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101.
Numerous policy options exist to reduce future greenhouse gas emissions. A single-basket approach, which controls aggregate emissions, was adopted by the Kyoto Protocol. Such an approach allows emissions reductions of one gas to be traded with those of other gases in the “basket”, with the trade “price” determined by some weighting metric like the Global Warming Potential. To reduce stratospheric ozone depletion, the Montreal Protocol also dealt with controlling many compounds, but did so employing an alternative, multi-basket scheme. Trading was allowed within each basket, but not among baskets. While the Montreal Protocol has been highly successful using this approach, we show that if a single-basket approach had been adopted the short-term success could have been at risk due to the non-unique relationship between controls and environmental impacts when using a single basket. Using climate policy as an example, and without considering technological and economic constraints, we further show that the magnitude of the ambiguities in impacts associated with a single-basket approach depends on the rapidity of the emission phaseout. Fast phaseouts lead to less ambiguity than do slow ones. These results suggest that for each set of greenhouse gas control policies considered, the benefit of additional flexibility associated with a single-basket approach should be weighed against the associated increased uncertainties in the impacts to ascertain whether a single- or a multi-basket approach has the greater chance of successfully mitigating climate change.  相似文献   
102.
Stable isotopes (δ18O, δ2H), tritium (3H), and helium isotopes (3He, 4He) were used for evaluating groundwater recharge sources, flow paths, and residence times of three watersheds in the Cape Verde Islands (West Africa). Stable isotopes indicate the predominance of high-elevation precipitation that undergoes little evaporation prior to groundwater recharge. In contrast to other active oceanic hotspots, environmental tracers show that deep geothermal circulation does not strongly affect groundwater. Low tritium concentrations at seven groundwater sites indicate groundwater residence times of more than 50 years. Higher tritium values at other sites suggest some recent recharge. High 4He and 3He/4He ratios precluded 3H/3He dating at six sites. These high 3He/4He ratios (R/Ra values of up to 8.3) are consistent with reported mantle derived helium of oceanic island basalts in Cape Verde and provided end-member constraints for improved dating at seven other locations. Tritium and 3H/3He dating shows that São Nicolau Island’s Ribeira Fajã Basin has groundwater residence times of more than 50 years, whereas Fogo Island’s Mosteiros Basin and Santo Antão Island’s Ribeira Paul Basin contain a mixture of young and old groundwater. Young ages at selected sites within these two basins indicate local recharge and potential groundwater susceptibility to surface contamination and/or salt-water intrusion.  相似文献   
103.
Insight into the causes of the annual and semi-annual ozone oscillations may be gained from the analysis of photochemical model behavior. In this paper, the monthly variations of the ozone mixing ratio computed by the two-dimensional photochemical model of Garcia and Solomon (1983, J. geophys. Res. 88, 1379) are Fourier-analyzed and compared with SBUV observations of ozone mixing ratio. Remarkably good qualitative agreement between the model calculations and the observations is found. Analysis of computed transport and chemical production and destruction rates reveals the causes of the modelled seasonal ozone variations.

It will be shown that at high latitudes and low altitudes, modelled ozone abundances increase in the winter due to transport and decrease in the summer due to chemical destruction. In the middle stratosphere, the calculated annual ozone variation is largely due to the annual variation in the odd-oxygen production rate, and in the upper stratosphere, the computed annual ozone variation is caused by the large calculated annual oscillation in temperature. Comparison between the model and observations suggests that the equatorial semi-annual oscillation above 10 mb is caused mainly by the semi-annual temperature and wind oscillation (SAO). Below 10 mb the computed equatorial ozone variation is caused by the increased rates of odd-oxygen production associated with the semi-annual zenith crossings of the Sun. Finally, the calculated polar semi-annual ozone oscillations are found to be caused by modulation of the radiatively driven middle-stratospheric ozone variation by temperature dependent chemical destruction processes.  相似文献   

104.
105.
Determinants of foreign exploration and development spending by US oil companies are examined with multiple regression analysis. Since major US oil companies earn higher profits abroad, I test the role of profit rate surrogates and cash flow in a petroleum investment model. A high income tax rate is shown to discourage foreign oil investment, a finding that should be recognized by foreign governments. Institutional factors also appear to limit the flow of investment funds out of the United States, despite attractive foreign profit rates.  相似文献   
106.
Measurements of dissolved gases have numerous applications in ground water hydrology, and it is now possible to measure the total dissolved gas pressure in situ using a probe. Dissolved gas pressure is measured by submerging a headspace volume with a gas-permeable membrane, allowing dissolved gases in the water to equilibrate with gases in the headspace, then measuring the pressure in the headspace with a pressure transducer. Total dissolved gas pressure (TGP) probes have many potential uses in ground water studies employing dissolved gases, including: (1) determining approximate excess air levels, which may provide information about the time and location of recharge; (2) screening wells for air contamination, which can compromise the accuracy of dissolved gas tracer techniques: (3) detecting a trapped gas phase, which can significantly reduce hydraulic conductivity and impede the transport of dissolved solutes and gases; (4) enabling the use of gas-filled passive diffusion samplers for determining accurate dissolved gas concentrations; and (5) determining relative concentrations of CH4 and CO2 when they are known to be highly abundant. Although TGP probes designed for surface water have been available for several years, TGP probes suitable for ground water applications have only recently become available. Herein we present what are, to our knowledge, the first reported ground water dissolved gas data collected using a TGP probe. We also explain the basic operating principles of these probes and discuss the potential applications listed.  相似文献   
107.
Comparing the Performance of Forest gap Models in North America   总被引:6,自引:0,他引:6  
Forest gap models have a long history in the study of forest dynamics, including predicting long-term succession patterns and assessing the potential impacts of climate change and air pollution on forest structure and composition. In most applications, existing models are adapted for the specific question at hand and little effort is devoted to evaluating alternative formulations for key processes, although this has the potential to significantly influence model behavior. In the present study, we explore the implications of alternative formulations for selected ecological processes via the comparison of several gap models. Baseline predictions of forest biomass, composition and size structure generated by several gap models are compared to each other and to measured data at boreal and temperate sites in North America. The models ForClim and LINKAGES v2.0 were compared based on simulations of a temperate forest site in Tennessee, whereas FORSKA-2V, BOREALIS and ForClim were compared at four boreal forest sites in central and eastern Canada. Results for present-day conditions were evaluated on their success in predicting forest cover, species composition, total biomass and stand density, and allocation of biomass among species. In addition, the sensitivity of each model to climatic changes was investigated using a suite of six climate change scenarios involving temperature and precipitation. In the temperate forest simulations, both ForClim and LINKAGES v2.0 predicted mixed mesophytic forests dominated by oak species, which is expected for this region of Tennessee. The models differed in their predictions of species composition as well as with respect to the simulated rates of succession. Simulated forest dynamics under the changed climates were qualitatively similar between the two models, although aboveground biomass and species composition in ForClim was more sensitive to drought than in LINKAGES v2.0. Under a warmer climate, the modeled effects of temperature on tree growth in LINKAGES v2.0 led to the unrealistic loss of several key species. In the boreal forest simulations, ForClim predicted significant forest growth at only the most mesic site, and failed to predict a realistic species composition. In contrast, FORSKA-2V and BOREALIS were successful in simulating forest cover, general species composition, and biomass at most sites. In the climate change scenarios, ForClim was highly sensitive, whereas the other two models exhibited sensitivity only at the drier central Canadian sites. Although the studied sites differ strongly with respect to both the climatic regime and the set of dominating species, a unifying feature emerged from these simulation exercises. The major differences in model behavior were brought about by differences in the internal representations of the seasonal water balance, and they point to an important limitation in some gap model formulations for assessing climate change impacts.  相似文献   
108.
109.
The catalytic destruction of stratospheric ozone by the oxides of nitrogen is believed to be an important part of the global ozone balance. The lack of sufficient measurements of NO x concentrations has impeded efforts to quantify this process. Recent measurements of stratospheric nitrogen dioxide from ground-based stations as well as aircraft and balloons have provided a first approximation to a global distribution of NO2 vertical columns at sunset. These observed vertical columns have been translated into time-dependent vertical NO2 profiles by means of a one-dimensional atmospheric photochemical model. Using recent observations of air temperature and ozone along with this information, the independent instantaneous (one second) rates of ozone production from oxygen photolysis P(O3), of ozone destruction from pure oxygen species (Chapman reactions) L(O x ), and of ozone destruction by nitrogen oxides L(NO x ) were estimated over the three-dimensional atmosphere. These quantities are displayed as zonal average contour maps, summed over various latitude zones, summed over various altitude bands, and integrated globally between 15 and 45 km. Although the global summation between 15 and 45 km by no means tells the complete story, these numbers are of some interest, and the relative values are: P(O3), 100; L(O x ), 15; L(NO x ), 45±15. It is to be emphasized that this relative NO x contribution to the integrated ozone balance is not a measure of the sensitivity of ozone to possible perturbations of stratospheric NO x ; recent model results must be examined for current estimates of this sensitivity.  相似文献   
110.
Formation,history and energetics of cores in the terrestrial planets   总被引:1,自引:0,他引:1  
The cores of the terrestrial planets Earth, Moon, Mercury, Venus and Mars differ substantially in size and in history. Though no planet other than the Earth has a conclusively demonstrated core, the probable cores in Mercury and Mars and Earth's core show a decrease in relative core size with solar distance. The Moon does not fit this sequence and Venus may not. Core formation must have been early (prior to ~4 · 109 yr. ago) in the Earth, by virtue of the existence of ancient rock units and ancient paleomagnetism and from UPb partitioning arguments, and in Mercury, because the consequences of core infall would have included extensional tectonic features which are not observed even on Mercury's oldest terrain. If a small core exists in the Moon, still an open question, completion of core formation may be placed several hundred million years after the end of heavy bombardment on tectonic and thermal grounds. Core formation time on Mars is loosely constrained, but may have been substantially later than for the other terrestrial planets. The magnitude and extent of early heating to drive global differentiation appear to have decreased with distance from the sun for at least the smaller bodies Mercury, Moon and Mars.Energy sources to maintain a molten state and to fuel convection and magnetic dynamos in the cores of the terrestrial planets include principally gravitational energy, heat of fusion, and long-lived radioactivity. The gravitational energy of core infall is quantifiable and substantial for all bodies but the Moon, but was likely spent too early in the history of most planets to prove a significant residual heat source to drive a present dynamo. The energy from inner core freezing in the Earth and in Mercury is at best marginally able to match even the conductive heat loss along an outer core adiabat. Radioactive decay in the core offers an attractive but unproven energy source to maintain core convection.  相似文献   
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