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CLIMATE CHANGE AND MARINE AND TERRESTRIAL SYSTEMS

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    ... CAPITOL HILL HEARING TESTIMONY 8939 words SENATE COMMERCE, SCIENCE AND TRANSPORTATION GLOBAL CLIMATE CHANGE AND IMPACTS CLIMATE CHANGE AND MARINE AND
    Message 1 of 1 , Apr 29, 2006
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      CAPITOL HILL HEARING TESTIMONY

      8939 words

      SENATE COMMERCE, SCIENCE AND TRANSPORTATION

      GLOBAL CLIMATE CHANGE AND IMPACTS


      CLIMATE CHANGE AND MARINE AND TERRESTRIAL SYSTEMS

      ROBERT CORELL, SENIOR POLICY FELLOW

      AMERICAN METEOROLOGICAL SOCIETY

      Statement of Robert Corell Senior Policy Fellow, American
      Meteorological Society

      Committee on Senate Commerce, Science and Transportation Subcommittee
      on Global Climate Change and Impacts

      April 26, 2006

      Introduction

      Mr. Chairman, Members of the Sub-Committee, and all gathered here
      today, I thank you for the opportunity to participate in today's
      hearing on the "Projected and Past Effects of Climate Change: A Focus
      on Marine and Terrestrial." I am honored to join you to explain the
      science that underpins understanding of the past and projected
      effects of climate change, especially in terms of the impacts on
      marine and terrestrial systems in North America, across the Arctic
      region, and around the world.

      In offering these perspectives, I will be drawing primarily from the
      findings of major scientific assessments, a number of which I have
      been involved with, because these assessments very thoughtfully draw
      together the collective findings of the scientific community. These
      assessments deserve very high and special consideration because their
      credibility has been well established as a result of their extensive
      open review processes, which have helped to carefully hone their
      findings.

      At the national level, I will be drawing upon the results of the US
      National Assessment that was completed five years ago.In my role from
      1990-99 as chair of the Subcommittee on Global Change Research that
      directed the US Global Change Research Program, I was instrumental in
      the organization of this assessment, and after I left government
      service I served on the National Assessment Synthesis Team that
      summarized the assessment's findings. In describing potential
      consequences for the Arctic, I will be drawing mainly from the
      results of the Arctic Climate Impact Assessment (ACIA), which was
      completed in 2004,having been established and charged to conduct the
      assessment by the Arctic Counciland the International Arctic Sciences
      Committee.For ACIA, I served as chair, leading an international team
      of over 300 scientists, other experts, and elders and other
      insightful indigenous residents of the Arctic region in preparing a
      comprehensive analysis of the impacts and consequences of climate
      variability and changes across the Arctic region. At the
      international level, I will be drawing mainly from the results of the
      Intergovernmental Panel on Climate Change (IPCC), which I was
      instrumental in helping to conceive in the late 1980s in my role as
      Assistant Director for Geosciences at the National Science Foundation
      (NSF) from 1987-1999. The IPCC's members are the nations of the world
      and the periodic assessments that they commission represent the
      collective evaluation of scientific understanding by the
      international scientific community. That the IPCC's assessments of
      1990, 1995, and 2001 have been unanimously accepted by the world's
      community of nations gives a strong indication of the widespread
      agreement that exists regarding the major finding that human-induced
      climate change is already influencing the climate and the environment
      and that much larger changes lie ahead.For more detailed information
      and scientific citations on most of my points, reference should be
      made to the cited assessments. In areas where the pace of research
      has been especially rapid or significant in recent years, however, I
      will also be drawing upon the results of more recent scientific
      articles, which I will specifically reference.

      Context for Today's Hearing

      The IPCC's Third Assessment Reportsummarized the peer-reviewed
      scientific evidence that human activities, in particular the ongoing
      emissions of carbon dioxide (CO) and other greenhouse gases to the
      atmosphere resulting primarily from the combustion of coal, oil, and
      natural gas, are causing the Earth's climate to warm more rapidly and
      persistently than at any time since the beginning of civilization.
      While some of the fluctuations are likely a result of natural factors
      (e.g., variations in solar irradiance and major volcanic eruptions),
      the IPCC evaluation concluded that the strength and patterns of these
      change makes clear that human influences are responsible for most of
      the roughly 0.6C (1F) warming during the 20century.

      In particular, despite the cooling influence of the 20century's
      largest volcanic eruption in 1991, the fifteen warmest years in the
      instrumental temperature record available since 1860 have all
      occurred in the last 25 years,and comparison with paleoclimatic
      reconstructionsof temperatures over the last two thousand years
      indicates that recent warmth is unprecedented, at least for the
      Northern Hemisphere where paleoclimatic data are most available.In
      addition to the warming of the surface, which has been particularly
      strong in the Arctic,warming is also evident in ocean temperatures
      (causing some of the sea level rise), below ground temperatures, and
      temperatures well up in the troposphere.Other evidence of climate
      change includes diminishing sea ice and snow cover in the Northern
      Hemisphere, melting back of mountain glaciers in the tropics and in
      most other locations around the world, and an increasing tendency for
      precipitation to occur in relatively heavy amounts.

