CanadaABSTRACTS - CLIMATE CHANGE AND THE UNITED STATES

Chen, Chi-Chung, Dhazn Gillig, and Bruce A. McCarl. 2001. "Effects of Climatic Change on a Water Dependent Regional Economy: A Study of the Texas Edwards Aquifer," Climatic Change, Vol. 49, No. 4, June, pp. 397-409.
ABSTRACT: Global climate change portends shifts in water demand and availability which may damage or cause intersectoral water reallocation in water short regions. This study investigates effects of climatic change on regional water demand and supply as well as the economy in the San Antonio Texas Edwards Aquifer region. This is done using a regional model which portrays both hydrological and economic activities. The overall results indicate that changes in climatic conditions reduce water resource availability and increase water demand. Specifically, a regional welfare loss of $2.2-$6.8 million per year may occur as a result of climatic change. Additionally, if springflows are to be maintained at the currently desired level to protect endangered species, pumping must be reduced by 9-20% at an additional cost of $0.5 to $2 million per year

Thomson, Allison M., Robert A. Brown, Steven J. Ghan, et al. 2002. "Elevation Dependence of Winter Wheat Production in Eastern Washington State with Climate Change: A Methodological Study," Climatic Change, Vol. 54, No. 1-2, July, pp. 141-164.
ABSTRACT: Crop growth models, used in climate change impact assessments to project production on a local scale, can obtain the daily weather information to drive them from models of the Earth's climate. General Circulation Models (GCMs), often used for this purpose, provide weather information for the entire globe but often cannot depict details of regional climates especially where complex topography plays an important role in weather patterns. The U.S. Pacific Northwest is an important wheat growing region where climate patterns are difficult to resolve with a coarse scale GCM. Here, we use the PNNL Regional Climate Model (RCM) which uses a sub-grid parameterization to resolve the complex topography and simulate meteorology to drive the Erosion Productivity Impact Calculator (EPIC) crop model. The climate scenarios were extracted from the PNNL-RCM baseline and 2 × CO2 simulations for each of sixteen 90 km2 grid cells of the RCM, with differentiation by elevation and without correction for climate biases. The dominant agricultural soil type and farm management practices were established for each grid cell. Using these climate and management data in EPIC, we simulated winter wheat production in eastern Washington for current climate conditions (baseline) and a 2 × CO2 `greenhouse' scenario of climate change. Dryland wheat yields for the baseline climate averaged 4.52 Mg ha-1 across the study region. Yields were zero at high elevations where temperatures were too low to allow the crops to mature. The highest yields (7.32 Mg ha-1) occurred at intermediate elevations with sufficient precipitation and mild temperatures. Mean yield of dryland winter wheat increased to 5.45 Mg ha-1 for the 2 × CO2 climate, which was markedly warmer and wetter. Simulated yields of irrigated wheat were generally higher than dryland yields and followed the same pattern but were, of course, less sensitive to increases in precipitation. Increases in dryland and irrigated wheat yields were due, principally, to decreases in the frequency of temperature and water stress. This study shows that the elevation of a farm is a more important determinant of yield than farm location in eastern Washington and that climate changes would affect wheat yields at all farms in the study.

Agriculture

Reilly, J., F. Tubiello, B. McCarl, D. Abler, R. Darwin, et al. 2003. "U.S. Agriculture and Climate Change: New Results," Climatic Change, Vol. 57, pp. 43-69.
PDF: http://www.giss.nasa.gov/gpol/docs/2003/2003_ReillyTubiello.pdf.
ABSTRACT: We examined the impacts on U.S. agriculture of transient climate change as simulated by 2 global general circulation models focusing on the decades of the 2030s and 2090s. We examined historical shifts in the location of crops and trends in the variability of U.S. average crop yields, finding that non-climatic forces have likely dominated the north and westward movement of crops and the trends in yield variability. For the simulated future climates we considered impacts on crops, grazing and pasture, livestock, pesticide use, irrigation water supply and demand, and the sensitivity to international trade assumptions, finding that the aggregate of these effects were positive for the U.S. consumer but negative, due to declining crop prices, for producers. We examined the effects of potential changes in El Niño/Southern Oscillation (ENSO) and impacts on yield variability of changes in mean climate conditions. Increased losses occurred with ENSO intensity and frequency increases that could not be completely offset even if the events could be perfectly forecasted. Effects on yield variability of changes in mean temperatures were mixed. We also considered case study interactions of climate, agriculture, and the environment focusing on climate effects on nutrient loading to the Chesapeake Bay and groundwater depletion of the Edward's Aquifer that provides water for municipalities and agriculture to the San Antonio, Texas area. While only case studies, these results suggest environmental targets such as pumping limits and changes in farm practices to limit nutrient run-off would need to be tightened if current environmental goals were to be achieved under the climate scenarios we examined.

