this century (Manabe and Stouffer, 1994). The polar atmosphere is another interactive link with the rest of the globe. Of the three global-scale fundamental modes of climate variability, two are rooted in the polar regions, the northern hemispheric annular mode and the southern hemispheric annular mode. The polar regions are at the center of hemispheric-scale circulation patterns, which coordinate variability in the environment across continents and ocean basins. These prominent circulation patterns have exhibited trends in recent decades that have a clear imprint on the spatial pattern of changes in air temperature, sea ice, snow cover, and storms, as well as many other components of the environment (e.g., Thompson and Solomon, 2002). The land surface in the high northern latitudes is characterized by expansive snow cover in winter, followed by sharply peaked runoff and intense vegetation growth. Snowfall and rain have increased in many areas in recent decades, and so has discharge from many Arctic rivers (Serreze et al., 2000). An increase in rain in winter creates ice layers that are difficult for caribou and reindeer to paw through and that have been found to reduce their populations. Warmer and moister conditions are known to alter tundra vegetation, which in turn influences carbon uptake in the vast northern lands. Changes in snow cover also affect human activity. Exploration for oil and gas reserves on the North Slope in Alaska are only allowed when snow cover is at a depth adequate to protect the underlying tundra ecosystem, and the window of deep-enough snow cover has been decreasing in recent years (NRC, 2004a). Ecosystems Arctic and Antarctic systems are rich and diverse habitats for life. Key biogeochemical cycling processes occur in this extreme environment, being directly influenced by sea ice and snow cover, seawater hydrography (nutrients, salinity, and temperature), variable light levels, and atmospheric conditions. Polar organisms have adapted over time to live in an extremely cold environment and thus are among the most intimately susceptible of all species to climate warming events. Rising temperatures threaten the structures of their habitats as well as the function of their physiological processes. Arctic sea ice is melting, and associated reductions in the extent of ice cover and ice thickness, and the impacts of these changes on the biological system, are dramatic and potentially devastating to certain species (Krajick, 2001; Whitfield, 2003). If the sea ice summertime coverage continues to decline (Figure 3.3), marine ice algae also would decline due to loss of substrate. The supply of algae has a cascading effect to higher trophic levels in the food web: small planktonic animals (zooplankton) feed on algae; many fish, such as cod, feed on these zooplankton, and sea birds and mammals in turn feed on the fish (Eastman, 1993). Species like polar bears would also be affected by a loss of sea ice as they almost entirely depend on it for foraging, hunting, and migrating.
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A Vision for the International Polar Year 2007–2008 FIGURE 3-3 Reduction in sea ice extent in the Beaufort and Chukchi Seas over a three-year period. The ice cover in 1998 was a then-record-minimum low north of Alaska for the satellite era (post-1979). Since 1998, a new record low was observed in the summer of 2002 (Serreze et al., 2003), and 2003 was a close second (Fetterer et al., 2004). Sea ice concentration estimates derived from passive microwave satellite data. SOURCE: Comiso et al., 2003.