      For the future, IPCC projects that significantly greater warming lies
      ahead. Considering a wide range of possible scenarios for how human
      activities (e.g., changes in population, technological development,
      energy use and supply, economic development, and international
      cooperation) are likely to alter atmospheric composition during the
      21century, the IPCC projects a further increase in average annual
      surface air temperature around the globe of roughly 1-2C (1.8-3.6F)
      from 1990 to 2050 and a further 1-2.5C (1.8-4.5F) by 2100, bringing
      the projection for total human influence from the start of the
      Industrial Revolution to 2100 to roughly 2.5-5C (about 4.5-9F).As is
      the case for the warming over the 20century, future changes are
      expected to be greater over land than over the ocean, greater in mid-
      to high latitudes than in low latitudes, and, except where regions
      really dry out, greater during the winter than during the summer and
      greater during nighttime than daytime. As will be explained more
      fully in discussing likely impacts, many other aspects of the world's
      weather and climate will also be affected.

      That such changes in the climate will occur as a result of human
      activities is no longer scientifically controversial. During the rest
      of my testimony, I will discuss what the likely consequences of the
      changes in atmospheric composition and climate are likely to be for
      the environment, focusing on three specific domains:

      -- Oceans and marine systems;

      -- The terrestrial biosphere; and

      -- The interface between the marine and terrestrial environments.

      My discussion will focus on the links between climate change and
      these systems. It is important to recognize, however, that a number
      of additional stresses are affecting each of these environments,
      including air pollution, nitrogen deposition, toxics such as mercury,
      unsustainable extraction of resources, over-fishing, nutrient-induced
      eutrophication, depletion of stratospheric ozone and UV enhancement,
      etc. Climate change is thus only one aspect of global environmental
      change, although a continuously accumulating one that over time will
      have very large impacts, and for a full evaluation of likely
      environmental consequences for both marine and terrestrial
      environments, comprehensive research and assessment efforts are
      essential.

      Interactions and Impacts Linking Climate Change and the Ocean and
      Marine Environment

      Oceans cover about 70% of the Earth's surface. Because of their large
      heat capacity, the oceans moderate climatic swings by supplying heat
      to the atmosphere and adjacent continents during the winter and,
      because they warm relatively slowly during the summer, are the source
      of cooling sea breezes during times of peak solar radiation. Much of
      the heat absorbed by the oceans goes into evaporating water,
      providing the moisture that supplies vital precipitation for land
      areas via the monsoons and tropical and extratropical storms. These
      rains and associated geochemical interactions help to cleanse the
      atmosphere of pollution. In addition, oceans support a wide diversity
      of biological life that supplies fish, birds, marine mammals and
      other species higher in the food chain, and supports the fisheries
      that in turn provide substantial food for humans.

      While the oceans seem so large that it is hard to imagine that human
      activities could affect them, records over geological time and
      observations of recent changes make clear that both the physical and
      biological systems in the ocean are quite sensitive to changes, and,
      indeed, are being affected. The very human activities that are
      causing the climate to change are becoming the major influence on the
      oceans.

      First, the oceans affect atmospheric chemistry. In their natural
      state, cold waters forced to the surface by wind patterns in low
      latitudes release large amounts of COto the atmosphere as they warm.
      Before humans started altering the carbon cycle, roughly the same
      amount was taken up in mid- to high latitude ocean areas as the ocean
      waters cooled and marine organisms grew, died and sank to the ocean
      depths. With this balance, which was modified somewhat during glacial
      periods when the oceans were colder, the atmospheric COconcentration
      has been held in the range of about 180 to 300 ppmvfor the past
      several million years. As human activities began to emit large
      amounts of COas a result of combustion of coal, oil, and natural gas,
      the atmospheric concentration has been driven higher because the
      oceans and living biosphere cannot absorb it all. On time scales of
      years to centuries, the oceans take up about a third of the emitted
      amount, limiting the atmospheric buildup and thus moderating the pace
      of climate change.

      While the oceans as a whole can hold vast amounts of dissolved CO,
      the oceans are not well mixed vertically, and so most of the added
      CObuilds up in the near surface layer. This has the effect of
      altering oceanic chemistry, most importantly by making the ocean more
      acidic.

      Increasing oceanic acidity has a range of effects, but most important
      makes it chemically more difficult for marine organisms to form
      shells. For corals, the rise in the COconcentration from its
      preindustrial value of about 280 ppmv to its present value of 380
      ppmv has already caused a significant shrinkage in the regions most
      favorable for reef-forming, and by 2050, virtually all of the most
      favorable regions in the world will have disappeared, simply due to
      the rise in the COconcentration.Adding in the sensitivity of corals
      to warmer ocean waters (the "coral bleaching" effect), the prospect
      for more powerful storms and wave conditions, the increasing threats
      from coastal runoff and fish-harvesting, and other stresses, the
      prospects for many of the world's reefs are very problematic. While
      the potential impacts on coral are of most immediate concern, impacts
      on other shell-forming organisms are also likely to become
      significant over coming decades, particularly as the COlevel
      approaches 750 ppmv.As the rising concentrations of COand other
      greenhouse gases have trapped more infrared radiation, making it more
      difficult for the Earth's surface to cool, most of the additional
      heat has been taken up by the oceans because they are capable of
      mixing it through the upper hundred meters (yards) or so of ocean
      depth. Surveys of ocean temperature give a clear indication that the
      ocean's upper layers are warming;indeed, the warming that is being
      observed is in good agreement with climate model simulations of how
      the oceans are being projected to warm as a results of the changes in
      atmospheric composition.

      This oceanic heating is having a wide range of both physical and
      biologically important impacts. Because the oceans are able to mix
      the heat downward, they are able to slow the warming of the
      atmosphere, which is beneficial, but it also means that we are not
      experiencing the full extent of warming to which past emissions of
      COhave committed the world. Experiments with climate models indicate,
      for example, that the world would be committed to further warming of
      about 0.5C (almost 1F) even if global emissions of COwere to be
      quickly cut to near zero.

