Abstracts on Global Climate Change

Feb 2007

Global cooling forced increase in marine strontium isotopic ratios: Importance of mica weathering and a kinetic approach

Li, GJ Chen, J Ji, JF Liu, LW Yang, JD Sheng, XF


The knowledge of how and why marine Sr-87/Sr-86 ratios changed helps understand the impacts of many processes on the global biogeochemical cycle in the geological past. Here we examine the possible influence of global cooling on the evolution of marine Sr-87/Sr-86 curve by a kinetic approach. The importance of mica weathering is emphasized due to its high content of radiogenic strontium and low activation energy in weathering reaction. Since the activation energy determines the sensitivity of weathering rate in response to temperature changes, global cooling will increase the Sr-87/Sr-86 ratio of continental flux by relatively preferential weathering of mica. Based on the average strontium contents and Sr-87/Sr-86 ratios of the mica minerals in the exposed upper continental crust, a kinetic model is established to survey the response of riverine Sr-87/Sr-86 to the changes of global temperatures. The model result indicates that the increase of riverine Sr-87/Sr-86 caused by global cooling can solely account for most of the increase in seawater Sr-87/Sr-86 since 3.4 Myr B.P. This finding emphasizes that the weathering kinetics is an important mechanism relating the global climate change to marine Sr-87/Sr-86 curve; and the marine Sr-87/Sr-86 curve should be used with great care in the climate-weathering-tectonic connections. (c) 2006 Elsevier B.V All rights reserved.

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Inverse flood risk modelling under changing climatic conditions

Cunderlik, JM Simonovic, SP


One of the most significant anticipated consequences of global climate change is the increased frequency of hydrologic extremes. Predictions of climate change impacts on the regime of hydrologic extremes have traditionally been conducted using a top-down approach. The top-down approach involves a high degree of uncertainty associated with global circulation model (GCM) outputs and the choice of downscaling technique. This study attempts to explore an inverse approach to the modelling of hydrologic risk and vulnerability to changing climatic conditions. With a focus targeted at end-users, the proposed approach first identifies critical hydrologic exposures that may lead to local failures of existing water resources systems. A hydrologic model is used to transform inversely the main hydrologic exposures, such as floods and droughts, into corresponding meteorological conditions. The frequency of critical meteorological situations is investigated under present and future climatic scenarios by means of a generic weather generator. The weather generator, linked with GCMs at the last step of the proposed methodology, allows the creation of an ensemble of different scenarios, as well as an easy updating, when new and improved GCM outputs become available. The technique has been applied in Ontario, Canada. The results show significant changes in the frequency of hydro-climatic extremes under future climate scenarios in the study area. Copyright (c) 2007 John Wiley & Sons, Ltd.

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Changes in biotic interactions and climate determine recruitment of Jeffrey pine along an elevation gradient

Gworek, JR Wall, SBV Brussard, PF


The mechanisms by which climate affects recruitment and loss of plants and the interactions between those plants and other organisms (e.g., pathogens, granivores, seed dispersers) have seldom been studied in the context of plant response to climate change. We examined how climate influences Jeffrey pine (Pines jeffreyi) recruitment, mortality, and species interactions at three elevation zones (low, mid, high) across its elevation range (1550-2470 m) in the semi-arid Carson Range of western Nevada. Local climate was correlated with several aspects of stand structure, including smaller trees, slower growth rates, greater predation by seed insects, and higher tree mortality at low elevation. Cone crop was not affected by elevation, but there were more mature trees and more filled seeds per cone at mid- and high elevations. Populations of seed-caching rodents were largest at mid-elevation, but sufficient rodents were present at all elevations to cause rapid removal and dispersal of pine seeds. Seedling emergence from rodent caches was greatest at low and middle elevation, but seedling survival was best at middle and high elevations. The number of saplings was greatest at mid-elevation sites. These results suggest a retracting population at low elevation (high adult tree mortality and low recruitment), a rapidly expanding population at mid-elevation (low adult tree mortality and high recruitment), and a slowly expanding population at high elevation (low adult tree mortality and low recruitment). These demographic patterns foreshadow a shift in distribution upslope over future decades, driven by changes in climate and facilitated by biotic interactions. (c) 2006 Elsevier B.V. All rights reserved.

