|Abstracts on Global Climate Change|
Snow and glacier cover assessment in the high mountains of Sikkim Himalaya
HYDROLOGICAL PROCESSES 19:12 2375-2383
This study highlights the assessment of snow and glacier cover for possible inferences of global climate change impacts in high mountains like the Himalaya. The test catchment of the River Tista lies in the Sikkim state of the Indian Himalayan region, with steep mountains crossing nearly all ecozones, from subtropical to glacial. River flows are highly fluctuating, especially during the peak rainy season and snowmelt periods. Annual rainfall patterns are non-uniform and can cause large floods. Runoff and discharge downstream are highly dependent upon snow and glacier extent. The temporary storage of frozen water brings about a delay in seasonal runoff. Snow cover built up in the higher regions during the winter months melts in the spring-summer-autumn cycles and contributes to groundwater recharge. A spatial baseline inventory of snow cover/glacier, the permanent snowline and its short-term temporal changes in the remote high-mountain areas have been analysed using multidate Indian Remote Sensing Satellite data of 1992 to 1997. A geographic information system-based overlay has led to inferences on snow cover characteristics and the alignment, dimension, slope disposition, heights of the snout and associated features of each of the glaciers. Snow and glacier recession are to be monitored in future on a long-term basis to derive correlations with climate-change parameters. Copyright (c) 2005 John Wiley & Sons, Ltd.
The science, politics and economics of global climate change: Implications for the carbon sink projects
CURRENT SCIENCE 89:3 464-474
Drier summers cancel out the CO2 uptake enhancement induced by warmer springs
Angert, A Biraud, S Bonfils, C Henning, CC Buermann, W Pinzon, J Tucker, CJ Fung, I
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 102:31 10823-10827
An increase in photosynthetic activity of the northern hemisphere terrestrial vegetation, as derived from satellite observations, has been reported in previous studies. The amplitude of the seasonal cycle of the annually detrended atmospheric CO2 in the northern hemisphere (an indicator of biospheric activity) also increased during that period. We found, by analyzing the annually detrended CO2 record by season, that early summer (June) CO2 concentrations indeed decreased from 1985 to 1991, and they have continued to decrease from 1994 up to 2002. This decrease indicates accelerating springtime net CO2 uptake. However, the CO2 minimum concentration in late summer (an indicator of net growing-season uptake) showed no positive trend since 1994, indicating that lower net CO2 uptake during summer cancelled out the enhanced uptake during spring. Using a recent satellite normalized difference vegetation index data set and climate data, we show that this lower summer uptake is probably the result of hotter and drier summers in both mid and high latitudes, demonstrating that a warming climate does not necessarily lead to higher CO2 growing-season uptake, even in high-latitude ecosystems that are considered to be temperature limited.
Marmots on Great Basin mountaintops: Using genetics to test a biogeographic paradigm
Floyd, CH Van Vuren, DH May, B
ECOLOGY 86:8 2145-2153
Boreal mammals in the Great Basin have long been viewed as island-bound Pleistocene relicts because they occupy island-like patches of montane habitat separated by desert lowlands that presumably are impermeable to dispersal. Recent work, however, raised the possibility that dispersal among mountain ranges is an important process in the biogeography of boreal mammals in the Great Basin. We test this proposition using genetic variation in a representative species, the yellow-bellied marmot (Marinota flaviventris). A total of 332 marmots was sampled from 10 ranges and genotyped at six microsatellite loci. If the intervening desert lowlands are impermeable barriers to dispersal, then there should be no relationship between genetic distance and geographic distance among mountaintop populations, and genetic diversity should be diminished because gene flow would not be available to replace alleles lost over thousands of generations of isolation. Our results did not support these predictions. There was a strong correlation between genetic and geographic distance, demonstrating an isolation-by-distance pattern, and genetic diversity was high. Our results suggest that marmot populations in the Great Basin may be linked by dispersal, providing a mechanism to replenish genetic variation lost by drift. However, global climate change over the next several decades could make the desert lowlands more difficult to traverse, eventually transforming the boreal faunas of Great Basin mountaintops into the isolated relicts they were originally portrayed to be.