Abler, David, James Shortle, Jeffrey Carmichael, and Richard Horan. 2002. "Climate Change, Agriculture, and Water Quality in the Chesapeake Bay Region," Climatic Change, Vol. 55, No. 3, November, pp. 339-359.
ABSTRACT: Research on climate change and agriculture has largely focused on production, food prices, and producer incomes. However, societal interest in agriculture is much broader than these issues. The objective of this paper is to analyze the potential impacts of climate change on an important negative externality from agriculture, water quality. We construct a simulation model of maize production in twelve watersheds within the U.S. Chesapeake Bay Region that has economic and watershed components linking climate to productivity, production decisions by maize farmers, and nitrogen loadings delivered to the Chesapeake Bay. Maize is an important crop to study because of its importance to the region's agriculture and because it is a major source of nutrient pollution. The model is run under alternative scenarios regarding the future climate, future baseline (without any climate change), whether farmers respond to climate change, whether there are carbon dioxide (CO2) enrichment effects on maize production, and whether agricultural prices facing the region change due to climate change impacts on global agricultural commodity markets. The simulation results differ from one scenario to another on the magnitude and direction of change in nitrogen deliveries to the Chesapeake Bay. The results are highly sensitive to the choice of future baseline scenario and to whether there are CO2 enrichment effects. The results are also highly sensitive to assumptions about the impact of climate change on commodity prices facing farmers in the Chesapeake Bay region. The results indicate that economic responses by farmers to climate change definitely matter. Assuming that farmers do not respond to changes in temperature, precipitation, and atmospheric CO2 levels could lead to mistaken conclusions about the magnitude and direction of environmental impacts.

Rosenzweig, Cynthia, Francesco N. Tubiello, Richard Goldberg, Evan Mills, and Janine Bloomfield. 2002. "Increased crop damage in the US from excess precipitation under climate change," Global Environmental Change, Vol. 12, No. 3, October, pp. 197-202.
PDF: http://eetd.lbl.gov/EMills/PUBS/PDF/Crops_GEC.pdf.
ABSTRACT: Recent flooding and heavy precipitation events in the US and worldwide have caused great damage to crop production. If the frequency of these weather extremes were to increase in the near future, as recent trends for the US indicate and as projected by global climate models (e.g., US National Assessment, Overview Report, 2001, The Potential Consequences of Climate Variability and Change, National Assesment Synthesis Team, US Global Change Research Program, Washington, DC; Houghton et al., 2001, IPCC Climate Change 2001: The Scientific Basis, Third Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, 335pp.), the cost of crop losses in the coming decades could rise dramatically. Yet current assessments of the impacts of climate change on agriculture have not quantified the negative effects on crop production from increased heavy precipitation and flooding (Impacts of climate change and variability on agriculture, in: US National Assessment Foundation Document, 2001. National Assessment Synthesis Team, US Global Change Research Program, Washington DC.). In this work, we modify a dynamic crop model in order to simulate one important effect of heavy precipitation on crop growth, plant damage from excess soil moisture. We compute that US corn production losses due to this factor, already significant under current climate, may double during the next thirty years, causing additional damages totaling an estimated $3 billion per year. These costs may either be borne directly by those impacted or transferred to private or governmental insurance and disaster relief programs.

Southworth, Jane, R. A. Pfeifer, M. Habeck, et al. 2002. "Changes in Soybean Yields in the Midwestern United States as a Result of Future Changes in Climate, Climate Variability, and CO2 Fertilization," Climatic Change, Vol. 53, No. 4, pp. 447-475.
ABSTRACT: This modeling study addresses the potential impacts of climate change and changing climate variability due to increased atmospheric CO2 concentration on soybean (Glycine max (L.) Merrill) yields in the Midwestern Great Lakes Region. Nine representative farm locations and six future climate scenarios were analyzed using the crop growth model SOYGRO. Under the future climate scenarios earlier planting dates produced soybean yield increases of up to 120% above current levels in the central and northern areas of the study region. In the southern areas, comparatively small increases (0.1 to 20%) and small decreases (-0.1 to -25%) in yield are found. The decreases in yield occurred under the Hadley Center greenhouse gas run (HadCM2-GHG), representing a greater warming, and the doubled climate variability scenario - a more extreme and variable climate. Optimum planting dates become later in the southern regions. CO2 fertilization effects (555 ppmv) are found to be significant for soybean, increasing yields around 20% under future climate scenarios. For the study region as a whole the climate changes modeled in this research would have an overall beneficial effect, with mean soybean yield increases of 40% over current levels.

Tubiello, F.N., C. Rosenzweig, R.A. Goldberg, S. Jagtap, and J.W. Jones. 2002. "Effects of climate change on U.S. crop production: Simulation results using two different GCM scenarios. Part I: Wheat, potato, maize, and citrus," Climate Research, Vol. 20, pp. 259-270.
ABSTRACT: We projected U.S. agricultural production in 2030 and 2090 at 45 representative sites, using two scenarios of climate change -- developed with the Hadley Centre Model and the Canadian Centre Climate Model -- and the DSSAT (Decision Support Systems for Agro-technology Transfer) dynamic crop-growth models. These simulation results have previously been aggregated nationally with the aid of economic models, to show an increase in overall U.S. agricultural output under climate change. In this work, we analyzed the regional distribution of the simulated yields, showing that positive results largely depend on the precipitation increases projected by the climate scenarios. In contrast, in some important rain-fed production areas where precipitation was projected to decrease, such as the Kansas and Oklahoma Bread Basket regions under the Canadian Centre Climate Model scenario, climate change resulted in significant reductions of grain yield (in the range -30% to -40%), accompanied by increased year-to-year variability. We also discussed the response to additional factors affecting the simulated U.S. crop production under climate change, such as higher temperature and elevated CO2.