      Warming of the oceans also makes more energy available to the
      atmosphere if just the right conditions prevail. For example, warm
      ocean waters provide the energy needed to intensify tropical cyclones
      (i.e., hurricanes and typhoons), and indeed, recent studiesare
      finding that increasing sea surface temperatures are leading to an
      increasing proportion of tropical cyclones to be in the most powerful
      and destructive categories (more on the consequences of more powerful
      tropical cyclones in the section dealing with the ocean-land
      interface). While there has been significant debate recently about
      whether the available record provides a definitive indication of this
      linkage, a paper in press in the Bulletin of the American
      Meteorological Society, of which I am a co-author, finds that there
      are many reasons to suggest that there is indeed a strong linkage and
      that it may well be limitations in our detective work that are the
      problem.If this is indeed the case, and it seems quite likely, then
      the world faces a situation where the storm season is becoming
      longer, storms may well last longer, and the likelihood of relatively
      intense storms is increasing, likely leading to greater and greater
      destruction and loss of life unless our adaptive effortsare
      significantly increased.

      Climate change also has the potential to influence the pattern and
      character of the normal yearto- year fluctuations of the climate. For
      the Pacific region and then for much of the US, the natural variation
      of the El Nino-Southern Oscillation (ENSO) is of critical importance,
      variously causing El Nino and La Nina events (i.e., unusual warming
      or cooling in the eastern tropical Pacific, respectively) that
      redirect the Northern Hemisphere jet stream, thereby creating either
      quite wet or quite dry winter conditions across various parts of the
      US (e.g., this year, the ocean conditions are causing the US West
      Coast to be inundated with very large amounts of rain).

      Research to date only hints at how ENSO may be affected, with some
      indication that the overall conditions may become more El Nino-like
      with more intense El Nino events (meaning, for example, more winter
      precipitation for California, increasing flooding potential in the
      spring and increasing the stock of burnable vegetation). However,
      there remains significant disagreement among model results and this
      area is, therefore, being investigated intensively by various
      research groups.

      Changes in atmospheric winds and weather (a result of the warming)
      and increasing ocean temperatures (which also feed back to affect the
      weather) also lead to changes in ocean currents.

      Under normal conditions, warm ocean waters are pulled poleward to
      replace cold waters that sink to the ocean depths in high latitudes.
      As these waters are pulled poleward, for example in the Gulf Stream,
      heat is given off that tends to keep Europe relatively warm in
      winter, given its latitude. As climate change prevents ocean waters
      in high latitudes from cooling as much, the rate of sinking waters
      declines, and so less warm water is pulled poleward, providing less
      winter heat. While this slows the human- induced warming rate in
      Europe, it leaves that heat in lower latitudes, causing those regions
      to be warmer and even more moisture to evaporate, moisture that is
      likely to result in more intense rainfall events. Slowing the
      generation of oceanic deep water also slows the transport of
      dissolved COinto the deep ocean, releasing somewhat the oceanic brake
      on the pace of global warming.

      Fisheries, marine mammals, seabirds, and other marine life will all
      be significantly affected by these changes. Both the increasing
      temperature and freshening of upper ocean waters in some regions by
      increased precipitation will tend to increase stratification of the
      upper ocean, affecting the vertical distribution and productivity of
      biological activity.Shifts in fisheries will occur (and some changes
      are already being observed) as ocean temperatures shift and changes
      in abundance will occur as the amounts of upwelling nutrients and
      associated biological activity are reduced. The retreat of sea ice
      will also lead to changes in fisheries, as the ice edge is normally a
      very productive site as a result of the release of nutrients from the
      melting ice and the protection from intense waves provided by the ice
      itself. Marine mammals, including walrus, seals, and polar bears,
      depend on the presence of sea ice to raise their young and to hunt
      for food, and the retreat of ice is already having a significant
      impact.The shifts in ocean conditions, both of sea ice and of
      biological activity, are also starting to have effects on sea birds,
      which are also facing increasing competitive pressures from birds
      that normally are shifting northward as warming increases.

      An added result of sea ice retreat will be the potential for greater
      access by ships. The melting back of sea ice is already near to
      opening the Northern Sea Route that would connect the Atlantic and
      Pacific Oceans via open water north of Eurasia. Not only would such a
      route cut shipping time significantly, but the route will also
      increase seasonal access to arctic resources, both below coastal
      waters and on land (although, perversely, the summer melting of the
      permafrost will make transport over land much more difficult).
      Already the Northwest Passage is becoming navigable for icebreakers
      and in the decades ahead greater access should be possible.

      Environmentally, such access will greatly increase the risk of
      contamination from spills and other pollution, and there is virtually
      no experience or effective approach for cleaning up such spills.
      Politically, the increased access is already raising questions of
      sovereignty, ownership of coastal zone resources, and rights to the
      shifting fisheries that will result. The identification of such
      issues as part of the Arctic Climate Impact Assessment formed the
      basis of the policy guidance document that was prepared by the Arctic
      nations as a framework for future discussions.Overall, human-induced
      climate change is thus already having significant effects on the
      ocean, the weather systems that the ocean generates, and on the
      biological systems that are dependent on its resources. Adding on the
      impacts of sea level rise on the coastal environment, which is
      treated below, the global oceanic environment on which we all depend
      is already screaming, at least in a figurative sense, for actions to
      greatly slow the pace of change, especially as roughly an equal
      amount of change as has already occurred is almost certain to result
      as a consequence of past human activities.

      Interactions and Impacts Linking Climate Change and the Terrestrial
      Environment

      Changes in both the COconcentration itself and in the climate will
      affect terrestrial systems.