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A Vision for the International Polar Year 2007–2008 Thinning Ice Threatens Polar Bear Habitat and Polar Food Web The primary natural habitat of the polar bear is under increasing threat as a consequence of thinning of the Arctic sea ice, which has decreased between 10 and 40 percent since the 1960s. Polar bears rely on the ice to hunt for seals, and its earlier breakup is giving them less time to hunt. Looking ahead, some climate models predict a total loss of multiyear sea ice in the north by 2100 (USGCRP, 2001). What exactly would this mean for endemic species like the polar bear and the food web that produces their prey? Microscopic Arctic ice algae, for example, contribute as much as 50 percent of the total primary production at the bottom of the food web in high Arctic basins. The loss of the ice would have rippling consequences through the entire ecosystem. SOURCE: Mark Weber, U.S. Fish and Wildlife Service. Another indicator of contemporary Arctic change is the occurrence of an intense phytoplankton (coccolithophorid) bloom that is normally associated with warmer temperate regions. In 1997 such a bloom caused a massive die-off of short-tailed shearwaters, a seabird that annually migrates from nesting grounds in Australia to forage in the Bering Sea of Alaska (Hunt et al., 2002). Coincident with these changes was a buildup and then a crash in the biomass of large jellyfish (Brodeur et al., 2002). Other changes include declines in bottom-dwelling clam populations in the shallow northern Bering and Chukchi shelves in the 1990s, with these prey tightly linked to marine mammals and birds that are consumed by northern residents. Migrating gray whales shifted their feeding areas farther north in the 1990s, coincident with declines in bottom-dwelling shrimp-like amphipods (Moore et al., 2003). Studies in the south-eastern Bering Sea suggest a reduction in overall productivity in the region (Schell,
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A Vision for the International Polar Year 2007–2008 Although primarily a high latitudes phenomenon, the northern lights have been seen as far south as Texas and are regularly seen at latitudes equivalent to New York. While historical references date as far back as centuries before Aristotle, it was not until the twentieth century that these celestial lights were understood. The dancing colors of the aurora reflect a large-scale electrical discharge phenomenon associated with oxygen and nitrogen atoms. SOURCE: Jan Curtis, University of Wyoming. 2000), whereas benthic (deep) population declines in the northern Bering Sea during the 1990s are coincident with reduced transport and a freshening of waters transiting the Bering Strait (Grebmeier and Dunton, 2000). Similarly, some studies have hypothesized and others have shown that fisheries are displaced as they follow the retreating ice edge (SEARCH, 2001; Hunt and Stabeno, 2002). Ultimately, changes in physical forcing and the impacts on biochemical cycling influence the air-sea flux of carbon dioxide as well as the sequestration of carbon to depths at both polar regions. The Southern Ocean plays a central role in the global carbon cycle and biological productivity, and it responds to climate forcing (Sarmiento et al., 1998). Recent ecosystem studies in the Ross Sea, Antarctica, suggest that changes in ice extent and nutrient availability influence phytoplankton species’ growth and the subsequent recycling of carbon in surface waters or deposition and sequestration of carbon to depth (DiTullio et al., 2000; DiTullio and Dunbar, 2003). A warming ocean may be causing the melting of the Larsen Ice Shelf in Antarctica (Kaiser, 2003; Shepherd et al., 2003), and the subsequent freshening of the surface waters is expected to alter carbon cycling in this region. The high rate of warming on the Antarctic Peninsula—the fastest-warming region on Earth—has led to increased precipitation. When precipitation falls as snow, it can
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A Vision for the International Polar Year 2007–2008 reduce the amount of bare ground that is available for penguin rookeries. Penguin populations in some areas appear to be in decline for this reason. The ectothermic (“cold-blooded”) marine species of Antarctic waters, which have evolved under stable “ice bath” conditions for millions of years, may have only limited abilities to acclimate to warmer temperatures. These organisms may be especially threatened by continuing global warming. Forcings To understand the cause of recent changes and to project future change with confidence requires understanding of how anthropogenic forcings, natural forcings, and internal variability each contribute to recent trends. The most important anthropogenic forcings relevant to the climate of the twentieth century were an increase in greenhouse gases, an increase in sulfate aerosols, and a decrease in stratospheric ozone. The natural forcing factors included variations in solar irradiance and volcanic aerosols. Internal dynamics of the climate system alone caused the climate to be unsteady. The polar regions are prone to greater internal variability than anywhere else on Earth, owing to the presence of ice and snow and the formation of dense waters in the polar oceans. Because of the complexity of the climate system, uncertainty remains in the relative contribution of each of these to the twentieth century warming (IPCC, 2001) and to the polar environment. Nonetheless, the IPCC (2001) has stated that most of the global warming observed over the past 50 years is attributable to human activities, and there is new and strong evidence that in the Arctic much of the observed warming over the same period was also due to human activities. Many characteristics of the recent change are consistent with those predicted by global climate models (Gregory et al., 2002). These models predict continued warming this century, especially in the Arctic, due to projected changes in anthropogenic forcing (Figure 3.4). In fact, the polar regions may already be harbingers of impending global change, but we cannot be certain because of limited understanding of the environmen- FIGURE 3-4 Projections of composite mean September Arctic sea ice changes extent based on the IPCC 2001 B2 scenario in five general circulation models: Canadian Climate Centre for Modelling and Analysis, Max-Plank Institute, Geophysical Fluid Dynamics Laboratory, Hadley Centre, and National Center for Atmospheric Research for the Arctic Climate Impact Assessment. SOURCE: ACIA, 2004.