Mearns, L. O., W. Easterling, C. Hays, and D. Marx. 2001. "Comparison of Agricultural Impacts of Climate Change Calculated from High and Low Resolution Climate Change Scenarios: Part I. The Uncertainty Due to Spatial Scale," Climatic Change, Vol. 51, No. 2, November, pp. 131-172.
ABSTRACT: We investigated the effect of two different spatial scales of climate change scenarios on crop yields simulated by the EPIC crop model for corn, soybean, and wheat, in the central Great Plains of the United States. The effect of climate change alone was investigated in Part I. In Part II (Easterling et al., 2001) we considered the effects of CO2 fertilization effects and adaptation in addition to climate change. The scenarios were formed from five years of control and 2 × CO2 runs of a high resolution regional climate model (RegCM) and the same from an Australian coarse resolution general circulation model (GCM), which provided the initial and lateral boundary conditions for the regional model runs. We also investigated the effect of two different spatial resolutions of soil input parameters to the crop models. We found that for corn and soybean in the eastern part of the study area, significantly different mean yield changes were calculated depending on the scenario used. Changes in simulated dryland wheat yields in the western areas were very similar, regardless of the scale of the scenario. The spatial scale of soils had a strong effect on the spatial variance and pattern of yields across the study area, but less effect on the mean aggregated yields. We investigated what aspects of the differences in the scenarios were most important for explaining the different simulated yield responses. For instance, precipitation changes in June were most important for corn and soybean in the eastern CSIRO grid boxes. We establish the spatial scale of climate change scenarios as an important uncertainty for climate change impacts analysis.

Easterling, W. E., L. O. Mearns, C. J. Hays, and D. Marx. 2001. "Comparison of Agricultural Impacts of Climate Change Calculated from High and Low Resolution Climate Change Scenarios: Part II. Accounting for Adaptation and CO2 Direct Effects," Climatic Change, Vol. 51, No. 2, November, pp. 173-197.
ABSTRACT: We assert that the simulation of fine-scale crop growth processes and agronomic adaptive management using coarse-scale climate change scenarios lower confidence in regional estimates of agronomic adaptive potential. Specifically, we ask: 1) are simulated yield responses to low-resolution climate change, after adaptation (without and with increased atmospheric CO2), significantly different from simulated yield responses to high-resolution climate change, after adaptation (without and with increased atmospheric CO2)? and 2) does the scale of the soils information, in addition to the scale of the climate change information, affect yields after adaptation? Equilibrium (1 × CO2 versus 2 × CO2) climate changes are simulated at two different spatial resolutions in the Great Plains using the CSIRO general circulation model (low resolution) and the National Center for Atmospheric Research (NCAR) RegCM2 regional climate model (high resolution). The EPIC crop model is used to simulate the effects of these climate changes; adaptations in EPIC include earlier planting and switch to longer-season cultivars. Adapted yields (without and with additional carbon dioxide) are compared at the different spatial resolutions. Our findings with respect to question 1 suggest adaptation is more effective in most cases when simulated with a higher resolution climate change than its more generalized low resolution equivalent. We are not persuaded that the use of high resolution climate change information provides insights into the direct effects of higher atmospheric CO2 levels on crops beyond what can be obtained with low resolution information. However, this last finding may be partly an artifact of the agriculturally benign CSIRO and RegCM2 climate changes. With respect to question 2, we found that high resolution details of soil characteristics are particularly important to include in adaptation simulations in regions typified by soils with poor water holding capacity.

Southworth, Jane, J. C. Randolpha, M. Habeckb, O. C. Doeringb, R. A. Pfeifer, et al. 2000. "Consequences of future climate change and changing climate variability on maize yields in the midwestern United States," Agriculture, Ecosystems & Environment, Vol. 82, No. 1-3 , December, pp. 139-158.
ABSTRACT: Any change in climate will have implications for climate-sensitive systems such as agriculture, forestry, and some other natural resources. With respect to agriculture, changes in solar radiation, temperature, and precipitation will produce changes in crop yields, crop mix, cropping systems, scheduling of field operations, grain moisture content at harvest, and hence, on the economics of agriculture including changes in farm profitability. Such issues are addressed for 10 representative agricultural areas across the midwestern Great Lakes region, a five-state area including Indiana, Illinois, Ohio, Michigan, and Wisconsin. This region is one of the most productive and important agricultural regions in the world, with over 61% of the land use devoted to agriculture.
Individual crop growth processes are affected differently by climate change. A seasonal rise in temperature will increase the developmental rate of the crop, resulting in an earlier harvest. Heat stress may result in negative effects on crop production. Conversely, increased rainfall in drier areas may allow the photosynthetic rate of the crop to increase, resulting in higher yields. Properly validated crop simulation models can be used to combine the environmental effects on crop physiological processes and to evaluate the consequences of such influences. With existing hybrids, an overall pattern of decreasing crop production under scenarios of climate change was found, due primarily to intense heat during the main growth period. However, the results changed with the hybrid of maize (Zea mays L.) being grown and the specific location in the study region. In general, crops grown in sites in northern states had increased yields under climate change, with those grown in sites in the southern states of the region having decreased yields under climate change. Yields from long-season maize increased significantly in the northern part of the study region under future climate change. Across the study region, long-season maize performed most successfully under future climate scenarios compared to current yields, followed by medium-season and then short-season varieties. This analysis highlights the spatial variability of crop responses to changed environmental conditions. In addition, scenarios of increased climate variability produced diverse yields on a year-to-year basis and had increased risk of a low yield. Results indicate that potential future adaptations to climate change for maize yields would require either increased tolerance of maximum summer temperatures in existing maize varieties or a change in the maize varieties grown.