      Because COis needed by plants to grow, the increase in its
      concentration will, as a whole, enhance plant growth and allow the
      stomata (pore openings) on the undersides of leaves to open less,
      allowing less harmful air pollution in and less moisture out, thereby
      improving the overall health and water use efficiency of plants. As a
      general result, the higher COconcentration will thus lead to greater
      carbon uptake and enhanced storage as plant material and in soils as
      long as nutrients and sufficient soil moisture are available. Recent
      studies suggest that the COfertilization effect will be limited by
      tropospheric ozone concentrationsas well as the availability of
      nitrogen in ecosystems.

      However, different plants respond quite differently. Under conditions
      with adequate moisture and nutrients, many types of crops (key
      exceptions are maize, millet, sorghum, and sugar cane) respond quite
      strongly to the increase in the COconcentration, but then so too do
      many weedy plants, necessitating additional control measures.
      Assuming that farmers can overcome problems with weeds and increased
      occurrence of pests and that moisture amounts are sufficient, the per
      acre yield of many food crops is likely to increase by tens of
      percent.It is for this reason that the IPCC and other assessments
      suggest that overall global food production will increase, at least
      until the COconcentration gets much higher when the effect can
      saturate or even changeover (i.e., become essentially toxic). Simple
      economic analysis would then suggest that with more agricultural
      production, food prices will drop and that there will be sufficient
      food, at least for those who can afford it, providing a net economic
      benefit to society. However, the situation in the real world is a
      good bit more complex. In the US, for example, overproduction
      currently leads to the need for subsidies as a result of
      overproduction, and so an increase in productivity and a decrease in
      commodity prices may well lead to calls for larger subsidies. With
      the climate also changing, there will also be a constant need to
      adjust seed strains to ensure optimal productivity,creating greater
      needs for support of crop development programs at, for example, the
      land grant universities.

      In addition, while productivity will go up in both good and marginal
      farming areas, the increase will be greater in absolute amount in the
      better farming areas, and so the economics of farming in marginal
      areas is likely to worsen, leading potentially to the abandonment of
      farming in such areas unless a switch can be made to other crops for
      which there is demand (e.g., a non-food crop that can be used to
      produce biofuels). For those now growing niche crops (e.g., crops
      such as apples and broccoli in cool summer regions such as upstate
      New York and New England; tomatoes in regions where nighttime
      temperatures are cool enough for fruit to set; etc.), warming is
      likely to make such regions uncompetitive for continued production of
      these crops. Because soils are typically not fertile enough to
      compete economically with regions now growing warm season crops,
      farming in such regions is also likely to be threatened. Thus, while
      overall food production in regions such as the US is projected to
      increase, there are likely to be hard times for many farmers (and the
      rural communities are associated with them) as adjustments occur.
      Lost in the transformation is likely to be the effective role present-
      day farmers play in caring for the land, which is likely to create
      ecological challenges because returning such regions as the southern
      Great Plains to their pre-farming vegetation is unlikely to be
      successful due to the altered climatic conditions.

      For natural systems such as forests and grasslands, the situation is
      more problematic. Each ecosystem type has a set of preferred
      conditions, as is evident from the changing distributions of types of
      forest ecosystems going poleward or up a mountain. As climatic
      conditions shift, the preferred ranges for each type of ecosystem
      will shift, and numerical models that simulate this process indicate
      that the projected changes in climate over the 21century will have
      profound effects. Starting from the Arctic (and focusing on the
      coarsest subdivision of ecosystem types), the tundra, which is summer
      home and nesting ground for many migrating birds and mammals, will be
      squeezed against the Arctic Ocean as the boreal forest becomes
      established further and further to the north. Across the United
      States and Canada, temperate forests and grasslands will push
      northward, with the northeast mixed forest giving way to more
      temperate vegetation and with forests giving way to savanna and
      grasslands in regions where precipitation does not increase enough to
      supply the needed moisture in the face of rising temperatures. For
      the southeastern and southwestern US, this balance will be
      particularly important. As described in the US National Assessment,
      if the summertime conditions become warmer and moister, the
      southeastern mixed forest can persist, but if precipitation does not
      increase sufficiently, the soils will dry and the temperatures will
      increase even more, creating a situation where more frequent fires
      become likely to accelerate the transition to a sparser savanna
      woodland situation. In the southwestern United States, increased
      precipitation, particularly in the winter, may be sufficient to
      increase biological productivity in desert areas, allowing greater
      vegetation growth in winter.

      While seemingly beneficial, if summers become hotter and remain dry,
      the potential for increased fire is significant (e.g., increased
      wintertime growth of chaparral would likely only increase the
      likelihood of periodic fires, which can be particularly threatening
      to communities in the West).While adapting to a situation of
      relatively slowly shifting ecosystems on the continental scale may
      seem comparable to adapting to the reforestation of the Northeast
      over the 20century, the actual situation on the local scale, both for
      wildlife and for communities, is likely to be much more challenging.
      This is the case because there are significant variations in the
      response of the different plant species that make up the ecosystems
      to the changes in COand climate, and this will mean that the
      preferred ranges of different species will shift by different amounts
      and at different rates, thus pulling apart current ecosystems without
      there becoming stable climatic conditions in which new ecosystems can
      evolve--instead, everything will be changing at once.

