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Our results indicate that climate change will vary widely across the nation, those impacts will vary widely, as will our vulnerability to climate change. What do we mean by vulnerability? Vulnerability is defined as the magnitude of the climate impact after consideration of adaptation measures to lessen those impacts.
We appear to be particularly vulnerable to those impacts affecting natural ecosystems, but less vulnerable to those related to human-managed systems. We expect that the direct economic vulnerability is likely to be modest during the 21st Century for the kinds of climate scenarios we use in this assessment, but this, too, is likely to vary considerably from region to region.
The two principal climate scenarios for the 21st Century in the assessment can be briefly summarized as: one scenario is warm and wet and the other is hot and dry. Some of the gross features include annual average temperature increases of about 5 to 10 degrees Fahrenheit. This is about five to ten times the increase that has occurred during the 20th Century. Changes in total precipitation are less certain.
The CHAIRMAN. Have you ever seen changes like that before?
Mr. KARL. No. This would be an unprecedented change this century. In fact, the temperature increases during the 20th Century we now believe to be larger than anything we have seen in the last thousand years.
Changes in total precipitation are less certain, as indicated. For example, the wetter scenario has substantial increases in precipitation in the Southeast, about a 10- to 30-percent increase in precipitation. The drier scenario has about an equal decrease in precipitation.
There are other aspects of precipitation that we do have more certainty about. For example, all the climate scenarios and the observations suggest that more precipitation will occur in heavy and extreme precipitation events, as opposed to the light and moderate events.
All regions are affected by increases in the ability of the atmosphere to evaporate water from the surface as the temperature increases. This means that areas with marginal increases in precipitation are likely to be more vulnerable to more frequent extreme and severe drought. Other aspects of extreme weather, such as hurricane tracks, local severe weather, tornadoes, hail, et cetera, is still very uncertain.
The CHAIRMAN. I do not understand why an increase in severe weather would be associated with climate change.
Mr. KARL. Regarding the increase in heavy and extreme precipitation events, the best way to think about it is if you can imagine during the winter time in Alaska when you have precipitation, it falls in very light events. It is never very heavy. In converse, think about in the summertime, especially in the southern parts of the U.S., when it rains it rains very heavily, usually in short periods. This is the kind of trend that you will be seeing more frequently. We already see it in the observations. That is, precipitation tends to come in shorter bursts but heavier in magnitude.
With respect to some of the notable regional impacts around the nation, based on scenarios we used, I will just mention a few. In Alaska, sharp increases in temperature during the cold season are very likely to cause continued thawing of the permafrost, further disrupting the forest ecosystem, roads and buildings in that area. There is already considerable evidence in the observations that that has taken place.
In the Pacific Northwest there is likely to be more wintertime flooding and reduced spring flooding as snow pack decreases. Again the observations already show a significant decrease in snow, particularly in the West. This will put added stress on summer water supplies. Rising water temperatures will further complicate needed fish restoration efforts.
In the Midwest, at least for the next few decades, it is likely we will see a continued increase in agricultural production, in large part due to the fertilization effect of carbon dioxide on crops. We expect reductions in lake levels are also likely, increasing the cost of transportation in the lakes and down the rivers, ship and barge transportation. Increased water temperatures are likely to lead to increased eutrophication and reduced oxygen levels in lakes and rivers.
In the Northeast, climate change will very likely interact with many existing stresses in urban areas such as air quality, transportation, especially along the coast, due to rising sea level and storm surges, increased heat-related stresses, and effects on inflexible water supply systems.
Other stresses are likely to be mitigated. For example, snow removal costs and extreme cold winter exposures.
In the Southeast, generally the South does not reap the benefits of increased temperature for agricultural purposes, since temperatures are already quite warm. Along the Southeast gulf coast, inundation of coastal wetland is very likely to increase, threatening fertile areas for marine life, migrating birds, waterfowl.
In the hotter and drier scenario grasslands and savannahs replace the southernmost forests in the Southeast, while the warmer weather scenario expands the range of the southern tree species, and large increases in the heat index (the combination of temperature and humidity) average 10 to over 25 degrees Fahrenheit increases that will make summer outdoor activities quite stressful.
In the Great Plains, similar to the Midwest, higher CO2 concentrations are likely to offset the effects of rising temperatures, increasing agricultural yields and forest cover for several decades. Again, the southern portions of the Great Plains are not likely to reap these benefits.
In the West, both scenarios project a substantial increase in precipitation, leading to a reduction in desert ecosystems, being replaced by shrublands.
For our island States, more intense cycles of El Niño and la niña are possible, thereby increasing stresses on existing water supplies.