Brown, Robert A., and Norman J. Rosenberg. 1999. "Climate Change Impacts on the Potential Productivity of Corn and Winter Wheat in Their Primary United States Growing Regions," Climatic Change, Vol. 41, No. 1, January, pp. 73-107.
ABSTRACT: We calculate the impacts of climate effects inferred from three atmospheric general circulation models (GCMs) at three levels of climate change severity associated with change in global mean temperature (GMT) of 1.0, 2.5 and 5.0 °C and three levels of atmospheric CO2 concentration ([CO2]) - 365 (no CO2 fertilization effect), 560 and 750 ppm - on the potential production of dryland winter wheat (Triticum aestivum L.) and corn (Zea mays L.) for the primary (current) U.S. growing regions of each crop. This analysis is a subset of the Global Change Assessment Model (GCAM) which has the goal of integrating the linkages and feedbacks among human activities and resulting greenhouse gas emissions, changes in atmospheric composition and resulting climate change, and impacts on terrestrial systems. A set of representative farms was designed for each of the primary production regions studied and the Erosion Productivity Impact Calculator (EPIC) was used to simulate crop response to climate change. The GCMs applied were the Goddard Institute of Space Studies (GISS), the United Kingdom Meteorological Transient (UKTR) and the Australian Bureau of Meteorological Research Center (BMRC), each regionalized by means of a scenario generator (SCENGEN). The GISS scenarios have the least impact on corn and wheat production, reducing national potential production for corn by 6% and wheat by 7% at a GMT of 2.5 °C and no CO2 fertilization effect; the UKTR scenario had the most severe impact on wheat, reducing production by 18% under the same conditions; BMRC had the greatest negative impact on corn, reducing production by 20%. A GMT increase of 1.0°C marginally decreased corn and wheat production. Increasing GMT had a detrimental impact on both corn and wheat production, with wheat production suffering the greatest losses. Decreases for wheat production at GMT 5.0 and [CO2] = 365 ppm range from 36% for the GISS to 76% for the UKTR scenario. Increases in atmospheric [CO2] had a positive impact on both corn and wheat production. AT GMT 1.0, an increase in [CO2] to 560 ppm resulted in a net increase in corn and wheat production above baseline levels (from 18 to 29% for wheat and 2 to 5% for corn). Increases in [CO2] help to offset yield reductions at higher GMT levels; in most cases, however, these increases are not sufficient to return crop production to baseline levels.

Giorgi, Filippo, Linda O. Mearns, Christine Shields, and Larry McDaniel. 1998. "Regional Nested Model Simulations of Present Day and 2 × CO2 Climate over the Central Plains of the U.S.," Climatic Change, Vol. 40. No. 3-4, December, pp. 457-493.
ABSTRACT: A nested regional climate model is used to generate a scenario of climate change over the MINK region (Missouri, Iowa, Nebraska, Kansas) due to doubling of carbon dioxide concentration (2 × CO2) for use in agricultural impact assessment studies. Five-year long present day (control) and 2 × CO2 simulations are completed at a horizontal grid point spacing of 50 km. Monthly and seasonal precipitation and surface air temperature over the MINK region are reproduced well by the model in the control run, except for an underestimation of both variables during the spring months. The performance of the nested model in the control run is greatly improved compared to a similar experiment performed with a previous version of the nested modeling system by Giorgi et al. (1994). The nested model generally improves the simulation of spatial precipitation patterns compared to the driving general circulation model (GCM), especially during the summer. Seasonal surface warming of 4 to 6 K and seasonal precipitation increases of 6 to 24% are simulated in 2 × CO2 conditions. The control run temperature biases are smaller than the simulated changes in all seasons, while the precipitation biases are of the same order of magnitude as the simulated changes. Although the large scale patterns of change in the driving GCM and nested RegCM model are similar, significant differences between the models, and substantial spatial variability, occur within the MINK region.

Rosenzweig, C., J. Phillips, R. Goldberg, J. Carroll, and T. Hodges. 1996. "Potential impacts of climate change on citrus and potato production in the US," Agricultural Systems, Vol. 52, pp. 455-479.
ABSTRACT: Potential impacts of global climate change on fruit and vegetable yield in the US were investigated through simulations of citrus and potato. Simulated treatments included combinations of three increased temperature regimes (+1.5, +2.5, and 5.0°C), and estimates of the impact of three levels of atmospheric carbon dioxide (440, 530, and 660 ppm) in addition to control runs representing current climatic conditions. Adaptive planting dates of -28, -14, +14 and +28 dayes were included in the potato simulations for current and increased temperature regimes. Twenty-two sites were simulated for citrus yields and 12 sites for potato, using climate records for 1951 to 1980. Response surfaces were developed for all combinations of increased temperature and CO2. Results of citrus simulations without CO2-induced yield improvement indicate that production may shift slightly northward in the southern states, but yields may decline in southern Florida and Texas due to excessive heat during the winter. CO2 effects tended to counteract the decline in simulated citrus yields. Fall potato production under current management practices appears vulnerable to an increase in temperature in the northern states; increased CO2 and changes in planting date were estimated to have minimal compensating impacts on simulated potato yields.