      Determining the thresholds that might lead to abrupt changes in the
      functioning of natural systems is, however, particularly difficult,
      and there are likely to be thresholds or tipping points that initiate
      a sequence of changes beyond which systems are likely to collapse.
      For example, a temperature increase of about 1C per decade since 1970
      in the Kenai Peninsula in Alaska has caused permafrost melting and
      allowed the over-wintering of spruce bark beetles and the influx of
      additional disease vectors, weakening the trees, and enhancing the
      extent and intensity of wildfire. Together, these effects have led to
      the sudden and widespread loss of the white spruce forest, and to a
      situation in which, even were the new climatic conditions stable, it
      would take centuries for new species to develop into a new, fully
      mature ecosystem; with stable conditions not likely for at least many
      decades, development of a new, mature forest system is likely far off
      in the future. As another example of the sensitivity of extant
      ecosystems, a massive die-off of pinyon pine (Pinus edulis) covering
      12,000 square kilometers in the southwestern United States was
      observed during the recent severe drought. Although the soil moisture
      deficit was no worse than the one endured in the 1950s, the higher
      average temperature appears to have combined with the extreme dryness
      to make the trees more vulnerable to attacks from bark
      beetles.Increased frequency of droughts, wildfires, floods, and other
      extremes, including greater damage from increased and more persistent
      winds and precipitation from tropical cyclones, are other types of
      changes that have the potential to exceed the adaptive capacity of
      existing ecosystems.

      In addition, more frequent fires and the reduced productivity of some
      ecosystems will limit the amount of carbon being taken up and stored
      by the biosphere, thus leaving a larger fraction of the emitted COto
      exacerbate global warming. For example, the recent Indonesian fires
      driven by ENSO drying and human land use changes led to significant
      releases of COto the atmosphere.

      A recent international comparison of coupled carbon climate
      simulationsfound that all of the models projected some
      destabilization of tropical ecosystems, leading to soil drying,
      reduced plant/tree growth, and increased occurrence of fire and net
      emission of COto the atmosphere, thereby accelerating warming
      (positive feedback loop).Models typically suggested that by 2100
      these "carbon-climate" feedbacks would lead to the atmospheric
      COconcentration being higher by 20 to 200 ppmvand additional warming
      of 0.1 to 1.5C, with the worst-case model scenario projecting the
      complete die off of the Amazon rain forest. These feedbacks are not
      yet well understood or represented, requiring coupled treatment of
      climate change, COfertilization, nitrogen limitation, and the ability
      of trees to tap deep soil horizon water; however, these processes do
      indicate the potential for the likely outcome being more toward the
      upper end of the IPCC range of possibilities.

      Because projected shifts in the frequency, timing, intensity, and
      location of precipitation will lead to all sorts of challenges,
      issues relating to freshwater resources, although of a variety of
      types, were a common thread across all regions in the US National
      Assessment (see Table 1 for a brief summary of key regional
      consequences). For example, the increased likelihood of additional
      wintertime precipitation in the western US, as projected in both
      models used in the US National Assessment, increases the potential
      for mudslides and high river levels as well as increasing the
      likelihood of mountain precipitation falling as rain, causing
      accelerated loss of the snowpack, a further increase in runoff and an
      even greater likelihood of flooding. At the same time, warmer
      temperatures will lead to a rise in the snowline and, on average, a
      reduction in the springtime snowpack that is so vital for sustaining
      stream and river flows into the summer. For the rest of the US,
      projections indicate a continuation of the shift of precipitation
      toward more precipitation falling in the more intense (i.e.,
      convective) rainfall events. Reducing the time for rainfall to seep
      into aquifers has the effect of increasing runoff, especially once
      the upper layer of soil has become saturated, thereby increasing the
      likelihood of high river levels and flooding.

      Warmer summertime temperatures, and a greater interval between
      significant rainfall events, are projected by many of the models to
      lead to increased evaporation of soil moisture in the Great Plains,
      and so a more rapid onset of drought conditions. For the Great Lakes,
      most models project a few foot lowering of lake levels as the
      increase in summertime evaporation exceeds the increase in winter
      precipitation, significantly impacting community, recreational and
      commercial use of lake waters.Reduced duration and extent of snowfall
      will also affect the Northeast and other areas, likely shortening the
      ski season and lengthening the time for warm weather recreational use
      of the landscape, assuming drying and fire do not become threats.

      In the Arctic, the melting back of snow cover, river ice, and
      permafrost, combined with offshore melting back of sea ice, will have
      significant effects on wildlife and on movement generally across the
      region. For many types of wildlife, the snow cover provides
      protection and even habitat, and climate change is likely to break
      vital links (e.g., lemmings and voles survive the winter mostly
      between the snow layer and the underlying tundra, and their loss
      would deplete food resources for snowy owls and foxes, etc.).
      Reindeer and caribou depend on the snow cover to protect vegetation
      that serves as winter feed, and episodic freeze-thaw conditions can
      create ice crusts that cannot be easily broken, reducing access to
      the food necessary to survive. The migrating herds also depend on
      frozen river ice in springtime to cross rivers along migration routes
      to summer breeding grounds.Warmer conditions are already leading to
      new species appearing in the Arctic, and these new species will tend
      to push existing species northward, likely eventually to extinction
      as the land ends and the Arctic Ocean begins.

      In addition, the melting of permafrost (and frozen sediments on the
      continental shelves) has the potential to release large amounts of
      methane (CH) that is tied up in hydrates. On a per molecule basis,
      methane is roughly 20 times as effective as trapping infrared
      radiation as is a CO2molecule, which is why there is so much
      attention being devoted to human-induced changes in methane
      concentrations (human contributions have caused about a 150% increase
      in the preindustrial CHconcentration). While permafrost melting has
      begun, determining how much CH4is being released has proven quite
      difficult and so the IPCC projections do not yet account for the
      potential warming influence of such releases, but the potential for
      substantial releases is quite significant, especially because warming
      in the Arctic is projected to be greater than for the world as a
      whole.