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On the sensitivity of radiative forcing from biomass burning aerosols and ozone to emission location

Naik, V Mauzerall, DL Horowitz, LW Schwarzkopf, MD Ramaswamy, V Oppenheimer, M


Biomass burning is a major source of air pollutants, some of which are also climate forcing agents. We investigate the sensitivity of direct radiative forcing due to tropospheric ozone and aerosols (carbonaceous and sulfate) to a marginal reduction in their ( or their precursor) emissions from major biomass burning regions. We find that the largest negative global forcing is for 10% emission reductions in tropical regions, including Africa (- 4.1 mWm(-2) from gas and - 4.1 mWm(-2) from aerosols), and South America (- 3.0 mWm(-2) from gas and - 2.8 mWm(-2) from aerosols). We estimate that a unit reduction in the amount of biomass burned in India produces the largest negative ozone and aerosol forcing. Our analysis indicates that reducing biomass burning emissions causes negative global radiative forcing due to ozone and aerosols; however, regional differences need to be considered when evaluating controls on biomass burning to mitigate global climate change.

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Effects of climate change on water resources in Tarim River Basin, Northwest China

Chen, YN Li, WH Xu, CC Hao, XM


Based on hydrology, temperature, and precipitation data from the past 50 years, the effects of climate change on water resources in Tarim River Basin in Northwest China were investigated. The long-term trends of the hydrological time series were detected using both parametric and nonparametric techniques. The results showed that the increasing tendency of the temperature has a 5% level of significance, and the temperature increased by nearly VC over the past 50 years. The precipitation showed a significant increase in the 1980s and 1990s, and the average annual precipitation exhibited an increasing trend with a magnitude of 6.8 mm per decade. A step change occurred in both the temperature and precipitation time series around 1986. The streamflow from the headwater of the Tarim River exhibited a significant increase during the last 20 years. The increase in temperature, precipitation, and streamflow may be attributed to global climate change.

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Exploring linkages between abiotic oceanographic processes and a top-trophic predator in an Antarctic ecosystem

Proffitt, KM Garrott, RA Rotella, JJ Siniff, DB Testa, JW

ECOSYSTEMS 10:1 119-126

Climatic variation affects the physical and biological components of ecosystems, and global-climate models predict enhanced sensitivity in polar regions, raising concern for Antarctic animal populations that may show direct responses to changes in sea-ice distribution and extent, or indirect responses to changes in prey distribution and abundance. Here, we show that over a 30-year period in the Ross Sea, average weaning masses of Weddell seals, Leptonychotes weddellii, varied strongly among years and were correlated to large-scale climatic and oceanographic variations. Foraging success of pregnant seals (reflected by weaning mass the following pupping season) increased during summers characterized by reduced sea-ice cover and positive phases of the southern oscillation. These results demonstrate a correlation between environmental variation and an important life history characteristic (weaning mass) of an Antarctic marine mammal. Understanding the mechanisms that link climatic variation and animal life history characteristics will contribute to understanding both population dynamics and global climatic processes. For the world’s most southerly distributed mammal species, the projected trend of increasing global climate change raises concern because increasing sea-ice trends in the Ross Sea sector of Antarctica will likely reduce populations due to reduced access to prey as expressed through declines in body condition and reproductive performance.

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Consistency of interdecadal variation in the summer monsoon over eastern China and heterogeneity in springtime surface air temperatures