Adams, R.M., R.A. Fleming, C.-C. Chang, B.A. McCarl, and C. Rosenzweig. 1995. "A reassessment of the economic effects of global climate change on U.S. agriculture," Climatic Change, Vol. 30, pp. 147-167.
ABSTRACT: This study uses recent GCM forecasts, improved plant science and water supply data and refined economic modeling capabilities to reassess the economic consequences of long-term climatic change on U.S. agriculture. Changes to crop yields, crop water demand and irrigation water arising from climatic change result in changes in economic welfare. Economic consequences of the three GCM scenarios are mixed; GISS and GFDL-QFlux result in aggregate economic gains, UKMO implies losses. As in previous studies, the yield enhancing effects of atmospheric CO2 are an important determinant of potential economic consequences. Inclusion of changes in world food production and associated export changes generally have a positive effect on U.S. agriculture. As with previous studies, the magnitude of economic effects estimated here are a small percentage of U.S. agricultural value.

Rosenzweig, C., and D. Hillel. 1993. "The Dust Bowl of the 1930s: Analog of greenhouse effect in the Great Plains?," Journal of Environmental Quality, Vol. 22, pp. 9-22.
ABSTRACT: For nine sites in the southern Great Plains, the decade of the Dust Bowl was consistently warmer than the 1951 to 1980 "normal." It also tended to be drier, but less consistently so. At four of the nine sites, the combination of consistently higher temperatures and mostly lower precipitation had a cumulative effect over the 1930s, making the entire decade a period of agricultural drought as characterized by the Palmer Drought Severity Index (PDSI). Episodes of extreme drought occurred at many sites, particularly in 1934 in Nebraska. Temperature and precipitation changes predicted by two general circulation models (GCMs) at the upper range of current climate model predictions for doubled concentrations of CO2 (+4.2°C and +4.0°C mean global surface air temperature warming) suggest drought conditions as defined by the PDSI that are worse than those for the 1930s for all stations. Droughtiness is projected to increase overall, even when the GCM climate change scenarios produce little change or even increases in precipitation. In most instances, the mean GCM-predicted drought conditions equal or exceed the extreme drought years of the decade. When dynamic crop growth models were run in combination with the GCM-predicted climates, simulated wheat (Triticum aestivum L.) and corn (Zea mays L.) yields were obtained that were generally lower (~30%) than those of simulations for the actual climate of the 1930s. The crop model simulations indicated that the predicted climate change is likely to be less detrimental to a crop such as wheat, whose main growing period is in the spring, than to a typical summer crop such as corn. The overall results of this study suggest that the Dust Bowl experience of the 1930s may be characterized as a preliminary analog of possible future climate conditions for the southern Great Plains, with the important difference that the higher projections of GCM warming produce more severe climatic consequences than the Dust Bowl.

Adams, R.M., C. Rosenzweig, R.M. Peart, J.T. Ritchie, B.A. McCarl, et al. 1990. "Global climate change and U.S. agriculture," Nature, Vol. 345, pp. 219-224.
ABSTRACT: Agricultural productivity is expected to be sensitive to global climate change. Models from atmospheric science, plant science, and agricultural economics are linked to explore this sensitivity. Although the results depend on the severity of climate change and the compensating effects of carbon dioxide on crop yields, the simulation suggests that irrigated acreage will expand and regional patterns of U.S. agriculture will shift. The impact on the U.S. economy strongly depends on which climate model is used.

Rosenzweig, C. 1985. "Potential CO2-induced climate effects on North American wheat-producing regions," Climatic Change, Vol. 7, pp. 367-389.
ABSTRACT: The environmental requirements for growth of winter, spring, and fall-sown spring wheats in North America are specified and compared to temperature results from the control run of the Goddard Institute for Space Studies general circulation model (GISS GCM) and observed precipitation in order to generate a simulated map of current wheat production regions. The simulation agrees substantially with the actual map of wheat-growing regions in North America. Results from a doubled CO2 run of the climate model are then used to generate wheat regions under the new climatic conditions. In the simulation, areas of production increase in North America, particularly in Canada, due to increased growing degree units (GDU). Although wheat classifications may change, major wheat regions in the United States remain the same under simulated doubled CO2 conditions. The wheat-growing region of Mexico is identified as vulnerable due to high temperature stress. Higher mean temperatures during wheat growth, particularly during the reproductive stages, may increase the need for earlier-maturing, more heat-tolerant cultivars throughout North America. The soil moisture diagnostic of the climate model is used to analyze potential water availability in the major wheat region of the Southern Great Plain.