      Continued warming and changes in snowfall are also likely to further
      increase the ongoing retreat of mountain glaciers and the great ice
      sheets. In virtually all regions of the world, including on high
      tropical mountains, glaciers are retreating at a rapid rate. because
      the annual glacier runoff in many cases serves as water resources for
      wildlife and communities, the eventual loss of the glaciers is likely
      to have very significant consequences in many regions around the
      world. The area of the Greenland Ice Sheet that melts each year is
      also increasing, and satellite observations indicate that ice mass is
      decreasing.What appears to be happening is that rather than small
      puddles forming and then refreezing in the fall, larger puddles are
      forming, and then finding channels and crevasses to flow to the
      bedrock and eventually into the ocean, allowing a greater fraction of
      the increase in downward infrared radiation caused by the higher
      greenhouse gas concentrations to go into melting of ice as opposed to
      the very energy intensive process of evaporation of water. The
      situation is much like what would happen if one of those decorative
      ice statues on banquet tables were taken out of a freezer for longer
      and longer intervals-if out for only a short period, the thin
      meltwater layer on the statue might refreeze when the statue is put
      back in the freezer; however, if kept out longer, the meltwater
      created each time would be lost, and soon there would be no ice
      statue at all.

      Projections are that high-latitude warming of a few degrees Celsius
      (so perhaps 5F), which is projected for the second half of the
      21century, would be likely to lead to the melting of roughly half of
      the Greenland Ice Sheet over a period of up to several
      centuries,mirroring a similar event that occurred during the last
      interglacial,likely mainly as the result of a particular set of
      variations in the Earth's orbit at that time that brought comparable
      warmth to high northern latitudes. The effects on sea level of such
      extensive changes are discussed in the next section. While much of
      the above discussion has focused on the projected changes in seasonal
      to annual timescale changes, what really has most effect on people
      and the environment are the extremes of the weather that are combined
      to get the changes in the averages. The weather (i.e., the
      instantaneous state of the atmosphere) is determined by the
      interaction of all of the various forcings and gradients in the
      global system. Observations indicate that day-to-day weather
      conditions tend to vary about the mean conditions in a more-or-less
      standard way, creating a bell-shaped distribution of conditions with
      a few instances much above and below the average and a greater
      likelihood of the conditions being near the average expected at each
      time of year.

      The projected change in climate will shift this distribution, moving
      the average higher, and thereby creating a much greater likelihood
      that conditions will exceed a particular threshold (e.g., 90 or 95F).
      The likelihood of presently unusual events could also be changed if
      the shape of the bell-like distribution is changed, which could
      occur, for example, if the characteristics of the global circulation
      are changed (e.g., by moving the winter jet stream relative to
      mountain ranges such as the Himalayas, or by altering the oceans in
      ways that affect the irregular cycling or intensity of El Nino or La
      Nina events).

      As a result of the changes in climate, conditions such as heat waves
      (which exacerbate the heat index and thermal stress in cities ) and
      drought conditions favorable for wildfires are expected to become
      more frequent and more intense. In fact, Dai et al. (2004) calculate
      that the amount of land experiencing severe drought has more than
      doubled in the last 30 years, with almost half of the increase being
      due to rising temperatures rather than decreases in rainfall or
      snowfall.Not surprisingly, therefore, observations indicate that
      wildfires have been increasing on all continents, particularly
      sharply in North America, and projections are that this trend is
      likely to intensify with further increases in surface temperature.In
      addition, freeze events, which are important to controlling many
      types of pests and associated diseases, are projected to be less
      likely. As already mentioned, the occurrence of more intense and more
      frequent heavy rainfall events is likely to increase the occurrence
      of flooding. Analyses by Milly et al. (2002) indicate that the
      frequency of very large floods has increased substantially during the
      20century, which is consistent with climate model simulations, and
      modeling studies suggest that the trend will continue in the
      future.With respect to the potential severity of this type of effect,
      results from the Canadian climate modeling group cited in the US
      National Assessment indicate that the return period of what are now
      once in a hundred year events will, by the end of the century, likely
      be reduced to about once every 30 years, with even more severe events
      occurring once every hundred years. In that much of society's
      infrastructure is only designed to withstand once in a hundred year
      events, having more severe events occurring more often than once a
      century is likely to increase the likelihood of very damaging
      events,causing very adverse and costly impacts for both society and
      the environment.

      Some media reports and criticisms by skeptics question the rising
      concern about the increasing risks from more intense and more
      frequent occurrence of extreme weather events, indicating that no
      specific event can be attributed to global warming. To better
      understand the situation, consider the simple analogy of the Earth's
      weather being equivalent to a pot of slowly boiling water, with each
      bubble indicating an extreme event somewhere across the globe. If the
      heat under the pot is turned up, there will be more bubbles, some of
      which are the size of the previous largest bubble and perhaps some
      even larger. There is no way to say that any particular bubble was
      due to the increased heat or was bigger because of it, yet clearly
      the intensified bubbling is due to the additional heat. Now, the real
      world situation is further complicated by seasonal changes (roughly
      equivalent to the heat being slowly turned up and down, but each time
      to higher levels), spatial linkages resulting from the oceanic and
      atmospheric circulations (roughly equivalent to adding noodles to the
      boiling water), and the presence of mountains and other geographic
      features (roughly equivalent to having a pot of varying shape and
      thickness); as a result formally detecting the changes in extreme
      events is indeed a challenge. But there is no question that adding
      heat to the system will lead to greater extremes (were the subtropics
      not so warm, the incidence of tropical cyclones would be much less).

