B44B-01 INVITED
Against the Grain: The Influence of Changing Agricultural Management on the Earth System
The rise of modern agriculture was one of the most transformative events in human history, and has forever changed our relationship to the natural world. By clearing tropical forests, practicing subsistence agriculture on marginal lands and intensifying industrialized farmland production, agricultural practices are changing the worldês landscapes in pervasive ways. In the past decade, we have made tremendous progress in monitoring agricultural expansion from satellites, and modeling associated environmental impacts. In the past decade, the Earth System Science research community has begun to recognize the importance of agricultural lands, particularly as they continue expanding at the expense of important natural ecosystems, potentially altering the planetês carbon cycle and climate. With the advent of new remote sensing and global modeling methods, several efforts have documented the expansion of agricultural lands, the corresponding loss of natural ecosystems, and how this may influence the earth system. But the geographic expansion of agricultural lands is not the whole story. While significant agricultural expansion (or extensification) has occurred in the past few decades, the intensification of agricultural practices Ð under the aegis of the –Green Revolution" Ð has dramatically altered the relationship between humans and environmental systems across the world. Simply put, many of the worldês existing agricultural lands are being used much more intensively as opportunities for agricultural expansion are being exhausted elsewhere. In the last 40 years, global agricultural production has more than doubled Ð although global cropland has increased by only 12% Ð mainly through the use of high yielding varieties of grain, increased reliance on irrigation, massive increases in chemical fertilization, and increased mechanization. Indeed, in the past 40 years there has been a 700% increase in global fertilizer use and a 70% increase in irrigated cropland area. While these modern agricultural practices have successfully increased food production, they have caused extensive environmental damage across the planet. Unfortunately, the current generation of remote sensing datasets and global models only considers the geographic extent of agricultural land; the actual practice of agriculture (what is grown, how it is grown, what inputs are used) is almost completely ignored. This is a serious oversight. In this presentation, I will present new efforts to document the patterns of global agricultural practices and management regimes, and new techniques for incorporating them into global ecological and climate models.
B44B-02
Conceptual Model Linking Land Use to Human Consumption in the Agriculture Sector
Human activities are profoundly influenced by weather and climate. Agriculture is the most extensive and important uses of land, and is particularly sensitive to climate variability. In this talk we will present a conceptual model that seeks to integrate human appropriation of terrestrial net primary production (HANPP) with socio- economic models to explore the influence of commodities markets on land use decisions. Focusing on a single commodity as a building block, we explore the methodological and data requirements of the model, presenting the impact of precipitation, temperature, population and land use on food prices through a carbon-based calculation of supply and demand. We demonstrate the critical importance of accurate and temporally varying land use maps for models that integrate the social and biophysical spheres and show the mechanistic sensitivity of land use to change in the supply and demand ratio.
B44B-03
Dust and the Dust Bowl: Connections between 1930's drought and dust
There have been a number of investigations into the causes and physical mechanisms of the 1930's Dust Bowl, and together they provide a reasonable explanation of the drought in terms of its length and severity. However no published investigations have considered the possible climatic effects caused by the considerable amount of airborne dust that was generated as a consequence of poor land use management in the late 19th and early 20th centuries. In order to investigate the effects of airborne dust on North American climate during the 1930's, we have performed a climate model sensitivity study that isolates the effects of dust on climate in a regional climate model. The results of the study show that an essentially permanent dust cloud existed over North America through the duration of the drought. The dust cloud, which we show was quite thick over its center in the Midwest, blocked enough solar radiation to reduce surface temperatures by about 1 K. In addition, we show that a complex feedback between dust and drought caused a spatial redistribution of precipitation, in which various regions gained or lost an average of about 1 mm/day of precipitation.
B44B-04 INVITED
Will Biofuel Expansion Mitigate Climate Change?
For biofuels to displace a substantial fraction of fossil fuel consumption, production will have to be scaled up at least an order of magnitude over current levels. The net effect of this expansion on climate will depend not only on the energy inputs and outputs of biofuel production, but also on the climate effects of land-use changes associated with the expansion. We distinguish three types of biofuel related land-cover conversions (1) food crop to biofuels, (2) forest to biofuels, and (3) marginal grassland to biofuels and discuss the potential production and net climate impact for each. We argue that the first two of these may contribute to energy supply but are unlikely to produce significant climate benefits over first 50 years of production, with only marginal lands offering a climate benefit. Using historical land-use datasets to define the current extent of marginal or degraded grasslands, and maps of native net primary production and food crop yield trends to estimate their potential yields, we estimate that ~1 Pg C per year can be attained on these lands, which would provide just 3% of current global energy needs. In addition, we discuss other societal and ecosystem impacts of biofuel expansion, and how these impacts compare to those projected for climate change itself.
B44B-05
Transitioning from Corn to Switchgrass in the US Great Plains: Implications for Climate and Water Resource
Much attention has been paid to the use of corn as a biofuel, in large part because corn is already grown throughout much of the US and technology is in place to convert it to ethanol. Increasingly, however, it is recognized that other types of vegetation are likely to be more efficient producers of biofuel. In particular, switchgrass (the primary component of prairie long grass) may be a very efficient producer in the Great Plains (as well as portions of the Midwest and Southeast), where it is an indigenous species. The dominant agricultural planting in the Great Plains at present is corn. A transition from corn to switchgrass may have numerous benefits, both because it may be a better source of biofuels, and because in the water-scarce Great Plains it would likely make better use of available water resources. In addition to these positive benefits, however, there may be effects on the climate of this region that can be deleterious. While switchgrass, with its deep and extensive root system may be less subject to drought, and less needing of irrigation, than corn, it also cycles much less water during its growing season. This reduction in water input to the atmosphere means less water available for local and regional precipitation, and also dramatically affects the surface energy balance, resulting in more sensible and longwave heating of the atmosphere. This may cause a significant increase in surface air temperature and stabilization of the atmosphere, leading to a reduction in precipitation as well as increased evaporative potential (both of which would help negate any increased water efficiency of switchgrass). We use the MM5 and WRF regional climate models to investigate these effects over the Great Plains. Simulations were made assuming all corn ('irrigated cropland') and all switchgrass ('grassland') and compared to a control using present-day land use types that is largely a mix of the two. Model runs are being made for three years with normal precipitation, plus years with precipitation above and below normal (as based on observations). The high-resolution North American Regional Reanalysis provides lateral and initial conditions for the model simulations. Preliminary results suggest that a transition from corn to switchgrass can increase daily maximum temperatures by up to 4 C, with smaller increases in daily minimums. Precipitation decreases by 15-25%. Overall, the tendency is for warmer and drier conditions. These results also suggest that effects due to global warming may be exacerbated by a large-scale change to switchgrass.