Xu, XD Shi, XH Xie, L Wang, YF


This study investigates the consistency of interdecadal variations in the East Asian summer monsoon (EASM) and changes in the heterogeneous structure of sea/land springtime surface air temperature (SAT) over eastern China and the adjacent ocean (including the South China Sea and part of the Western Pacific Ocean). A profile of the summer mean meridional wind over eastern China for the past 40 years shows a coherent interdecadal weakening trend for the EASM. The decadal-scale (11-year running mean) summertime (June-August) wind and springtime (March-May) SAT fields are decomposed using the empirical orthogonal function (EOF) method. The results indicate that both the leading eigenvector of the decadal-scale meridional wind and that for the SAT over East Asia account for more than 70% of the total variance. Their time coefficients show a similar trend, with the transition from negative to positive values occurring around 1978; i.e., the EASM turned from a stronger phase to a weaker phase around 1978. The springtime sea/land SAT distribution before and after 1978 also showed a shift in interdecadal trends. Therefore, the south-low/north-high nature of the principal component of springtime SAT over eastern China is closely related to the progressive weakening of the EASM. Our results suggest that within the context of the regional impact of global climate change, heterogeneous changes in the regional springtime sea/land SAT in eastern Asia might in part have led to a weakening of the effect of sea/land thermal driving on the EASM.

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Soil carbon and nitrogen stores and storage potential as affected by land-use in an agro-pastoral ecotone of northern China

Zhou, ZY Sun, OJ Huang, JH Li, LH Liu, P Han, XG


Equilibrium carbon stock is the result of a balance between inputs and outflows to the pool. Changes in land-use are likely to alter such balance, resulting in different carbon stores under different land-use types in addition to the impacts of global climate change. In an agro-pastoral ecotone of Inner Mongolia, northern China, we investigated productivity and belowground carbon and nitrogen stores under six different types of land-uses, namely free grazing (FG), grazing exclusion (GE), mowing (MW), corn plantation (CP), fallow (FL), and alfalfa pasture (AP), and their impacts on litter and fine roots in semiarid grassland ecosystems. We found that there were great variations in aboveground net primary production (ANPP) across the six land-use types, with CP having markedly high ANPP; the FG had significantly reduced soil organic carbon (SOC) and nitrogen stores (SON) to 100 cm depth compared with all other types of land uses, while very little litter accumulation was found on sites of the FG and CP. The top 20 cm of soils accounted for about 80% of the root carbon and nitrogen, with very little roots being found below 50 cm. About 60% of SOC and SON were stored in the top 30 cm layer. Land-use change altered the inputs of organic matters, thus affecting SOC and SON stores accordingly; the MW and GE sites had 59 and 56% more SOC and 61% more SON than the FG. Our estimation suggested that restoring severely degraded and overgrazed grasslands could potentially increase SOC and SON stores by more than 55%; conversion from the native grasses to alfalfa could potentially double the aboveground biomass production, and further increase SOC and SON stores by more than 20%. Our study demonstrated significant carbon and nitrogen storage potential of the agro-pastoral ecotone of northern China through land-use changes and improved management in the context of mitigating global climate change.

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The potential bioavailability of organic C, N, and P through enzyme hydrolysis in soils of the Mojave Desert

Nadeau, JA Qualls, RG Nowak, RS Blank, RR


Increases in the growth rate of plants and microbes in the Mojave Desert in response to predicted increases in precipitation and CO2 due to global climate change may induce nutrient limitations. This study was designed to measure the pool of potentially bioavailable nutrients in soils of the Mojave Desert. Soils were collected from shrub and interspace microsites and then subjected to amendment with buffered solutions of an excess of various enzymes. The products of each enzyme reaction were then measured and the maximum quantity of hydrolyzable substrates was calculated. In interspace and shrub microsite soils, respectively, 14.5 and 9.7% of the organic C in the form cellulose, 60.0-97.8% and 61.2-100.0% of the organic N in the form protein, and 44.0 and 57.5% of the organic P was hydrolyzable. There were significant differences between microsites for hydrolyzable substrate using all enzyme amendments, except protease. We propose that accumulations of hydrolyzable organic C, N, and P in the Mojave Desert could be a result of the persistently dry soil conditions often found in desert ecosystems and the immobilization of enzymes, which may result in low diffusivity of soil substrates and enzymes and, accordingly, little degradation of organic C, N, and P. Alternatively, rapid nutrient cycling and immobilization by soil microorganisms could account for accumulations of organic C, N, and P. Further refinement of the methods used in this study could lead to a valuable tool for the assessment of potential bioavailability of nutrients in a variety of soils.