Are long-distance migrants constrained in their evolutionary response to environmental change? Causes of variation in the timing of autumn migration in a blackcap (S-atricapilla) and two garden warbler (Sylvia borin) populations
Pulido, F Widmer, M
BIRD HORMONES AND BIRD MIGRATIONS: ANALYZING HORMONES IN DROPPINGS AND EGG YOLKS AND ASSESSING ADAPTATIONS IN LONG-DISTANCE MIGRATION 1046: 228-241
Long-distance migratory birds often show little phenotypic variation in the timing of life-history events like breeding, molt, or migration. It has been hypothesized that this could result from low levels of heritable variation. If this were true, the adaptability of long-distance migratory birds would be limited, which would explain the vulnerability of this group of birds to environmental changes. The amount of phenotypic, environmental, and genetic variation in the onset of autumn migratory activity was assessed in two garden warbler (Sylvia borin) populations differing in breeding phenology and the length of the breeding season with the aim of investigating the effects of selection on the adaptability of long-distance migrants. High heritabilities and additive genetic variance components for the timing of autumn migration were found in both populations. Although genetic variation in the mountain population was lower than in the lowlands, this difference was not statistically significant. Moreover, no evidence was found for reduced levels of genetic variation in the garden warbler as compared to its sister species, the blackcap (S. atricapilla). Environmental variation, however, was markedly reduced in the garden warbler, suggesting that low levels of phenotypic variation typically found in long-distance migrants may be a consequence of environmental canalization of migratory traits. The buffering of environmental variation may be an adaptive response to strong stabilizing selection on the timing of migration. High environmental canalization of migration phenology in long-distance migrants could potentially explain low rates of immediate phenotypic change in response to environmental change.
Warming in Arctic intermediate and deep waters around Chukchi Plateau and its adjacent regions in 1999
Zhao, JP Gao, GP Jiao, YT
SCIENCE IN CHINA SERIES D-EARTH SCIENCES 48:8 1312-1320
Based on the data measured during Arctic scientific expedition of China in 1999, the characteristics of temperature and salinity distributions around the Chukchi Plateau and its adjacent regions have been studied. It was found that the intermediate water with temperature higher than 0.5 degrees C existed in all parts of a 640 km section with a maximum temperature of 0.85 degrees C indicating a strong signal of the warming in Arctic Intermediate Water in 1999. Two important phenomena are described in this paper. First, the temperature of warm water was horizontally nonuniform. In the area of Chukchi Plateau, the temperature was higher, the layer of warm water was thicker and the depth of the warm water core was shallower than those in the area of continental slope. The horizontal nonuniformity of the temperature distribution of warming water implies that the upward heat flux should also be nonuniform, thus exerting different effects on sea ice thickness, ice extent, and air-sea heat exchange. The mechanism to generate higher temperature in the plateau region was the bypassing of current around the plateau area caused by the special local topography, which restricted water exchange across the plateau and conserved heat in the water body. Second, the deep water down to 1400 m was also warming with a temperature increase of 0.2 degrees C. The warming in deep water reflects the occurrence of complicated heat redistribution processes in the intermediate water, which altered the thermal structure in the upper 1400 m. The warming data embody the obvious impact of global climate change on the Arctic Ocean and further studies are wanted.
Rates of erosion and topographic evolution of the Sierra Nevada, California, inferred from cosmogenic Al-26 and Be-10 concentrations
Stock, GM Anderson, RS Finkel, RC
EARTH SURFACE PROCESSES AND LANDFORMS 30:8 985-1006
Concentrations of cosmogenic Al-26 and Be-10 in cave sediments and bedrock surfaces, combined with studies of landscape morphology, elucidate the topographic history of the southern Sierra Nevada over the past 5 Ma. Caves dated by Al-26/Be-10 in buried sediments reveal that river incision rates were moderate to slow between c. 5 and 3 Ma (<= 0.07 mm a(-1)), accelerated between 3 and 1.5 Ma (c. 0.3 ram a(-1)), and then have subsequently become much slower (c. 0.02 mm a(-1)). Although the onset of accelerated incision coincides in time with both,postulated Pliocene tectonism and pronounced global climate change, we argue that it primarily represents the response to a discrete tectonic event between 3 and 5 Ma. Dated cave positions reveal that, prior to 3 Ma, river canyons displayed up to 1.6 km of local relief, suggesting that Pliocene rock uplift elevated pre-existing topography. Renewed incision beginning c. 3 Ma deepened canyons by up to 400 m, creating narrow inner gorges. Tributary streams exhibit strong convexities, indicating that the transient erosional response to Pliocene uplift has not yet propagated into upland surfaces. Concentrations of Al-26 and Be-10 in bare bedrock show that upland surfaces are eroding at slow rates of c. 0.01 mm a(-1). Over the past c. 3 Ma, upland surfaces eroded slowly while adjacent rivers incised rapidly, increasing local relief. Although relief production probably drove at least modest crestal uplift, considerable pre-Pliocene relief and low spatially averaged erosion rates suggest that climatically driven rock uplift is not sufficient to explain ail uplift implied by tilted markers at the western edge of the range. Despite the recent pulse of erosion, spatially averaged erosion rates are low, and have probably acted to preserve the broad topographic form of the Sierra Nevada throughout much of the late Cenozoic. Copyright (c) 2005 John Wiley & Sons, Ltd.