B44B-06
Is a substantial global bioenergy system feasible? A spatial analysis using a dynamic global vegetation model
Avoiding dangerous climate change requires drastic reductions in greenhouse gas emissions. However, the global demand for energy is projected to grow by more than 50 % until 2030 (IEA, 2006) and therefore actions are urgently required to decarbonize the global economy. Second generation bioenergy systems are promoted as a way forward to displace large amounts of fossil fuels with renewable materials, thereby increasing energy security and stabilizing atmospheric greenhouse gas concentrations. At the same time, concerns are being raised regarding the sustainability of large-scale dedicated biomass plantations with regard to extensive mono- cultures, irrigation and fertilization requirements. We use a dynamic global vegetation model (DGVM) including current agriculture to simulate the effects of rising competition for land when an additional spatially extensive production system for a new commodity, bioenergy, is added to the global land use mix under continued increase in global population size as well as per capita energy consumption. How much land is needed for a significant bioenergy generation if sufficient food production is warranted and what are the consequences for the terrestrial biosphere? To assess the potential impacts of a significant global bioenergy sector, we produced a selection of scenarios based on prior assumptions of total bioenergy demand, progress in conversion technologies and the availability of cultivable land limited by food requirements and biodiversity protection. We present the corresponding land use patterns as well as their impacts on the terrestrial carbon balance, evapotranspiration fluxes and irrigation demand. We find that an area of up to 50 % the size of current agricultural land is needed for the cultivation of ligno-cellulosic crops to satisfy high bioenergy demands. Carbon fluxes into the atmosphere caused by the removal of natural vegetation can equal those of 8 years of fossil fuel combustion.
B44B-07
Comparative Effects of Ethanol (E85), Gasoline, and Wind-Powered Electric Vehicles on Cancer, Mortality, Climate-Relevant Emissions, and Land requirements in the United States
In this study, a nested global-through-urban air pollution/weather forecast model is combined with high- resolution future emission inventories, population data, and health effects data to examine the effect of converting from gasoline to a high-ethanol blend (E85) on cancer, mortality, and hospitalization in the U.S. as a whole and Los Angeles in particular. The effects of both are then compared with those from converting to wind-powered battery-electric vehicles (WBEVs). Under the base-case emission scenario, which accounted for projected improvements in gasoline and E85 vehicle emission controls, complete conversion to E85, which is unlikely due to land-use constraints, was found to increase ozone-related mortality, hospitalization, and asthma by about 9 percent in Los Angeles and 4 percent in the U.S. as a whole relative to 100 percent gasoline. Ozone increases in Los Angeles and the northeast U.S. were partially offset by decreases in the southeast. E85 also increased PAN in the U.S. but was estimated to cause little change in cancer risk relative to gasoline. Both gasoline and ethanol are anticipated to cause at least 10,000-20,000 premature deaths in the U.S. in 2020, which would be eliminated upon conversion to WBEVs. WBEVs require 30 times less land area than corn ethanol and 20 times less land area than cellulosic ethanol for powering the same vehicle fleet. About 70,000-120,000 5 MW wind turbines in average wind speeds exceeding 8 m/s could power all U.S. onroad vehicles, eliminating up to 26 percent of U.S. carbon, compared with a best-case carbon reduction of 0.2 percent for corn-ethanol and 4 percent for cellulosic ethanol, based on recent lifecycle emission data and landuse constraints. In sum, both gasoline and E85 pose public health risks, with E85 causing equal or possibly more damage. The conversion to battery-electric vehicles or hydrogen fuel cell vehicles powered by wind or another clean renewable, is a significantly superior solution to ethanol or gasoline in terms of human health, climate-relevant emissions, and landuse requirements. http://www.stanford.edu/group/efmh/jacobson/E85vWindSol
B44B-08
Wind Energy and Climate: Modeling the Atmospheric Impacts of Wind Energy Turbines
The size and number of wind farms is growing across the globe. Wind energy provides the climatic benefit of producing energy without emitting CO2, however wind energy also produces unintended impacts. Large wind farms directly influence the atmospheric boundary layer by (1.) reducing wind speeds, (2.) generating blade scale turbulence in the wake of the turbines, and (3.) generating shear driven turbulence due to the reduced wind speeds in the turbine wake. Consequentially, large wind turbines can also have indirect effects on the local climate by influencing surface fluxes, advection of heat and moisture, and turbulent transport in the boundary layer. The Weather Research and Forecasting Model (WRF) was modified to include an energy conserving wind farm parameterization. The wind farm parameterization exerts an elevated drag force on the wind, converts a fraction of the resolved flow into turbulent kinetic energy, and keeps track of the energy generated by the parameterized wind turbines. This presentation will use model simulations to examine the impacts that wind farms can have on the day to day weather and local climate of a region.