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The cost of postponing biodiversity conservation in Mexico

Fuller, T Sanchez-Cordero, V Illoldi-Rangel, P Linaje, M Sarkar, S


Though Neotropical countries are the most species rich in the world, their biodiversity is threatened by the loss of native vegetation. Land conversion in Mexico during the last 30 years has been extensive and is representative of that of other developing countries. However, the effects of land use change on the required size and configuration of an adequate biological conservation area network are largely unknown. It is shown here that endemic mammals in Mexico could have been protected considerably more economically if a conservation plan had been implemented in 1970 than is possible today due to extensive conversion of primary habitats. Analysis of the distributions of 86 endemic mammal species in 1970, 1976, 1993, and 2000 indicates that the distributions of 90% of the species shrank during this 30-year period. At each time step, optimal conservation area networks were selected to represent all species. 90% more land must be protected after 2000 to protect adequate mammal habitat than would have been required in 1970. In addition, under a realistic conservation budget, 79% fewer species can be represented adequately in a conservation area network after 2000 compared to 1970. This provides an incentive for rapid conservation action in Mexico and other biodiversity hotspots with comparable deforestation rates, including Burma, Ecuador, Indonesia, the Philippines, and Sri Lanka. Due to ongoing habitat degradation, the efficiency of a conservation plan decreases with delays in its implementation. (c) 2006 Elsevier Ltd. All rights reserved.

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The Arctic as a trigger for glacial terminations

Martinson, DG Pitman, WC

CLIMATIC CHANGE 80:3-4 253-263

We propose a hypothesis to explain the very abrupt terminations that end most of the glacial episodes. During the last glaciation, the buildup and southerly expansion of large continental ice-sheets in the Northern Hemisphere and extensive cover of sea ice in the N. Pacific and the N. Atlantic imposed a much more zonal climatic circulation system than exists today. We hypothesize that this, in combination with the frigid (dry) polar air led to a significant decrease in freshwater runoff into the Arctic Ocean. In addition the freshwater contribution of the fresher Pacific water was completely eliminated by the emergence of the Bering Strait (sill depth 50 m). As the Arctic freshwater input was depleted, regions of the Arctic Ocean lost surface stability and eventually overturned, bringing warmer deep water to the surface where it melted the overlying sea ice. This upwelled water was quickly cooled and sank as newly formed deep water. For sustained overturn events, such as might have occurred during the peak of very large glacial periods (i.e. the last glacial maximum), the voluminous deep water formed would eventually overflow into the Nordic Seas and North Atlantic necessitating an equally voluminous rate of return flow of warmer surface waters from the North Atlantic thus breaking down the Arctic’s zonal isolation, melting the expansive NA sea ice cover and initiating oceanic heating of the atmosphere over the ice-sheets bordering the NA. We suggest that the combined effect of these overturn-induced events in concert with a Milankovitch warming cycle, was sufficient to drive the system to a termination. We elaborate on this proposed sequence of events, using the model for the formation of the Weddell Sea polynya as proposed by Martinson et al. (1981) and various, albeit sparse, data sets from the circum-Arctic region to apply and evaluate this hypothesis to the problem of glacial terminations.

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The California current system during the last 136,000 years: response of the North Pacific High to precessional forcing

Yamamato, M Yamamuro, M Tanaka, Y


Alkenone sea surface temperature (SST) records were generated from the Ocean Drilling Program’s (ODP) Sites 1014 and 1016 to examine the response of the California Current System to global climate change during the last 136ka. The temperature differences between these sites (Delta SSTNEP = SSTODP10144-SSTODP1016) reflected the intensity of the California Current and varied between 0.4 and 6.1 degrees C. A high ASSTNEP (weaker California Current) was found for late marine isotope stage (MIS) 2 and early MIS 5e, while a low ASSTNEP (stronger California Current) was detected for mid-MIS 5e and MIS 1. Spectral analysis indicated that this variation pattern dominated 23- (precession) and 30-ka periods. Comparison of the Delta SSTNEP and SST based on data from core MD01-2421 at the Japan margin revealed anti-phase variation; the high ASSTNEP (weakening of the California Current) corresponded to the low SST at the Japan margin (the southward displacement of the NW Pacific subarctic boundary), and vice versa. This variation was synchronous with a model prediction of the tropical El Nino-Southern Oscillation behavior. These findings suggest that the intensity of the North Pacific High varied in response to precessional forcing, and also that the response has been linked with the changes of tropical ocean-atmosphere interactions. (c) 2007 Elsevier Ltd. All rights reserved.

