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Minimizing the future impacts of climate change requires reducing the greenhouse gas (GHG) load in the atmosphere. Anthropogenic emissions include many types of GHG’s as well as particulates such as black carbon and sulfate aerosols, each of which has a different effect on the atmosphere, and a different atmospheric lifetime. Several recent studies have advocated for the importance of short timescales when comparing the climate impact of different climate pollutants, placing a high relative value on short-lived pollutants, such as methane (CH4) and black carbon (BC) versus carbon dioxide (CO2). These studies have generated confusion over how to value changes in temperature that occur over short versus long timescales. We show the temperature changes that result from exchanging CO2 for CH4 using a variety of commonly suggested metrics to illustrate the trade-offs involved in potential carbon trading mechanisms that place a high value on CH4 emissions. Reducing CH4 emissions today would lead to a climate cooling of approximately ~0.5 °C, but this value will not change greatly if we delay reducing CH4 emissions by years or decades. This is not true for CO2, for which the climate is influenced by cumulative emissions. Any delay in reducing CO2 emissions is likely to lead to higher cumulative emissions, and more warming. The exact warming resulting from this delay depends on the trajectory of future CO2 emissions but using one business-as usual-projection we estimate an increase of 3/4 °C for every 15-year delay in CO2 mitigation. Overvaluing the influence of CH4 emissions on climate could easily result in our “locking” the earth into a warmer temperature trajectory, one that is temporarily masked by the short-term cooling effects of the CH4 reductions, but then persists for many generations. 相似文献
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Permeameter data verify new turbulence process for MODFLOW 总被引：3，自引：0，他引：3
A sample of Key Largo Limestone from southern Florida exhibited turbulent flow behavior along three orthogonal axes as reported in recently published permeameter experiments. The limestone sample was a cube measuring 0.2 m on edge. The published nonlinear relation between hydraulic gradient and discharge was simulated using the turbulent flow approximation applied in the Conduit Flow Process (CFP) for MODFLOW-2005 mode 2, CFPM2. The good agreement between the experimental data and the simulated results verifies the utility of the approach used to simulate the effects of turbulent flow on head distributions and flux in the CFPM2 module of MODFLOW-2005. 相似文献
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Cesare Emiliani Eric B. Kraus Eugene M. Shoemaker 《Earth and Planetary Science Letters》1981,55(3):317-334
A paleoecological analysis of the fossil record before and after the Cretaceous/Tertiary boundary indicates that the widespread extinctions and biological stresses around the boundary are best explained in terms of a sudden, significant, but short temperature rise. L. Alvarez and co-authors, having found an enrichment in iridium at the same boundary, postulated that it was associated with the impact of an extraterrestrial body. If this body struck the ocean, the water injected into the atmosphere may have led to a transient increase in the global surface temperature. This temperature pulse may have been primarily responsible for the effects observed in the biosphere. The pattern of extinction of higher plant species suggests that splash down occurred in the northern Pacific-Bering Sea area. 相似文献
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E. M. Shoemaker F. A. Macdonald C. S. Shoemaker 《Australian Journal of Earth Sciences》2013,60(4-5):529-544
Here we present detailed geological maps and cross-sections of Liverpool, Wolfe Creek, Boxhole, Veevers and Dalgaranga craters. Liverpool crater and Wolfe Creek Meteorite Crater are classic bowl-shaped, Barringer-type craters. Liverpool was likely formed during the Neoproterozoic and was filled and covered with sediments soon thereafter. In the Cenozoic, this cover was exhumed exposing the crater's brecciated wall rocks. Wolfe Creek Meteorite Crater displays many striking features, including well-bedded ejecta units, crater-floor faults and sinkholes, a ringed aeromagnetic anomaly, rim-skirting dunes, and numerous iron-rich shale balls. Boxhole Meteorite Crater, Veevers Meteorite Crater and Dalgaranga crater are smaller, Odessa-type craters without fully developed, steep, overturned rims. Boxhole and Dalgaranga craters are developed in highly foliated Precambrian basement rocks with a veneer of Holocene colluvium. The pre-existing structure at these two sites complicates structural analyses of the craters, and may have influenced target deformation during impact. Veevers Meteorite Crater is formed in Cenozoic laterites, and is one of the best-preserved impact craters on Earth. The craters discussed herein were formed in different target materials, ranging from crystalline rocks to loosely consolidated sediments, containing evidence that the impactors struck at an array of angles and velocities. This facilitates a comparative study of the influence of these factors on the structural and topographic form of small impact craters. 相似文献
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Chi Zhang Christine A. Shoemaker Joshua D. Woodbury Mingliang Cao Xueping Zhu 《水文研究》2013,27(17):2509-2523
The obvious decline in stream flow to the Biliu River reservoir over the period 1990–2005 has raised increasing concerns. Climate change and human activities, which mainly include land use changes, hydraulic constructions and artificial water consumption, are considered to be the most likely reasons for the decline in stream flow. This study centres on a detailed analysis of the runoff response to changes in human activities. Using a distributed hydrological model, (Soil and Water Assessment Tool), we simulated runoffs under different human activity and climate scenarios to understand how each scenario impacts stream flow. The results show that artificial water consumption correlates with the precipitation (wet, normal and dry) of the year in question and is responsible for most of the decrease in runoff during each period and for each different wetness year. A Fuzzy Inference Model is also used to find the relationship between the precipitation and artificial water consumption for different years, as well as to make inferences regarding the future average impact on runoff. Land use changes in the past have increased the runoff by only a small amount, while another middle reservoir (Yunshi) has been responsible for a decrease in runoff since operation began in 2001. We generalized the characteristics of the human activities to predict future runoff using climate change scenarios. The future annual flow will increase by approximately 10% from 2011 to 2030 under normal human activities and future climate change scenarios, as indicated by climate scenarios with a particularly wet year in the next 20 years. This study could serve as a framework to analyse and predict the potential impacts of changes both in the climate and human activities on runoff, which can be used to inform the decision making on the river basin planning and management. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Adel Shirmohammadi William L. Magette Leslie L. Shoemaker 《Ground Water Monitoring & Remediation》1991,11(1):112-118
Non-point source pollution of ground water systems has become a national concern in recent years. Researchers and regulatory agencies are investigating the source and processes of the contamination. Agricultural best management practices (BMPs) traditionally developed to reduce non-point source pollution of surface water resources are being investigated for their impact on ground water quality. This study used the CREAMS model to simulate the long-term effects of seven different BMPs on nitrate nitrogen (NO3 -N) loadings to a shallow, unconfined ground water system. Two representative watersheds, 5.8 and 8.9 hectares (14.3 and 22 acres) in area, in the Coastal Plain physiographic region of Maryland were selected for study. Soils in these watersheds belong to the Matapeake silt loam series and have moderate infiltration capacity. Results from this study indicated that BMPs used in conjunction with winter cover (barley) reduced NO3 -N leaching to the ground water system. It was also found that turfgrass reduced surface losses of water and nitrogen, but increased leaching losses of water and NO3 -N significantly. All of the BMPs simulated in this study resulted in leachate NO3 -N concentrations exceeding 10 ppm, the U.S. EPA health standard for public drinking water, indicating a need for alternate practices for reducing nitrate leaching. 相似文献