      Consequences at the Coastal Interface of the Terrestrial and Marine
      Environments

      At coastlines, the consequences of the changes in marine and
      terrestrial components come together. Because the coastal region
      provides habitat to so many species, from shrimp to shore birds, and
      from plant species to humans, past and projected changes occurring in
      this boundary environment have particular importance for the
      environment and society.

      Bays, inlets, estuaries, barrier islands, marshes, wetlands, and more
      provide habitat to a wide range of species, in some cases year-round
      and in other cases at particular times as species migrate from one
      region to another. These regions are breeding grounds for fish and
      fowl, and those, including humans, that live off of them. The
      particular conditions each species needs results from the balance
      between the saline ocean waters and the terrestrial freshwaters, all
      mixed by the tides and ocean currents and moderated and mixed by the
      particular weather conditions ranging from mild sea breezes to raging
      storms. Nutrients are provided by the oceanic and river flows and by
      atmospheric deposition, all then cycled through by the chain of
      living plants and animals (including both terrestrial and marine
      life). Productivity has been able to develop as a result of the
      relative stability of the shoreline environment, with niches being
      filled to make optimal use of available resources.

      Climate change is not the only stress that is now being imposed on
      this environment. Harvesting, air and water pollution, encroachment,
      toxics, excessive nitrogen deposition, oxygen deprivation, and more
      are all creating stresses, and now comes sea level rise and climate
      change (i.e., warming, changes in precipitation that alter runoff,
      intensified storms, changes in winds and ocean currents, and more).
      Sea level has been roughly stable for the past several thousand
      years, yet has recently begun to rise. Warming of ocean waters (which
      leads to their expansion, just as mercury expands to fill a
      thermometer as the temperature increases) and water added to the
      ocean, likely mostly from melting of mountain glaciers, caused global
      sea level to rise 4-8 inches (10-20 cm) during the 20century.For the
      21century, the early projections have been that sea level will go up
      by another 12-20 inches (30-50 cm);with the apparent acceleration in
      the melting of the Greenland Ice Sheet that has been observed,the
      Arctic Climate Impact Assessment concluded that projections of sea
      level rise for the 21century could quite possibly exceed 20 inches
      (50 cm), reaching toward the upper limit of the IPCC projections.
      What is particularly problematic is that the factors contributing the
      most to sea level rise, namely thermal expansion and the ultimate
      melting of the Greenland and West Antarctic Ice Sheets are likely to
      continue to contribute to sea level rise for centuries after the rise
      in greenhouse gases is halted, meaning that significant areas of the
      shoreline will be inundated and lost over coming decades and
      centuries, and that protection of the most valuable regions through
      levee construction needs to receive early attention.To date, no
      nation has prepared for sea level rise of a meter or more within a
      century, but the possibility warrants appropriate planning beyond
      normal disaster preparedness.

      While the rise in sea level itself might seem small, when amplified
      by the effects of storms creating waves and storm surges, the
      situation is particularly threatening. In the Arctic, the melting
      away from the shore of the sea ice away has allowed winter waves to
      pound the barrier islands, causing significant erosion. This is
      particularly a problem because coastal regions are where many native
      communities have been located, often for thousands of years, in order
      to harvest the bounty of both the land and the ocean. The most
      endangered community is currently Shishmaref, which is being eroded
      away so rapidly that community relocation has already started. As the
      Government Accountability Office has projected,relocation of all the
      endangered villages is going to be very costly. Both the climate
      changes themselves and the relocations will lead to substantial
      disruption of subsistence harvestingand indigenous culture and
      traditions that have sustained these communities through thousands of
      years.

      For coastal regions exposed to hurricanes and the waves and the storm
      surges that they create, the danger is also very great. While
      international assessments have generally suggested that developing
      countries are more vulnerable to global warming that developed
      nations because they lack the resources to be able to adapt, the
      developed nations have at risk far greater investments in coastal
      infrastructure, including roads, highways, railroads, airports,
      ports, sewage treatment facilities, and residential and commercial
      buildings. Many of these structures are fully exposed to the oceans,
      unlike New Orleans, which at least at one time was protected by
      extensive wetlands.

      With the power and duration of intense hurricanes observed to be
      increasing, and with greater changes likely ahead as ocean
      temperatures continue to rise, the coastal region is particularly at
      risk. While building levees is likely to be able to work for a while,
      if sea level rise reaches a few meters within a few centuries,
      retreat is ultimately going to be required in many regions.

      Disrupted coastlines are also likely to disrupt the resident and
      migrating wildlife. While some new wetlands may be formed further
      inland, it is unlikely that such new areas will be as extensive or as
      able to fill the many roles of existing areas, especially as the
      process of coastal inundation will be continuous rather than allowing
      full development at some altered, but fixed, change in sea level.

      Summary and Concluding Thoughts

      While the discussion above has focused on the great variety of
      changes and interactions that the increase in the COconcentration and
      changes in climate are leading to (and the above list is only a
      sampling), what will be experienced by the environment and society
      will be all of these changes together, plus the impacts of all of the
      other changes going on, ranging from air and water pollution to
      resource utilization and land cover change. While a number of these
      can be (and are being) ameliorated by regulations and policy, climate
      change presents several unique aspects. First, climate change will
      keep growing and growing-it is an influence that can only be slowed,
      not reversed (at least in any reasonable time horizon). Second, it is
      fully global, and because the world is environmentally and
      economically interconnected, impacts in one location can create
      impacts in other locations. And third, the changes are larger and
      occurring more rapidly than can be accounted for using any analogs to
      the past, making very real the potential for surprises, unexpected
      changes, unidentified thresholds, and tipping points. As Australian
      author and scientist Barrie Pittock has put it, "Uncertainty is
      inevitable, but risk is certain."