These are just a few of the impacts we discuss in the National Assessment. I just wanted to mention that there are many issues we are uncertain about, especially issues that are interdependent. These could be important, even though we do not understand them. Further assessments will need to address many of these interdependencies. Thank
you for the opportunity to make an opening statement. [The joint prepared statement of Mr. Karl, Dr. Melillo, and Dr. Janetos follow:]
JOINT PREPARED STATEMENT OF THOMAS R. KARL, DIRECTOR, NATIONAL CLIMATIC
DATA CENTER, NATIONAL ENVIRONMENTAL SATELLITE, DATA, AND INFORMATION SERVICE, NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION; DR. JERRY M. MELILLO, SENIOR SCIENTIST, ECOSYSTEMS CENTER, MARINE BIOLOGICAL LABORATORY; AND ANTHONY C. JANETOS, SENIOR VICE PRESIDENT FOR PROGRAM, WORLD RESOURCES INSTITUTE
We are very pleased to have the opportunity to address the Senate Committee on Commerce, Science, and Transportation on the topic of the potential impacts of climate variability and change on the U.S. Our draft assessment report, Climate Change Impacts on the United States: the Potential Consequences of Climate Variability and Change was released for a 60 day public comment period on Monday, June 12. It is an extensive synthesis of the best available scientific information on this important topic.
There are three questions about climate change that dominate discussions of this important topic. How much climate change is going to occur? What will happen as a result? What can countries do about it? There are obviously heated political opinions about each of these, but the issues are real, and it is critical to understand the underlying scientific knowledge about each if sound decisions are to be made. The assessment report focuses on the second of these questions.
A national assessment of the potential impacts of climate change was called for in the 1990 legislation that established the U.S. Global Change Research Program (USGCRP). For several years, the research program focused on developing the basic scientific knowledge that the international scientific assessment process overseen by the Intergovernmental Panel on Climate Change (IPCC) depends on. The IPCC was jointly established by the World Meteorological Organization and the United Nations Environmental Programme in 1988. As scientific research has provided compelling evidence that climate change is in fact occurring, it has become increasingly clear that there is a need to understand what is at stake for natural resources and human well-being in the U.S. In response to this need, in 1998, Dr. John H. Gibbons, then Science Advisor to the President, requested the USGCRP to undertake the national assessment originally called for in the legislation. Dr. Gibbons asked the USGCRP to investigate a series of important questions: • What are the current environmental stresses and issues for the United States
that form a backdrop for additional impacts of climate change? • How might climate change and variability exacerbate or ameliorate existing
problems? • What are the priority research and information needs that can better prepare
policy makers for making wise decisions related to climate change and variability? What information and answers to what key questions could help decision-makers make better-informed decisions about risk, priorities, and re
sponses? What are the potential obstacles to information transfer? • What research is most important to complete over the short term? Over the
long term? • What coping options exist that can build resilience to current environmental
stresses, and also possibly lessen the impacts of climate change? How can we simultaneously build resilience and flexibility for the various sectors considering
both the short and long-term implications? • What natural resource planning and management options make most sense in
the face of future uncertainty?
• What choices are available for improving our ability to adapt to climate change
and variability and what are the consequences of those choices? How can we improve contingency planning? How can we improve criteria for land acquisi
tion? A variety of efforts emerged in response to Dr. Gibbons' charge.
Over twenty workshops were held around the country, involving academics, business-people representing a range of industries including manufacturing, power generation and tourism, and people who work closely with land and water ecosystems including resource managers, ranchers, farmers, foresters and fishermen. Each workshop identified a range of issues of concern to stakeholders in those regions, many of them quite unrelated to climate change, per se. Most workshops were followed by the initiation of scientific, university-led regional studies, some of which have finished their work, and others of which are ongoing.
In addition to these kind of "bottom-up” efforts, it was decided that it was also necessary to create a national-level synthesis of what is known about the potential for climate impacts for the U.S. as a whole, addressing the issues identified in the regional workshops and national studies. This synthesis obviously needed to build on the work that had begun to emerge from the subsequent regional and national studies, but also to draw on the existing scientific literature and analyses done with the most up-to-date ecological and hydrological models and data that could be obtained. The National Assessment Synthesis Team (NAST) was established by the National Science Foundation as an independent committee under the Federal Advisory Committee Act (FACA) specifically in order to carry out this second step. This committee is made up of experts from academia, industry, government laboratories, and non-governmental organizations (NGO's) (membership list is Attachment 1). In order to ensure openness and independence, all meetings of the NAST have been open to the public, all documents discussed in its meetings are available through the National Science Foundation, as are all the review comments already received and responses to them. This is perhaps out of the ordinary for a scientific study; but most scientific studies do not focus on issues of such broad and deep implications for American society, and about which there is such heated rhetoric.
The NAST's first action was to publish a plan for the conduct of the national synthesis. In addition, five issues (agriculture, water, forests, health, and coastal and marine systems), out of the many identified, were later selected by the National Synthesis Assessment Team (NAST) to be topics for national studies. Carrying out this plan has been a major undertaking. The end result has been the production of a comprehensive two-volume National Assessment Report, available to the public for a 60-day comment period. The “Foundation" volume is more than 600 pages long, with more than 200 figures and tables, with analyses of the five national sectors, and 9 regions that together cover the entire U.S. It is extensively referenced, and a commitment has been made that all sources used in its preparation are open and publicly available. The “Overview” volume is about 150 pages long, written in a style that is more accessible to the lay public, and summarizes the Foundation in a way that we hope will be understandable and informative, and which we are confident is scientifically sound. Both documents have already been through extensive review. At the end of 1999, two rounds of technical peer review were undertaken, and during the past spring, an additional review by about 20 experts outside the assessment process was undertaken. Over 300 sets of comments have been received from scientists in universities, industry, NGO's, and government laboratories. The responses to all external comments have been described in comprehensive review memorandums. We are now in the final stage of the process, a 60 day public comment period specifically requested by Congress, after which final revisions will be done and the report submitted to the President and Congress, as called for in the original legislation.