Coastal and Marine Resources

Yohe, Gary W., and Michael E. Schlesinger. 1998. "Sea-Level Change: The Expected Economic Cost of Protection Or Abandonment in the United States," Climatic Change, Vol. 38, No. 4, April, pp. 447-472.
ABSTRACT: Three distinct models from earlier work are combined to: (1) produce probabilistically weighted scenarios of greenhouse-gas-induced sea-level rise; (2) support estimates of the expected discounted value of the cost of sea-level rise to the developed coastline of the United States, and (3) develop reduced-form estimates of the functional relationship between those costs to anticipated sea-level rise, the cost of protection, and the anticipated rate of property-value appreciation. Four alternative representations of future sulfate emissions, each tied consistently to the forces that drive the initial trajectories of the greenhouse gases, are considered. Sea-level rise has a nonlinear effect on expected cost in all cases, but the estimated sensitivity falls short of being quadratic. The mean estimate for the expected discounted cost across the United States is approximately $2 billion (with a 3% real discount rate), but the range of uncertainty around that estimate is enormous; indeed, the 10th and 90th percentile estimates run from less than $0.2 billion up to more than $4.6 billion. In addition, the mean estimate is very sensitive to associated sulfate emissions; it is, specifically, diminished by nearly 25% when base-case sulfate emission trajectories are considered and by more than 55% when high-sulfate trajectories are allowed.

Ecosystems and Species

Mohseni, Omid, Heinz G. Stefan, and John G. Eaton. 2003. "Global Warming and Potential Changes in Fish Habitat in U.S. Streams," Climatic Change, Vol. 59, No 3, August, pp. 389-409.
ABSTRACT: To project potential habitat changes of 57 fish species under global warming, their suitable thermal habitat at 764 stream gaging stations in the contiguous United States was studied. Global warming was specified by air temperature increases projected by the Canadian Centre of Climate Modelling General Circulation Model for a doubling of atmospheric CO2. The aquatic thermal regime at each gaging station was related to air temperature using a nonlinear stream temperature/air temperature relationship. Suitable fish thermal habitat was assumed to be constrained by both maximum temperature and minimum temperature tolerances. For cold water fishes with a 0 °C lower temperature constraint, the number of stations with suitable thermal habitat under a 2×CO2 climate scenario is projected to decrease by 36%, and for cool water fishes by 15%. These changes are associated with a northward shift of the range. For warm water fishes with a 2 °C lower temperature constraint, the potential number of stations with suitable thermal habitat is projected to increase by 31%.

Wang, Guiming, N. Thompson Hobbs, Francis J. Singer, et al. 2001. "Impacts of Climate Changes on Elk Population Dynamics in Rocky Mountain National Park, Colorado, U.S.A.," Climatic Change, Vol. 54, No. 1-2, July, pp. 205-223.
ABSTRACT: Changing climate may impact wildlife populations in national parks and conservation areas. We used logistic and non-linear matrix population models and 35 years of historic weather and population data to investigate the effects of climate on the population dynamics of elk in Rocky Mountain National Park (RMNP), Colorado, U.S.A. We then used climate scenarios derived from Hadley and Canadian Climate Center (CCC) global climate models to project the potential impact of future climate on the elk population. All models revealed density-dependent effects of population size on growth rates. The best approximating logistic population model suggested that high levels of summer precipitation accelerated elk population growth, but higher summer minimum temperatures slowed growth. The best approximating non-linear matrix model indicated that high mean winter minimum temperatures enhanced recruitment of juveniles, while high summer precipitation enhanced the survival of calves. Warmer winters and wetter summers predicted by the Hadley Model could increase the equilibrium population size of elk by about 100%. Warmer winters and drier summers predicted by the CCC Model could raise the equilibrium population size of elk by about 50%. Managers of national parks have relied on effects of weather, particularly severe winters, to regulate populations of native ungulates and prevent harmful effects of overabundance. Our results suggest that these regulating effects of severe winter weather may weaken if climate changes occur as those that are widely predicted in most climate change scenarios.

Fang, Xing, and Heinz G. Stefan. 1999. "Projections of Climate Change Effects on Water Temperature Characteristics of Small Lakes in the Contiguous U.S.," Climatic Change, Vol. 42, No. 2, June, pp. 377-412.
ABSTRACT: To simulate effects of projected climate change on water temperature characteristics of small lakes in the contiguous U.S., a deterministic, one-dimensional year-round water temperature model is applied. In cold regions the model simulates ice and snow cover on a lake. The lake parameters required as model input are surface area, maximum depth, and Secchi depth as a measure of radiation attenuation and trophic state. The model is driven by daily weather data. Weather records from 209 stations in the contiguous U.S. for the period 1961-1979 were used to represent present climate conditions. The projected climate change owing to a doubling of atmospheric CO2 was obtained from the output of the Canadian Climate Center General Circulation Model. The simulated water temperature and ice characteristics are related to the geometric and trophic state lake characteristics and to geographic location. By interpolation, the sensitivity of lake water temperature characteristics to latitude, longitude, lake geometry and trophic status can therefore be quantified for small lakes in the contiguous U.S. The 2× CO2 climate scenario is projected to increase maximum and minimum lake surface temperatures by up to 5.2°C. (Maximum surface water temperatures in lakes near the northern and the southern border of the contiguous U.S. currently differ by up to 13°C.) Maximum temperature differences between lake surface and lake bottom are projected to increase in average by only 1 to 2°C after climate warming. The duration of seasonal summer stratification is projected to be up to 66 days longer under a 2×CO2 climate scenario. Water temperatures of less than 8°C are projected to occur on lake bottoms during a period which is on the order of 50 days shorter under a 2×CO2 climate scenario. With water temperature change projected to be as high as 5.2°C, ecological impacts such as shifts in species distributions and in fish habitat are most likely. Ice covers on lakes of northern regions would also be changed strongly