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A Vision for the International Polar Year 2007–2008 The Sun–Earth Environment The Sun is the source of energy for life on Earth and the strongest modulator of our physical environment. The Sun’s influence spreads throughout the solar system, through photons, which provide heat, light, and ionization, and through the continuous outflow of a magnetized, supersonic ionized gas known as the solar wind. Over very long timescales (millennia and more), irregularities in Earth’s orbit affect climate. One great unknown that may affect the environment on century to decadal scales (or less) is variability of the solar output. Little is known about solar variability and the potential role it may play in Earth’s climate. Understanding variations, both long-term and short-term in the Sun’s magnetic activity and radiative output and their couplings to Earth’s space and upper-atmosphere environment, is one of the necessary conditions for distinguishing the human influence on global climate from the background of natural variability. Solar activity, or “space weather,” produces disturbances in the Earth’s space environment that can adversely affect certain important technologies and threaten the health and safety of astronauts. Polar region technologies that can be affected include high-frequency communications, global positioning determinations, power systems, and pipelines. Knowledge obtained through solar and space physics research is essential to the development of means and strategies for mitigating the harmful effects of such disturbances. Geomagnetic field lines thread through the space around Earth and physically link the northern and southern polar regions (see Figure 3.5). These polar region field lines pass close to, and indeed often form, the boundary of Earth’s space environment—the magnetosphere—with the expanding solar atmosphere (the solar wind in the interplanetary medium). Variations and changes in the solar wind are thus experienced first in the polar regions and are often most visibly apparent through production of the northern and southern lights (the aurora borealis and australis) in the upper atmospheres (90 to several hundred kilometers above the Earth’s surface) of the polar regions. Disturbances by the expanding solar atmosphere can often be felt throughout Earth’s space environment. Major challenges in understanding the Sun and the heliosphere include (1) understanding the structure and dynamics of the Sun’s interior, the generation of solar magnetic fields, the origin of the solar cycle, the causes of solar activity, and the structure and dynamics of the solar corona, and (2) understanding the interactions of the expanding solar atmosphere with Earth’s magnetosphere. tal system and the inaccuracy of models. A systemwide assessment of the polar regions and an expansion of monitoring networks are necessary to improve our understanding of the character, mechanisms, and impacts of change and to improve our ability to predict future change. LESSONS FROM PAST CHANGE Past change can provide a context for evaluating modern observations of change. For example, proxies of surface temperature, such as from tree rings, pollen, sediments, and ice cores, indicate that the surface warming of the twentieth century averaged over the Northern Hemisphere (of about 0.6°C over land and ocean) is likely to have been the largest of any century during the past 1,000 years (IPCC, 2001). A similar analysis
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A Vision for the International Polar Year 2007–2008 FIGURE 3-5 Artist’s conception of Earth’s magnetosphere, the volume of space around Earth dominated by the geomagnetic field and populated with plasmas of both ionospheric and solar wind origin. The ionized gases that populate the magnetosphere are remarkably dilute: the densest magnetospheric plasma is 10 million times less dense than the best laboratory vacuum. Nevertheless, the motions of these highly tenuous plasmas drive powerful electrical currents, and during disturbed periods, the Earth’s magnetosphere can dissipate well in excess of 100 billion watts of power—a power output comparable to that of all the electric power plants operating in the United States. of proxy data from high northern latitudes in combination with climate modeling has shown that the warming during the twentieth century was most likely a result of increased levels of greenhouse gases, as opposed to solar variability and volcanic aerosols (Overpeck et al., 1997). Large-Scale Environmental Change The environment has undergone rapid and dramatic shifts in the past, and there is no reason it could not experience similar changes again in the future (NRC, 2002). Figure 3.6 shows temperature and snow accumulation since the tail end of the last ice age from a Greenland ice core, including the large change in temperature in the transition from the last ice age toward modern values. Most of the change since the last
