Technical summary

Human interference with the climate system is occurring. Climate change poses risks for human and natural systems. The assessment of impacts, adaptation, and vulnerability in the Working Group II contribution to the IPCC's Fifth Assessment Report (WGII AR5) evaluates how patterns of risks and potential benefits are shifting due to climate change and how risks can be reduced through mitigation and adaptation. It recognizes that risks of climate change will vary across regions and populations, through space and time, dependent on myriad factors including the extent of mitigation and adaptation

Potential Production and Environmental Effects of Switchgrass and Traditional Crops under Current and Greenhouse-Altered Climate in the Central United States: A Simulation Study

If, as many climate change analysts _ speculate, industrial and other emissions of CO2 can be offset by substitution of biofuels, large areas of land, including agricultural land, may be converted to the production of biomass feedstocks. This paper explores the feasibility for the Missouri–Iowa–Nebraska–Kansas (MINK) region of the US of converting some agricultural land to the production of switchgrass (Panicum virgatum L.), a perennial warm season grass, as a biomass energy crop. The erosion productivity impact calculator (EPIC) crop growth model simulated production of corn (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), soybean (Glycine max L.), winter wheat (Triticum aestivum L.) and switchgrass at 302 sites within the MINK region. The analysis is done for both current climatic conditions and a regional climate model-based scenario of possible climate change. Daily climate records from 1983 to 1993 served as baseline and the NCAR-RegCM2 model (RegCM hereafter) nested within the CSIRO general circulation model (GCM) provided the climate change scenario. Crop production was simulated at two atmospheric CO2 concentrations ([CO2]) at 365 and 560 ppm to consider the CO2-fertilization effect. Simulated yields of the perennial switchgrass increased at all sites with a mean yield increase of 5.0 Mg ha-1 under the RegCM climate change scenario. Switchgrass yields benefited from temperature increases of 3.0–8.0°C, which extended the growing season and reduced the incidence of cold stress. Conversely, the higher temperatures under the RegCM scenario decreased yields of corn, soybean, sorghum and winter wheat due to increased heat stress and a speeding of crop maturity. With no CO2-fertilization effect, EPIC simulated maximum decreases from baseline of 1.5 Mg ha-1 for corn, 1.0 Mg ha-1 for sorghum, 0.8 Mg ha−1 for soybean and 0.5 Mg ha-1 for winter wheat. Simulated yields increased for all crops under the RegCM scenario with CO2 set to 560 ppm. Yields increased above baseline for 34% of the soybean and 37% of the winter wheat farms under RegCM/[CO2]=560 ppm scenario. Water use increased for all crops under the higher temperatures of the CSIRO scenario. Precipitation increases resulted in greater runoff from the traditional crops but not from switchgrass due to the crop’s increased growth and longer growing season. Simulated soil erosion rates under switchgrass and wheat cultivation were less severe than under corn management. However, simulated erosion under switchgrass was considerable in eastern Iowa during the period of crop establishment because of strong winds at that time

The Uncertainty due to Spatial Scale of Climate Scenarios in Integrated Assessments: An Example from U.S. Agriculture

We investigate the effects of different climate scenario resolutions on estimates of the impacts of future climate change on agriculture in the United States. Climate scenarios were developed using both a coarse resolution, global scale general circulation model and a spatially more refined regional climate model, nested within the coarse model. The scenarios are similar on a very broad regional scale, but show important differences on a subregional scale. In most areas the fine scale scenario produces a more severe climate change. Simulated changes in crop yields (e.g., cotton, soybean, corn, wheat) were constructed under both the coarse and fine scale scenarios for the conterminous United States. The results demonstrate that the spatial scale of climate scenarios affects the estimates of regional changes in crop yields on several levels of spatial aggregation and the economic impact on the agricultural sector as a whole. For the elevated CO2 case, national economic welfare increased under the coarse scale climate scenario, but remained virtually unchanged under the fine scale scenario. With adaptations, both scenarios showed substantial increases, but these were still considerably larger for the coarse scale scenario. Regional indicators of economic activity were of opposite sign in some regions, based on the scenario scale for both cases. Such differences in economic magnitudes or signs become important in public policy debates concerning climate change. Hence refinement of spatial scale of scenarios should be carefully considered in future regional integrated assessments

The sensitivity of California water resources to climate change scenarios

Using the latest available General Circulation Model (GCM) results we present an assessment of climate change impacts on California hydrology and water resources. The approach considers the output of two GCMs, the PCM and the HadCM3, run under two different greenhouse gas (GHG) emission scenarios: the high emission A1fi and the low emission B1. The GCM output was statistically downscaled and used in the Variable Infiltration Capacity (VIC) macroscale distributed hydrologic model to derive inflows to major reservoirs in the California Central Valley. Historical inflows used as inputs to the water resources model CalSim II were modified to represent the climate change perturbed conditions for water supply deliveries, reliability, reservoir storage and changes to variables of environmental concern. Our results show greater negative impacts to California hydrology and water resources than previous assessments of climate change impacts in the region. These impacts, which translate into smaller streamflows, lower reservoir storage and decreased water supply deliveries and reliability, will be especially pronounced later in the 21st Century and south of the San Francisco bay Delta. The importance of considering how climate change impacts vary for different temporal, spatial, and institutional conditions in addition to the average impacts is also demonstrated