In order to ensure that the NAST has undertaken its charge well, an oversight panel was also established through the offices of the President's Council of Advisors on Science and Technology (membership list is Attachment 2). The oversight panel is chaired by Dr. Peter Raven, Director of the Missouri Botanical Garden and recently retired Home Secretary of the National Academy of Sciences, and Dr. Mario Molina, Professor of Atmospheric Chemistry at MIT, and recent Nobel-prize winner for his research on stratospheric ozone depletion. Its membership, like the NAST's, is drawn from academia, industry, and NGO's. It has reviewed and approved of the plans for the assessment, reviewed each draft of the report, and reviewed the response of the NAST to all comments.
What have been the results of this extraordinarily open process? What assumptions drive the analysis? What conclusions have been reached?
It is important to realize that the national assessment does not attempt to predict exactly what the future will hold for the U.S. It has examined the potential implications of two primary climate scenarios, each based on the same assumptions about future "business as usual” global emissions of greenhouse gases that the IPCC has used for many of its analyses. The two climate scenarios were based on output from two different global climate models used in the IPCC assessment. They are clearly within the range of global annual average temperature changes shown by many such models, one near the low and one near the high end of the range. Both exhibit warming trends for the U.S. that are larger than the global average (Attachment 3). This is not surprising. For many years, one of the most robust results of global climate models has been that greater warming is expected in more northerly latitudes, and that land surfaces are expected to warm more than the global average. We have used assumptions that are entirely consistent with those used by the IPCC.
These climate scenarios describe significantly different futures that are all scientifically plausible, given our current understanding of how the climate system op; erates. As importantly, they describe separate baselines for analysis of how natural ecosystems, agriculture, water supplies, etc. might change as a result. In order to investigate such changes, i.e. the potential impacts of climate changes, the report relies on up-to-date models, on empirical observations from the literature, on investigations of how these systems have responded to climate variability that has been observed over the past century in the U.S., and on the accumulated scientific knowledge that is available about the sensitivities of resources to climate, and about how the regions of the U.S. have and potentially could respond.
One additional important point about the scenarios should be mentioned. The report does not “merge” the results of models that disagree; it explicitly avoids doing so. The best example of this is in the analysis of potential changes in precipitation, where the two models used to create the scenarios give quite different results for some areas of the U.S. We have chosen to highlight these differences and explain that regional-scale precipitation projections are much more uncertain compared with temperature, rather than attempting to merge the results or guess which is more likely. The knowledge that th direction of precipitation change in some areas is quite uncertain is valuable for planning purposes, and clearly represents an important research challenge. There is however, consistency among models and observations on other aspects of precipitation changes. For example, both models and observations show an increase in the proportion of precipitation derived from heavy and extreme events as the climate warms (Attachment 4). So, both types of information are pertinent to help with the identification of potential coping actions. In this respect, the report follows the procedure that the IPCC itself uses for its global impacts reports, each of which examines the potential impacts for entire continents.
The U.S. national assessment presents the results for each scenario clearly, and then takes the important additional step, of explicitly describing the NAST's scientific judgment about the uncertainty inherent in each result. Those results that are viewed to be robust are described in more terms; those viewed to be the result of poorly understood or unreconciled differences between models are described in more circumspect language. The lexicon of terms used to denote the NAST's greater or lesser confidence is explicitly described in the beginning of the Overview report. This helps ensure that the report does not mask important results by thoughtlessly merging models, or overstating the scientific capability for assessing potential impacts. Finally, the report begins to identify possible options for adaptation to this changing world. It does not do a complete analysis of the costs, benefits, or feasibility of these options however, which is a necessary next step for developing policies to address these issues.
The report's draft key findings (as more fully described in Attachment 5) present important observations for all Americans: 1. Increased warming. Assuming continued growth in world greenhouse gas
emissions, the climate models used in this Assessment project that tempera
tures in the U.S. will rise 5–10°F (3-6°C) on average in the next 100 years. 2. Differing regional impacts. Climate change will vary widely across the U.S.
Temperature increases will vary somewhat from one region to the next. Heavy and extreme precipitation events are likely to become more frequent, yet some regions will get drier. The potential impacts of climate change will
also vary widely across the nation. 3. Vulnerable ecosystems. Ecosystems are highly vulnerable to the projected rate
and magnitude of climate change. A few, such as alpine meadows in the Rocky Mountains and some barrier islands, are likely to disappear entirely,