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A Vision for the International Polar Year 2007–2008 FIGURE 3-6 Climate changes in central Greenland over the last 17,000 years. Reconstructions of temperature and snow accumulation rate show a large and rapid shift out of the ice age about 15,000 years ago, an irregular cooling into the Younger Dryas event, and the abrupt shift toward modern values (Cuffey and Clow, 1997; Grootes and Stuiver, 1997). The 100-year averages shown somewhat obscure the rapidity of the shifts. Most of the warming from the Younger Dryas required about 10 years, with 3 years for the accumulation-rate increase. A short-lived cooling of about 6°C occurred about 8,200 years ago. Climate changes synchronous with those in Greenland affected much of the world. SOURCE: NRC, 2002. peak of the ice age, about 12,000 years ago, in a period known as the Younger Dryas, occurred within a span of a few decades. Yet much smaller changes of only a degree or two, which are known to have occurred in between the so-called Medieval Warm Period and the Little Ice Age, were sufficient to cause Scandinavian settlers to colonize Greenland during the warm periods and then to abandon those farms during the cold. Many past examples of societal collapse involved rapid change to some degree (NRC, 2002). Natural records preserved in sediments, caves, and ice cores show that the climate system has crossed thresholds that resulted in abrupt changes, where a small change in one part of the system resulted in a sudden and large response in another (NRC, 2002). For instance, ice core records indicate that Greenland warmed by about 10°C in as little as a decade more than a dozen times during the last glacial cycle (Severinghaus et al., 1998; Alley et al., 1993). These abrupt warmings were followed by a slow cooling over roughly 500 years (Figure 3.6), with about 1,500 years between abrupt changes (Rahmstorf, 2003). These timescales suggest that the ocean and/or continental ice sheets might be key players. Although the precise nature of the threshold mechanism is
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A Vision for the International Polar Year 2007–2008 unknown, these players are active in our climate system today. If Earth continues to warm beyond natural rates, abrupt change could be in our future. Paleobiology Just as the chemistry of polar ice reveals much about the environments of the past, the layered chemical and biological histories preserved in the ice also preserve evidence of past ecosystems. Ice coring studies have shown that in some cases metabolically active microbes may exist in small liquid water veins in solid glacial ice (Price, 2000), or organisms may be cryopreserved and metabolically inactive within the ice; viable microbes thousands of years old have been found in ice cores (Doran et al., 2003). Genomic methods provide a tool for characterizing the identity of organisms and organism remains and may enable new links between climate and biological adaptation, as well as insights into conditions for life on other planets. From October 1997 until October 1998, scientists based on a ship frozen into the Arctic ice near the North Pole conducted experiments to better understand changes in the ice, ocean, and atmosphere. The project, known as SHEBA (Surface Heat Budget of the Arctic), was supported by the National Science Foundation. As part of the SHEBA ice station project, Jackie Richter-Menge and Bonnie Light read ice thickness gauges as the ice melted in August 1998. SOURCE: SHEBA Project Office. SOURCE: SHEBA Project Office.
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A Vision for the International Polar Year 2007–2008 Forcings Paleo evidence from the last few ice ages provides a rich picture of the climate variability on multidecadal to millennial timescales, which is fundamentally driven by internal dynamics of the environment subject to variability in the total solar irradiance and volcanic aerosols. It shows how the climate is capable of behaving in the absence of anthropogenic forcing. We must look on longer timescales to understand how climate can respond to more substantial natural forcings. Paleo data indicate that feedbacks in the polar regions have been responsible for enormous environmental change owing to alterations in the Earth’s atmospheric composition and incoming solar distribution, the buildup of ice sheets, and continental drift (Crowley and North, 1996). Figure 3.7 shows FIGURE 3-7 Variation in Earth’s temperature during the past 80 million years, based on reconstructions from deep-marine oxygen isotope records. SOURCE: Barrett (2003).