Mortsch, Linda D. 1998. "Assessing the Impact of Climate Change on the Great Lakes Shoreline Wetlands," Climatic Change, Vol. 40, No. 2, October, pp. 391-416.
ABSTRACT: Great Lakes shoreline wetlands are adapted to a variable water supply. They require the disturbance of water level fluctuations to maintain their productivity. However, the magnitude and rate of climate change could alter the hydrology of the Great Lakes and affect wetland ecosystems. Wetlands would have to adjust to a new pattern of water level fluctuations; the timing, duration, and range of these fluctuations are critical to the wetland ecosystem response. Two "what if" scenarios: (1) an increased frequency and duration of low water levels and (2) a changed temporal distribution and amplitude of seasonal water levels were developed to assess the sensitivity of shoreline wetlands to climate change. Wetland functions and values such as wildlife, waterfowl and fish habitat, water quality, areal extent, and vegetation diversity are affected by these scenarios. Key wetlands are at risk, particularly those that are impeded from adapting to the new water level conditions by man-made structures or geomorphic conditions. Wetland remediation, protection and enhancement policies and programs must consider climate change as an additional stressor of wetlands.

Human Health

Gubler, Duane J., Paul Reiter, Kristie L. Ebi, Wendy Yap, Roger Nasci, and Jonathan A. Patz. 2001. "Climate Variability and Change in the United States: Potential Impacts on Vector- and Rodent-Borne Diseases," Environmental Health Perspectives, Vol. 109, Suppl 2, May, pp. 223-233.
PDF: http://ehpnet1.niehs.nih.gov/docs/2001/suppl-2/223-233gubler/gubler.pdf
ABSTRACT: Diseases such as plague, typhus, malaria, yellow fever, and dengue fever, transmitted between humans by blood-feeding arthropods, were once common in the United States. Many of these diseases are no longer present, mainly because of changes in land use, agricultural methods, residential patterns, human behavior, and vector control. However, diseases that may be transmitted to humans from wild birds or mammals (zoonoses) continue to circulate in nature in many parts of the country. Most vector-borne diseases exhibit a distinct seasonal pattern, which clearly suggests that they are weather sensitive. Rainfall, temperature, and other weather variables affect in many ways both the vectors and the pathogens they transmit. For example, high temperatures can increase or reduce survival rate, depending on the vector, its behavior, ecology, and many other factors. Thus, the probability of transmission may or may not be increased by higher temperatures. The tremendous growth in international travel increases the risk of importation of vector-borne diseases, some of which can be transmitted locally under suitable circumstances at the right time of the year. But demographic and sociologic factors also play a critical role in determining disease incidence, and it is unlikely that these diseases will cause major epidemics in the United States if the public health infrastructure is maintained and improved.

Water Resources

Frei, A., R. L. Armstrong, M. P. Clark, and M. C. Serreze. 2002. "Catskill Mountain Water Resources: Vulnerability, Hydroclimatology, and Climate-Change Sensitivity," Annals of the Association of American Geographers, Vol. 92, No. 2, June, pp. 203-224.
ABSTRACT: We present an initial assessment of the potential impact of climate change on water supply in the Metropolitan East Coast (MEC) region of the U.S. National Assessment of the Potential Consequences of Climate Variability and Change. A version of the Thornthwaite water-balance model is applied to one of six basins in the Catskill Mountains that together provide water for approximately 10 million people in New York City and other municipalities. In addition to Thornthwaite's original soil moisture reservoir, the model includes the snow pack water reservoir of Willmott, Rowe, and Mintz (1985), a ground-water storage term, and several additional modifications. Following a review of the vulnerability of water supplies and historical hydroclimatology of this region, we estimate (1) the sensitivity of water supply to altered temperature and precipitation regimes and (2) the potential impacts of specific climate-change scenarios used by national and regional climate-change assessments. The sensitivity of runoff to temperature changes is approximately 6 percent per degree C; its sensitivity to precipitation changes is approximately 1.5 - 2 percent per percent change in precipitation, for annual mean values. Under all scenarios, rising temperatures will lead to significantly diminished water supplies unless precipitation increases dramatically. Due to disagreement between precipitation projections from different models and scenarios, projected changes in mean annual water supply range from approximately +10 percent to -30 percent by the 2080s. Under the driest scenario, water supplies under mean climatic conditions will be comparable to the worst extended drought period of the twentieth century in this region. Equally important are the likely effects on the annual cycle, which include an earlier peak runoff and a reduction of the snowpack by at least 50 percent. Considered in the context of likely increased demands, these changes may be significant.

