Quantitative simulations of the global-scale benefits of climate change mitigation are presented, using a harmonised, self-consistent approach based on a single set of climate change scenarios. The approach draws on a synthesis of output from both physically-based and economics-based models, and incorporates uncertainty analyses. Previous studies have projected global and regional climate change and its impacts over the 21st century but have generally focused on analysis of business-as-usual scenarios, with no explicit mitigation policy included. This study finds that both the economics-based and physically-based models indicate that early, stringent mitigation would avoid a large proportion of the impacts of climate change projected for the 2080s. However, it also shows that not all the impacts can now be avoided, so that adaptation would also therefore be needed to avoid some of the potential damage. Delay in mitigation substantially reduces the percentage of impacts that can be avoided, providing strong new quantitative evidence for the need for stringent and prompt global mitigation action on greenhouse gas emissions, combined with effective adaptation, if large, widespread climate change impacts are to be avoided. Energy technology models suggest that such stringent and prompt mitigation action is technologically feasible, although the estimated costs vary depending on the specific modelling approach and assumptions. 相似文献
We have determined the dry weight of suspended particulate matter in seawater in a section through the western Atlantic Ocean from 75°N to 52°S. The concentrations, operationally defined as that weight retained on 0.6-μm and 0.4-μm pore size Nuclepore filters, contained in 1 kg of seawater, range from 5 to 300 μg/kg and show readily explainable regional features. High concentrations are found in surface waters and in association with radpidly moving bottom waters in the Denmark Straits overflow and in Antarctic bottom waters to 15°S. Low concentrations, <12 μg/kg, characterize the mid-water regions of the sub-tropical gyres. High concentrations are seen in sinking Labrador Sea water and in a plume extending at least a kilometer off the bottom at 35°N–40°N where the cruise track intersects the North Atlantic gyre. It is doubtful whether this important phenomenon could be observed by any means other than through particulate observations, either optical or gravimetric, and this provides a unique insight into the scale of vertical turbulent processes. 相似文献
An understanding of the evolution of cracks in concrete structures due to long term natural deformation is important to civil engineers, but quantitative measurements can be difficult to make. However, digital imaging offers a potential solution. This short paper illustrates the operational application of automated image processing techniques for accurate, multi-temporal crack measurements. The first part of this paper provides an overview of automatic feature extraction, essential for automatic crack detection. The latter part describes the methods developed for detecting and measuring cracks. Due to the long term nature of the application, operational results have yet to be finalised, although sample results are presented 相似文献
Phenotypic variation within species can have community- and ecosystem-level effects. Such variation may be particularly important in ecosystem engineers, including many invasive species, because of the strong influence of these species on their surrounding communities and environment. We combined field surveys and glasshouse experiments to investigate phenotypic variation within the invasive common reed, Phragmites australis, among four estuarine source sites along the east coast of North America. Field surveys revealed variation in P. australis height and stem density among source sites. In a glasshouse environment, percent germination of P. australis seeds also varied across source sites. To test the degree to which phenotypic variation in P. australis reflected genetic or environmental differences, we conducted a glasshouse common garden experiment assessing the performance of P. australis seedlings from the four source sites across a salinity gradient. Populations maintained differences in morphology and growth in a common glasshouse environment, indicating a genetic component to the observed phenotypic variation. Despite this variation, experimentally increased porewater salinity consistently reduced P. australis stem density, height, and biomass. Differences in these morphological metrics are important because they are correlated with the impacts of invasive P. australis on the ecological communities it invades. Our results indicate that both colonization and spread of invasive P. australis will be dependent on the environmental and genetic context. Additional research on intraspecific variation in invasive species, particularly ecosystem engineers, will improve assessments of invasion impacts and guide management decisions in estuarine ecosystems. 相似文献
In order to simulate undrained conditions using the discrete element method, a constant sample volume is often assumed. There are well-recognised problems with these constant-volume triaxial simulations, particularly of dense samples, which inhibit quantitative comparison with laboratory experiments. In this paper, four possible explanations for these problems with conventional constant-volume simulations of ideal spherical particles are explored, each of which has a physical basis: particle crushing, the presence of highly compressible air within the sample, or the reduction in stiffness due to particle surface asperities or non-spherical particle shapes. These options are explored independently and in combination through implementation in the open-source LAMMPS code. In situations where a significant amount of particle crushing occurs, it is important to incorporate this in the simulations so that stresses are not over-estimated. There is experimental evidence that irregular particles have lower Young’s moduli than the Hertzian spheres often used in DEM. In the absence of particle crushing, the most effective method to achieve more realistic stress–strain responses is to reduce the particle shear modulus substantially. This approach has the added computational benefit of enabling an increase in the simulation time-step.