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A Vision for the International Polar Year 2007–2008 the history of global temperatures for the past 80 million years. Major puzzles remain regarding why glaciations were intermittent and what caused major warmings and coolings on top of the very long global cooling of the past. While exciting discoveries have prompted a great deal of recent theoretical advancement, the fundamental mechanisms driving variability on a variety of timescales are still not well understood. Expanding data-gathering efforts to provide new proxy records on past climates would help improve our understanding of recent discoveries. Added spatial coverage would allow us to identify modes of climatic variability, which may shed light on the basic physics driving these modes and their relevance to the modern environment and societies. Unraveling the Secrets within Polar Ice When Richard Alley thinks about working at the poles, he thinks about sitting in the midst of endless snow, in the middle of Greenland, 200 miles from anywhere, and having an Arctic fox trot into camp. He thinks of white snow and blue snow, white clouds and blue skies. He thinks of black rocks along the coast and red coats on people; of musk, seals, and penguins, and snow crunching underfoot. He thinks of the aurora. “The aurora is wonderful. It is the bioluminescence of a blooming sea spread above rather than below.” As a professor of Geosciences at The Pennsylvania State University, Alley has been on six expeditions to Greenland and three to Antarctica, and he’s worked in Alaska as well. Primarily, he investigates the role of glaciers and ice sheets in the climate system, including the flow of ice and possible effect on sea-level change, and records of climate change preserved in ice cores. He does this, he says, “because, it’s interesting, it’s fun, and it will help people.” In the 1990s, Alley and his colleagues participated in drilling two miles into Earth’s ice in Greenland. There they found atmospheric chemicals and dust that enabled them to glimpse such phenomena as wind patterns and precipitation for the past 110,000 years. The cores revealed a sweeping story of climatic history as clear as that found by reading any book. “The cores tell us of the great ice-age roller coaster that cooled the Earth over tens of thousands of years and grew ice across almost one-third of the land—and then melted most of that ice away,” he explains. “More surprisingly, although the warming from the ice age took 10,000 years, about half of the warming in Greenland happened within about 10 years. At the same time, very large and rapid climate changes affected much of the Earth. Similar abrupt climate changes happened repeatedly through the ice age and even into the warmth of the last 10,000 years—almost like a climatic bungee-jumper on the ice-age roller coaster.” Currently, Alley is part of a team finishing up a study of an ice core from West Antarctica. They are planning for a second, deeper core there. The Antarctic projects are intended to find the southern hemisphere equivalent of the Greenland coring. By comparing climatic history in the northern and southern hemispheres, scientists will be able to better understand what happened in the past, which should help in predicting global trends in the years ahead. Richard Alley on the Matanuska Glacier in Alaska. SOURCE: Todd Johnston.
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A Vision for the International Polar Year 2007–2008 Alley’s findings from the Greenland ice cores were published in The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change, and Our Future, in 2000. The book shows how wiggles in Earth’s orbit, changes in ocean currents, volcanic eruptions, variations in greenhouse gases from humans and nature, and more, have combined to provide the fascinating climatic history of Earth. It also suggests how humans are becoming more and more important in controlling the future of the climate, and how abrupt climate changes might affect our choices about what to do in the future. Humans are changing the atmosphere in many ways, according to Alley. “Our leaded gasoline dirtied the snow of Greenland until we decided to get the lead out. Cleaner snow now shows our success. But air bubbles in the ice reveal that CO2 and other greenhouse gases, mostly from our activities, are building up to levels not seen for a very long time. Historians and physicists agree that this will warm the planet.” According to Alley, mountain glaciers already are melting as the world warms, and their water is swelling the oceans. Too much warming could melt the great ice sheets in Greenland and Antarctica, with much more impact on the coasts. If Greenland were to melt, sea level would rise a bit more than 20 feet, which without sea walls, would put Miami, Florida, mostly under water. If all the ice sheets were to melt, sea level would rise 200 feet or slightly more, which would put Florida under water and the coast up in Georgia. Melting ice puts fresh water into the nearby oceans, which might change the way the oceans circulate. If this occurs, it will not cause a new ice age, an end to civilization, or a really dramatic disaster movie—but it could cause cooling in some regions, warming in others, and shifts in rainfall and droughts, with large enough impacts to matter to many people. “We know that days are usually warmer than nights, summers usually warmer than winters, but we still check the weather forecast, because more information really is useful,” says Alley. “Similarly, decades with high carbon dioxide usually are warmer than those with much lower carbon dioxide, but we have a lot of work to do to make climate forecasts as useful to humanity as weather forecasts are now. Our studies of ice are part of that important work. I can’t wait to get back to work!”
Representative terms from entire chapter: