Climate change impacts on global agriculture

Based on predicted changes in the magnitude and distribution of global precipitation, temperature and river flow under the IPCC SRES A1B and A2 scenarios, this study assesses the potential impacts of climate change and CO₂ fertilization on global agriculture. The analysis uses the new version of the GTAP-W model, which distinguishes between rainfed and irrigated agriculture and implements water as an explicit factor of production for irrigated agriculture. Future climate change is likely to modify regional water endowments and soil moisture. As a consequence, the distribution of harvested land will change, modifying production and international trade patterns. The results suggest that a partial analysis of the main factors through which climate change will affect agricultural productivity provide a false appreciation of the nature of changes likely to occur. Our results show that global food production, welfare and GDP fall in the two time periods and SRES scenarios. Higher food prices are expected. No matter which SRES scenario is preferred, we find that the expected losses in welfare are significant. These losses are slightly larger under the SRES A2 scenario for the 2020s and under the SRES A1B scenario for the 2050s. The results show that national welfare is influenced both by regional climate change and climate-induced changes in competitiveness.     

On the generation of climate model ensembles

Climate model ensembles are used to estimate uncertainty in future projections, typically by interpreting the ensemble distribution for a particular variable probabilistically. There are, however, different ways to produce climate model ensembles that yield different results, and therefore different probabilities for a future change in a variable. Perhaps equally importantly, there are different approaches to interpreting the ensemble distribution that lead to different conclusions. Here we use a reduced-resolution climate system model to compare three common ways to generate ensembles: initial conditions perturbation, physical parameter perturbation, and structural changes. Despite these three approaches conceptually representing very different categories of uncertainty within a modelling system, when comparing simulations to observations of surface air temperature they can be very difficult to separate. Using the twentieth century CMIP5 ensemble for comparison, we show that initial conditions ensembles, in theory representing internal variability, significantly underestimate observed variance. Structural ensembles, perhaps less surprisingly, exhibit over-dispersion in simulated variance. We argue that future climate model ensembles may need to include parameter or structural perturbation members in addition to perturbed initial conditions members to ensure that they sample uncertainty due to internal variability more completely. We note that where ensembles are over- or under-dispersive, such as for the CMIP5 ensemble, estimates of uncertainty need to be treated with care.     

Constraining Holocene lake levels and coastal dune activity in the Lake Michigan basin

Sediment cores collected from embayed lakes along the east-central coast of Lake Michigan are used to construct aeolian sand records of past coastal dune mobility, and to constrain former lake levels in the Lake Michigan basin. Time series analysis of sand cycles based on the weight-percent aeolian sand within lacustrine sediment, reveals statistically significant spectral peaks that coincide with established lake level cycles in Lake Michigan and the Gleissberg sunspot cycle of minima. Longer cycles of ~ 800 and ~ 2200 years were also identified that correspond to solar cycles. Shorter cycles between 80 and 220 years suggest a link between coastal dune mobility, climate, and lake levels in the Lake Michigan basin. Radiocarbon-dated sedimentary contacts of lacustrine sediment overlying wetland sediment record the Nipissing transgression in the Lake Michigan basin. Lake level rise closely mimics the predicted uplift of the North Bay outlet, with lake level rise slowing when outflow was transferred to the Port Huron/Sarnia outlet. The Nipissing highstand was reached after 5000 cal (4.4 ka) BP.     

森林生态服务市场的开发

<正> 森林提供许多有价值的生态服务,诸如保护流域和生物多样性以及贮存碳素等,现已引起企业、政府乃至个人越来越多的关注,同时人们也意识到随着森林这些功能的退化甚至丧失所带来的危险和代价。这种退化既能引起洪水、山崩之类的局部灾难,也会导致全球气候变化之类的广泛影响。     

Influence of vegetation cover on sand transport by wind: field studies at Owens Lake,California

Field studies conducted at Owens Lake, California, provide direct measurements of sand flux on sand sheets with zero to 20 per cent cover of salt grass. Results from 12 different sand transport events show that aerodynamic roughness length and threshold wind shear velocity increase with vegetation cover as measured by vertically projected cover and roughness density (λ). This results in a negative exponential decrease in sediment flux with increasing vegetation cover such that sand transport is effectively eliminated when the vertically projected cover of salt grass is greater than 15 per cent. A general empirical model for the relation between sand flux and vegetation cover has been derived and can be used to predict the amount of vegetation required to stabilize sand dune areas. © 1998 John Wiley & Sons, Ltd.     

Soil water movement and nutrient cycling in semi-arid rangeland: vegetation change and system resilience

Recent decades have seen rapid intensification of cattle production in semi-arid savannah ecosystems, increasingly on formalized ranch blocks. As a result, vegetation community changes have occurred, notably bush encroachment (increased bush dominance) in intensively grazed areas. The exact causes of this vegetation change remain widely debated. Previous studies have suggested: (i) increased leaching of water and nutrients into the subsoil in intensively grazed areas provides deeper rooting bush species with a competitive advantage for soil water and nutrients, and (ii) nutrient leaching may be exacerbated by nutrient inputs from cattle dung and urine. Our research in the Eastern Kalahari showed that in infertile sandy soils both the magnitude of soil water and concentration of soil nutrients leached into the subsoil is largely unaffected by the ecological and biochemical effects of increased cattle use. We found that despite the high soil hydraulic conductivity ( &greaterno;12 cm h⁻¹), relatively high subsoil moisture contents and the restriction of water movement to matrix flow pathways prevent leaching losses beyond the rooting zone of savannah grass species. No significant differences in patterns of soil water redistribution were noted between bush dominant and grass dominant sites. We also found that the low nutrient status of Kalahari soils and leachate movement as matrix flow combine to allow nutrient adsorption on to soil particles. Nutrient adsorption ensures that nitrogen and phosphorus cycling remains topsoil dominated even following the removal of vegetation and direct nutrient inputs in cattle dung and urine. This conclusion refutes environmental change models that portray increases in the leaching of soil water and available nitrogen as a major factor causing bush encroachment. This provides a possible explanation for the now widely cited, but hitherto unexplained, resilience of dryland soils. We suggest that infertile sandy soils appear resilient to changes in soil water distribution and nutrient availability caused by increased cattle use. Hence, soil characteristics contribute to the resilience to permanent ecological change that is increasingly recognized as an attribute of semi-arid rangelands. © 1998 John Wiley & Sons, Ltd.     

Dynamic adaptive pathways in downscaled climate change scenarios

The parallel scenario process enables characterization of climate-related risks and response options to climate change under different socio-economic futures and development prospects. The process is based on representative concentration pathways, shared socio-economic pathways, and shared policy assumptions. Although this scenario architecture is a powerful tool for evaluating the intersection of climate and society at the regional and global level, more specific context is needed to explore and understand risks, drivers, and enablers of change at the national and local level. We discuss the need for a stronger recognition of such national-scale characteristics to make climate change scenarios more relevant at the national and local scale, and propose ways to enrich the scenario architecture with locally relevant details that enhance salience, legitimacy, and credibility for stakeholders. Dynamic adaptive pathways are introduced as useful tools to draw out which elements of a potentially infinite scenario space connect with decision-relevant aspects of particular climate-related and non-climate-related risks and response options. Reviewing adaptation pathways for New Zealand case studies, we demonstrate how this approach could bring the global-scale scenario architecture within reach of local-scale decision-making. Such a process would enhance the utility of scenarios for mapping climate-related risks and adaptation options at the local scale, involving appropriate stakeholder involvement.     

Spectrophotometric discrimination of river dissolved organic matter

There is a need to be able to differentiate the dissolved organic matter (DOM) fraction in river waters. Research in the 1970s and 1980s has attempted to utilize both absorbance and fluorescence to distinguish between DOM fractions in river waters, but both were limited by the available technology. Total organic carbon content has, therefore, been widely used as a standard method of measuring DOM concentration, although it has little power to differentiate DOM fractions. Recent advances in fluorescence spectrophotometry enable rapid and optically precise analysis of DOM. Here, we show how a combination of both fluorescence and absorbance can be used to discriminate statistically between spatial variations of DOM in tributaries in a small catchment of the Ouseburn, NE England. The results of the discriminant analysis suggest that about 70% of the samples can be correctly classified to its tributary. Discriminant function 1 explains 60·8% of the variance in the data and the fulvic‐like fluorescence intensity has the largest absolute correlation within this function; discriminant function 2 explains a further 21·5% of the variance and the fulvic‐like fluorescence emission wavelength has the largest absolute correlation within this function. The discriminant analysis does not correctly classify all tributaries every time, and successfully discriminates between the different tributaries 70% of the time. Occasions when the tributary waters are less well discriminated are due to either episodic pollution events (at two sites) or due to tributaries that have strong seasonal trends in spectrophotometric parameters, which allows the sites to be misclassified. Results suggest that spectrophotometric techniques have considerable potential in the discrimination of DOM in rivers. Copyright © 2002 John Wiley & Sons, Ltd.     

Detection of mRNA sequences homologous to the human glutathione peroxidase and rat cytochrome P-450IVA1 genes in Mytilus edulis

In this study we have used cloned gene probes for human glutathione peroxidase (GPX), rat cytochrome P-450IVA1 and rat cytochrome P-450IIE1 to detect homologous sequences in RNA from the hepato-pancreas of Mytilus edulis. The presence of sequences hybridising to the GPX and P-450IVA1 probes, but not to the P-450IIE1 probe, confirms the ancient origin of the former genes and indicates that conserved-sequence DNA probes from higher organisms can be used to examine the structure and function of genes of environmental interest in marine organisms.     

“Phasic” metropolitan settlers: a phase-based model for the distribution of households in US metropolitan regions

In this article, we develop a model for explaining spatial patterns in the distribution of households across metropolitan regions in the United States. First, we use housing consumption and residential mobility theories to construct a hypothetical probability distribution function for the consumption of housing services across three phases of household life span. We then hypothesize a second probability distribution function for the offering of housing services based on the distance from city center(s) at the metropolitan scale. Intersecting the two hypothetical probability functions, we develop a phase-based model for the distribution of households in US metropolitan regions. We argue that phase one households (young adults) are more likely to reside in central city locations, whereas phase two and three households are more likely to select suburban locations, due to their respective housing consumption behaviors. We provide empirical validation of our theoretical model with the data from the 2010 US Census for 35 large metropolitan regions.