The case for carbon capture and storage
Stephens, JC Van der Zwaan, B
ISSUES IN SCIENCE AND TECHNOLOGY 22:1 68-76
Human activity releases approximately 25 billion tons of carbon dioxide into the atmosphere every year, building up the levels of greenhouse gases that are responsible for global climate change. The world’s forests store about 2 or 3 billion tons of that output annually, and the ocean absorbs 7 billion tons. Itis estimated that another 5 to 10 billion tons, as much as 40% of man-made carbon dioxide, could be removed from the atmosphere and safely stored away. Methods of storage are being researched, for example underground geological storage. Issues of safety and cost and feasibility need to be addressed before the government can push for carbon capture and storage.
Early tectonic uplift of the northern Tibetan Plateau
Dai, SA Fang, XM Song, CH Gao, JP Gao, DL Li, JJ
CHINESE SCIENCE BULLETIN 50:15 1642-1652
The Hexi Corridor is the northmost foreland basin of the Tibetan Plateau and its formation is controlled by the northern marginal fault of Tibet, Altyn Tagh Fault (ATF)-North Qilian Shan marginal Fault (NQF), and the southern Kuantan Shan-Longshou Shan Fault (KLF). So its study is important to understanding the mechanism of Tibet formation and its influence on global climate change. The oldest Cenozoic sediments in the Corridor is the Huoshaogou Formation which consists of terrigenous fine conglomerate, sandstone, sandy mudstone and mudstone, depositing in alluvial to lacustrine and fan delta sedimentary environments. Detailed paleomagnetic measurements of this sequence at Yumen clearly reveal eleven pairs of normal and reversed polarities. Fossil mammals found around the section support that most of the observed polarities can be well correlated with chrons between 13n and 18r of the standard geomagnetic polarity time scale, yielding ages of 40.2-33.35 Ma. The mean declinations of this sequence and its immediately above stratigraphy indicate an 18.3 degrees rapid clockwise rotation of the Hexi Corridor. Since this sequence has been strongly folded and is capped by an angular unconformity, we think that the presence of the thick alluvial fan conglomeration at the bottom of the foreland basin may indicate the initial deformation and uplift of the northern Qilian Shan. This process could occur at latest at 40.2 Ma, driven by the faults NQF and KLF that thrust onto the Hexi corridor respectively from its southern and northern margins. These faults are in an early response to the collision of India with Asia, while the unconformable termination and rotation of the Huoshaogou Formation at similar to 33.35 Ma indicate other early episode of rapid tectonic deformation and uplift of the northern Tibet.
Drought, tree rings, and reservoir design
JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION 41:4 949-958
Droughts constitute one of the most important factors affecting the design and operation of water resources infrastructure. Hydrologists ascertain their duration, severity, and pattern of recurrence from instrumental records of precipitation or streamflow. Under suitable conditions, and with proper analysis, tree rings obtained from long living, climate sensitive species of trees can extend instrumental records of streamflow and precipitation over periods spanning several centuries. Those tree-ring “reconstructions” provide a valuable insight about climate variability and drought occurrence in the Holocene, and yield long term hydrological data useful in the design of water infrastructure. This work presents a derivation of drought risk based on a renewal model of drought recurrence, a brief review of the basic theory of tree-ring reconstructions, and a stochastic model for optimizing the design of water supply reservoirs. Examples illustrate the methodology developed in this work and the supporting role that tree-ring reconstructed streamflow can play in characterizing hydrologic variability.