      For the natural world, change is already evident. Analyses by
      Parmesan and Yohe (2003) indicate with very high confidence that a
      large fraction of the plant and animal species studied are showing a
      response consistent with that expected to result from changes in
      climate.The types of responses include shifts in range (e.g., the
      Inuits are spotting types of birds never seen before that far north),
      changes in number and vitality (e.g., the polar bear population
      around Hudson's Bay), and unprecedented susceptibilities (e.g., to
      pest outbreaks). There is no question that the natural world is
      changing, and the main question is how much change can occur before
      changes in keystone species begin to cause the collapse of ecosystems
      (e.g., of the Amazon rainforest) and significant reductions in the
      ecosystem services (e.g., air and water purification, food and fiber
      generation, fish and shrimp production) that these systems provide to
      society. Of particular concern are how all of these changes affect
      migrating species from birds to butterflies and fish to whales, for
      they have generally developed a dependence on a timeline of resources
      at particular locations in order to survive, and significant loss
      could occur from substantial disruption of any of them.

      While modern society may seem less dependent on the natural world,
      many linkages remain, not only between communities and nearby
      ecosystems, but also with conditions around the world. Increased
      temperatures (along with higher absolute humidity-so much higher heat
      indices) will stress those not able to stay in and pay for air-
      conditioned space. While those in colder climates that have tight
      houses can readily transfer savings on heating bills to pay for
      increased cooling, those in more open homes in presently southern
      climates will have to invest in considerable structural upgrading to
      make air-conditioning a viable remedy. That the cost of upgrading
      will be high, and the need for it greatest among the poor, will
      create a serious issue of equity, with the least fortunate
      responsible for the lowest energy use yet suffering the largest
      consequences.

      The effects will not only be personal. Not only do modern societies
      draw resources and food from ecosystems and countries around the
      world, but products also come from around the world and investment
      portfolios typically include a mix of international stocks, coupling
      one's economic state to the state of the world. In addition, with
      people traveling extensively for business and pleasure, the health of
      people around the world is interconnected, and what happens in one
      location can soon affect those in other locations. In that warm
      conditions are generally more favorable for the presence of disease
      vectors such as mosquitoes, warming will lead to the loss of the ally
      of freezing conditions for helping to control mosquito populations.
      As a result, except in regions (such as the US) where rigorous public
      health practices and community building standards have over time
      separated the disease from the disease vector and from people,
      warming and increased precipitation are likely to exacerbate the
      likelihood of exposure to disease vectors.Even in countries such as
      the US, isolated occurrences are likely given the magnitude of
      international travel, and so extra resources will have to be devoted
      to maintaining high standards and quickly addressing new infestations
      (e.g., by spraying for mosquitoes).

      Changes in the distribution and level of activity of various plant
      species can also exacerbate health problems, as for example the
      increased production of pollen that can exacerbate incidence of
      asthma.The shifting climatic patterns and rising sea level are likely
      to be most problematic for small countries and other similarly sized
      entities. For island nations made up mainly of coral atolls, rising
      sea level and higher storm surges are already having deleterious
      effects on aquifers, and continuing sea level rise is likely to
      inundate several island nations over the coming century. For small
      countries, especially those that have focused on growing a particular
      crop, shifting climatic patterns are likely to require changes in
      crop species, which is likely to be difficult to compete as there
      will likely be the need to break into new markets. Whereas many
      indigenous peoples, including the American Indian, have long
      traditions of adaptation, at the root of previous successes was often
      the ability to relocate; with tribal reservations now fixed,
      community relocation is no longer possible, and medicinal plants and
      other historic species are likely to shift to quite removed
      locations, negating the passed on ecological wisdom developed over so
      many generations.

      For many regions, changes in water resources will be the most
      important effect, with increased competition for reduced resources
      among agricultural, community, industrial and ecological interests.
      For coastal regions, sea level rise and increases in storm intensity
      will pose the most important threats, requiring both enhancement of
      resilience in the near- term and possible relocation in the long-
      term. For those in urban areas, the increased likelihood of heat
      stress conditions and higher air pollution levelsmay well pose the
      most significant threat. Because the particular situation of each
      region will depend on its individual circumstances, as indicated in
      Table 1, it is vital that the nation have an ongoing assessment
      activity that helps regions and sectors to understand, prepare for,
      and ameliorate the most deleterious circumstances. Such an effort, as
      is called for in the Global Change Research Act of 1990 [P. L. 101-
      606], was begun in earnest in 1997 with the undertaking of the US
      National Assessment; that this effort was essentially terminated in
      2001 after having made significant progress in involving stakeholders
      in regional activities has been most unfortunate.

      What is most clear is that global climate change is underway and that
      the risk of adverse consequences for both marine and terrestrial
      environments is quite high. While it will take substantial efforts
      and many decades to limit emissions of greenhouse gases and bring
      climate change to a stop as called for in the UN Framework Convention
      on Climate Change ratified by the US Senate in 1992, that virtually
      no effort is being made by the US to accomplish this in the face of
      all the scientific information about impacts is most unfortunate. For
      the people of the Arctic and of the US whom I have had the privilege
      of representing in assessment activities, I urge your most urgent
      consideration of a national effort to prepare for the inevitable
      climate change that lies ahead and to take actions to sharply limit
      the climate change that will be brought on by future emissions.

      April 27, 2006

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