991 resultados para Climatic change
Resumo:
The impact of future climate change on the glaciers in the Karakoram and Himalaya (KH) is investigated using CMIP5 multi-model temperature and precipitation projections, and a relationship between glacial accumulation-area ratio and mass balance developed for the region based on the last 30 to 40 years of observational data. We estimate that the current glacial mass balance (year 2000) for the entire KH region is -6.6 +/- 1 Gta(-1), which decreases about sixfold to -35 +/- 2 Gta(-1) by the 2080s under the high emission scenario of RCP8.5. However, under the low emission scenario of RCP2.6 the glacial mass loss only doubles to -12 +/- 2 Gta(-1) by the 2080s. We also find that 10.6 and 27 % of the glaciers could face `eventual disappearance' by the end of the century under RCP2.6 and RCP8.5 respectively, underscoring the threat to water resources under high emission scenarios.
Resumo:
The end of the Palaeozoic is marked by two mass-extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative C-13 anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high-resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn-extinction and post-extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal-beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.
Resumo:
Due to the greenhouse effect,a long term warming of the atmosphere is expected. For most people the last relative mild winters and the previous two hot summers are clear signals for such a climatic change. Changes in species compositions and the sudden arrival of southern species in the North Sea are explained as consequences of the greenhouse effect. Comparing the situation in the last decades an attempt is made in this article to show the natural variability in the occurrence and to give an answer to the above question.
Resumo:
1. 192016;2823;2825;3834;1110 90.5-96%53.1-81.7%61.7%53.8%50-53.6% 2. 2, 5000 1 2, 5381 B.P1, 9335 B.P.3620m 2 1, 9335 B.P.1, 2426 B.P.;3080m 3 1, 2426 B.P.;3277m;;2440m 8000 B.P.;; 6000 B.P.; 1,18059990 B.P.8000B.P.
Resumo:
General Circulation Models (GCMs) may be useful in estimating the ecological impacts of global climatic change. We analyzed seasonal weather patterns over the conterminous United States and determined that regional patterns of rainfall seasonality appear to control the distributions of the Nation's major biomes. These regional patterns were compared to the output from three GCMs for validation. The models appear to simulate the appropriate seasonal climates in the northern tier of states. However, the spatial extent of these regions is distorted. None of the models accurately portrayed rainfall seasonalities in the southern tier of states, where biomes are primarily influenced by the Bermuda High.
Resumo:
DSDP Site 480 in the Gulf of California represents a paleoclimatic record of great potential significance. Much of the 152-meter section is varved, which means that proxy records of climatic change can be analyzed with unusual precision on a variety of time scales. In this paper we present pollen and dinoflagellate evidence that suggests that the base of the section is much older than was previously thought. We propose a basal date of between 300,000 and 350,000 YBP.
Resumo:
EXTRACT (SEE PDF FOR FULL ABSTRACT): Current projections of the response of the biosphere to global climatic change indicate as much as 50 to 90% spatial displacement of extratropical biomes. The mechanism of spatial shift could be dominated either by competitive displacement of northern biomes by southern biomes or by drought-induced dieback of areas susceptible to change. The current suite of global biosphere models cannot distinguish between these two processes, hence the need for a mechanistically based biome model. The first steps have been taken toward development of a rule-based, mechanistic model of regional biomes at a continental scale. ... The model is in an early stage of development and will require several enhancements, including: explicit simulation of potential evapotranspiration, extension to boreal and tropical biomes, a shift from steady-state to transient dynamics, and validation on other continents.
Resumo:
C02N2O ; (IGBP)415IG8P(NECTNortheast China Transect)IGBP 2001;C02; (1).22.34.93 gkg-18.91.20 gkg-13.520.881 g.kg-113.10.78%;1.140.250g.kg-l10.90.79%(r=0.993P<0.001) (2).(126131)61.913.84 gkg-110. 882.236g. kg-111912610.51.97 gkg-l1. 350.327 gkg-111311914.61.65 gkg-12.070.342g.kg-11111137.991.51 gkg-10.510.216 gkg-1 (3).PHr=0.677P<0.001r=0.712P<0.001 (4).r=0.454P=0.026; r=0.473P=0.020 (5).CO21.28%;29.67%CO2 (6).r=0.695 (P<0.001)0.636(P<0.001) (7). (8).0.682(P<0.001)0.688(P<0.001)r=0.241P=0.256; r=0.366P=0.079r=0.390p=0.044 (9).CO25.55%3.84% (10);;NO3--N 4.75.6% (ll)10CO2CO2