Dennis P. Lettenmaier, Andrew W. Wood, Richard N. Palmer, Eric F. Wood, and Eugene Z. Stakhiv. 1999. "Water Resources Implications of Global Warming: A U.S. Regional Perspective," Climatic Change, Vol. 43, No. 3, November, pp. 537-579.
ABSTRACT: The implications of global warming for the performance of six U.S. water resource systems are evaluated. The six case study sites represent a range of geographic and hydrologic, as well as institutional and social settings. Large, multi-reservoir systems (Columbia River, Missouri River, Apalachicola-Chatahoochee-Flint (ACF) Rivers), small, one or two reservoir systems (Tacoma and Boston) and medium size systems (Savannah River) are represented. The river basins range from mountainous to low relief and semi-humid to semi-arid, and the system operational purposes range from predominantly municipal to broadly multi-purpose. The studies inferred, using a chain of climate downscaling, hydrologic and water resources systems models, the sensitivity of six water resources systems to changes in precipitation, temperature and solar radiation. The climate change scenarios used in this study are based on results from transient climate change experiments performed with coupled ocean-atmosphere General Circulation Models (GCMs) for the 1995 Intergovernmental Panel on Climate Change (IPCC) assessment. An earlier doubled-CO2 scenario from one of the GCMs was also used in the evaluation. The GCM scenarios were transferred to the local level using a simple downscaling approach that scales local weather variables by fixed monthly ratios (for precipitation) and fixed monthly shifts (for temperature). For those river basins where snow plays an important role in the current climate hydrology (Tacoma, Columbia, Missouri and, to a lesser extent, Boston) changes in temperature result in important changes in seasonal streamflow hydrographs. In these systems, spring snowmelt peaks are reduced and winter flows increase, on average. Changes in precipitation are generally reflected in the annual total runoff volumes more than in the seasonal shape of the hydrographs. In the Savannah and ACF systems, where snow plays a minor hydrological role, changes in hydrological response are linked more directly to temperature and precipitation changes. Effects on system performance varied from system to system, from GCM to GCM, and for each system operating objective (such as hydropower production, municipal and industrial supply, flood control, recreation, navigation and instream flow protection). Effects were generally smaller for the transient scenarios than for the doubled CO2 scenario. In terms of streamflow, one of the transient scenarios tended to have increases at most sites, while another tended to have decreases at most sites. The third showed no general consistency over the six sites. Generally, the water resource system performance effects were determined by the hydrologic changes and the amount of buffering provided by the system's storage capacity. The effects of demand growth and other plausible future operational considerations were evaluated as well. For most sites, the effects of these non-climatic effects on future system performance would about equal or exceed the effects of climate change over system planning horizons.

Rosenberg, Norman J., Daniel J. Epstein, David Wang, et al. 1999. "Possible Impacts of Global Warming on the Hydrology of the Ogallala Aquifer Region," Climatic Change, Vol. 42, No. 4, August, pp. 677-692.
ABSTRACT: The Ogallala or High Plains aquifer provides water for about 20% of the irrigated land in the United States. About 20 km3 (16.6 million acre-feet) of water are withdrawn annually from this aquifer. In general, recharge has not compensated for withdrawals since major irrigation development began in this region in the 1940s. The mining of the Ogallala has been pictured as an analogue to climate change in that many GCMs predict a warmer and drier future for this region. In this paper we attempt to anticipate the possible impacts of climate change on the sustainability of the aquifer as a source of water for irrigation and other purposes in the region. We have applied HUMUS, the Hydrologic Unit Model of the U.S. to the Missouri and Arkansas-White-Red water resource regions that overlie the Ogallala. We have imposed three general circulation model (GISS, UKTR and BMRC) projections of future climate change on this region and simulated the changes that may be induced in water yields (runoff plus lateral flow) and ground water recharge. Each GCM was applied to HUMUS at three levels of global mean temperature (GMT) to represent increasing severity of climate change (a surrogate for time). HUMUS was also run at three levels of atmospheric CO2 concentration (hereafter denoted by [CO2]) in order to estimate the impacts of direct CO2 effects on photosynthesis and evapotranspiration. Since the UKTR and GISS GCMs project increased precipitation in the Missouri basin, water yields increase there. The BMRC GCM predicts sharply decreased precipitation and, hence, reduced water yields. Precipitation reductions are even greater in the Arkansas basin under BMRC as are the consequent water yield losses. GISS and UKTR climates lead to only moderate yield losses in the Arkansas. CO2-fertilization reverses these losses and yields increase slightly. CO2 fertilization increases recharge in the base (no climate change) case in both basins. Recharge is reduced under all three GCMs and severities of climate change.

Sub-National Studies

Statewide Studies

Florida

Box, Elgene O., David W. Crumpacker, and E. Dennis Hardin. 1990. "Predicted Effects of Climatic Change on Distribution of Ecologically Important Native Tree and Shrub Species in Florida," Climatic Change, Vol. 41, No. 2, February, pp. 213-248.
ABSTRACT: A previously developed plant species-climatic envelope model was evaluated further and used to predict effects of hypothesized climatic change on the potential distribution of 124 native woody plant species in Florida, U.S.A. Twelve scenarios were investigated. These included mean annual temperature increases of 1 °C or 2 °C, achieved either by equal 1 °C or 2 °C increases on a monthly basis throughout the year, or by disproportionately larger seasonal increases in winter and smaller ones in summer. The various temperature increases were then combined with each of several precipitation changes, ranging from +10% to -20%, to produce the final set of scenarios. More detailed analysis involving six of the scenarios and a subset of 28 representative, ecologically important species suggested that (1) large decreases in the Florida range of many temperate species would result if 1 °C warming occurs predominantly in winter or with a 20% decrease in annual precipitation, or (2) if 2 °C warming occurs, with or without decrease in annual precipitation, and regardless of whether there is a uniform monthly warming pattern or one that is higher in winter than in summer. Available information concerning other factors that might also affect climatic-change responses suggests that these large predicted impacts on temperate Florida species may be underestimates. Subtropical Florida species will tend to move north and inland with warming but extensive human assistance may be needed, if they are to realize their newly expanded, potential natural ranges.