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Relative importance of estuarine flatfish nurseries along the Portuguese coast

Cabral, HN Vasconcelos, R Vinagre, C Franca, S Fonseca, V Maia, A Reis-Santos, P Lopes, M Ruano, M Campos, J Freitas, V Santos, PT Costa, MJ


The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but their occurrence differed among the estuaries, R flesus only occurred in estuaries north of the Tejo estuary (39 degrees N), S. solea was quite rare along the southern Portuguese coast (south of 37 degrees 30’N), S. senegalensis occurred in estuaries throughout the coast, but its abundance varied considerably, and the occurrence of M. hispidus was limited to the Sado estuary and Ria Formosa. A Correspondence Analysis was performed to evaluate the relationships between flatfish species abundance and geomorphologic and hydrologic characteristics of estuaries (latitude, freshwater flow, estuarine area, intertidal area, mean depth and residence time). Abiotic characteristics (depth, temperature, salinity, sediment type) of nursery grounds of each flatfish species were also evaluated. Results showed that some estuaries along the Portuguese coast have nursery grounds used by several flatfish species (e.g. Ria de Aveiro, Sado, estuary), while in other systems a segregation was noticed, with juveniles of different species occurring in distinct estuarine areas (e.g. Minho and Mondego estuaries). This emphasizes the relevance of niche overlap, but the potential for competition may be considerably minimized by differences in resource use patterns and by an extremely high abundance of resources. Peak densities of flatfishes recorded in nurseries areas along the Portuguese coast were within the range of values reported for other geographical areas. Inter-annual abundance variability of all the species in the Tejo and Sado estuaries was extremely high, with a drastic decrease in P flesus in the Tejo estuary, probably related to higher water temperature in recent years due to global climate change. (c) 2006 Elsevier B.V. All rights reserved.

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Climatological aspects of convective parameters from the NCAR/NCEP reanalysis

Brooks, HE Anderson, AR Riemann, K Ebbers, I Flachs, H


Annual cycles of convectively important atmospheric parameters have been computed for a variety of from the National Center for Atmospheric Research (NCAR)/National Centers for Environmental Prediction (NCEP) global reanalysis, using 7 years of reanalysis data. Regions in the central United States show stronger seasonality in combinations of thermodynamic parameters than found elsewhere in North America or Europe. As a result, there is a period of time in spring and early summer when climatological mean conditions are supportive of severe thunderstorms. The annual cycles help in understanding the large-scale processes that lead to the combination of atmospheric ingredients necessary for strong convection. This, in turn, lays groundwork for possible changes in distribution of the environments associated with possible global climate change. (c) 2006 Elsevier B.V. All rights reserved.

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Do elevated temperature and CO2 generally have counteracting effects on phenolic phytochemistry of boreal trees?

Veteli, TO Mattson, WJ Niemela, P Julkunen-Tiitto, R Kellomaki, S Kuokkanen, K Lavola, A


Global climate change includes concomitant changes in many components of the abiotic flux necessary for plant life. In this paper, we investigate the combined effects of elevated CO2 (720 ppm) and temperature (+2 K) on the phytochemistry of three deciduous tree species. The analysis revealed that elevated CO2 generally stimulated increased carbon partitioning to various classes of phenolic compounds, whereas an increase in temperature had the opposite effect. The combined effects of both elevated CO2 and temperature were additive, i.e., canceling one another’s individual effects. Obviously, the effects of global climate change on leaf chemistry must simultaneously consider both temperature and CO2. If these results are generally applicable, then the counteracting effect of the temperature is likely to play a major role in alpine, boreal, and arctic zones in determining the balance between populations of plants and herbivores.

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