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31.
Pavel E. Tarasov Rachid Cheddadi Joel Guiot Sytze Bottema Odile Peyron Jordina Belmonte Vittoria Ruiz-Sanchez Fatima Saadi Simon Brewer 《第四纪科学杂志》1998,13(4):335-344
An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm and cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span. © 1998 John Wiley & Sons, Ltd. 相似文献
32.
We propose an analytic model that allows rapid computation of the secondary ion production due to electron impact from the primary photo-production in the ionosphere of Titan. The model parameters are given for each of the 5 major ion productions (N+2, CH+4, N+, CH+3, N++2) as well as for the electron production. 相似文献
33.
Michel Magny Jacques‐Louis de Beaulieu Ruth Drescher‐Schneider Boris Vannire Anne‐Vronique Walter‐Simonnet Laurent Millet Gilles Bossuet Odile Peyron 《第四纪科学杂志》2006,21(4):311-320
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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35.
A. Jost D. Lunt M. Kageyama A. Abe-Ouchi O. Peyron P. J. Valdes G. Ramstein 《Climate Dynamics》2005,24(6):577-590
The analyses of low-resolution models simulations of the last glacial maximum (LGM, 21 kyr BP) climate have revealed a large
discrepancy between all the models and pollen-based palaeoclimatic reconstructions. In general, the models are too warm relative
to the observations, especially in winter, where the difference is of the order of 10°C over western Europe. One of the causes
of this discrepancy may be related to the low spatial resolution of these models. To assess the impact of using high-resolution
models on simulated climate sensitivity, we use three approaches to obtain high-resolution climate simulations over Europe:
first an atmospheric general circulation model (AGCM) with a stretched grid over Europe, second a homogeneous T106 AGCM (high
resolution everywhere on the globe) and last a limited area model (LAM) nested in a low-resolution AGCM. With all three methods,
we have performed simulations of the European climate for present and LGM conditions, according to the experimental design
recommended by the Palaeoclimate Modeling Intercomparison Project (PMIP). Model results have been compared with updated pollen-based
palaeoclimatic indicators for temperature and precipitation that were initially developed in PMIP. For each model, a low-resolution
global run was also performed. As expected, the low-resolution simulations underestimate the large cooling indicated by pollen
data, especially in winter, despite revised slightly warmer reconstructions of the temperatures of the coldest month, and
show results in the range of those obtained in PMIP with similar models. The two high-resolution AGCMs do not improve the
temperature field and cannot account for the discrepancy between model results and data, especially in winter. However, they
are able to reproduce trends in precipitation more closely than their low-resolution counterparts do, but the simulated climates
are still not as arid as depicted by the data. Conversely, the LAM temperature results compare well with climate reconstructions
in winter but the simulated hydrological cycle is not consistent with the data. Finally, these results are discussed in regard
of other possible causes for discrepancies between models and palaeoclimatic reconstructions for the LGM European climate. 相似文献
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The stakes for alleviating poverty and avoiding unbridled climate change are inextricably linked. Climate change impacts will slow down and may even reverse trends in poverty reduction. The pathways consistent with global warming of no more than 2?°C require strategies for poverty alleviation to make allowance for the constraint of low-carbon development. Existing climate funds have failed to target poverty alleviation as a high-priority strategy for adaptation or as a component of low-carbon development. This article proposes a funding window as part of the Green Climate Fund in order to foster synergies targeting greater satisfaction of basic needs, while making allowance for adaptation and mitigation. This financial mechanism is based on indicators of the satisfaction of basic needs and could respond to the claims of the developing countries, which see alleviating poverty as the first priority in climate negotiations. It defines a country continuum, given that there are poor people everywhere; all developing countries are therefore eligible with a mechanism of this sort.Policy relevanceThe Intergovernmental Panel on Climate Change (IPCC) calls for substantial emissions reductions and adaptation strategies over the next decades to reduce the high risks of severe impacts of climate change over the 21st century. Industrialized countries and developing countries alike recognize the need to mitigate climate change and to adapt to it. But they face many challenges that lead to an ‘emissions gap’ between an emissions level consistent with the 2?°C increase limit and the voluntary pledges that they have made thus far in the climate negotiations (United Nations Environment Programme. (2014). The Emissions Gap Report 2014. A UNEP synthesis report). In this arena, many developing countries underline that their first domestic priority is the satisfaction of basic needs. In the run-up to the next climate negotiations at the 21st Conference of the Parties (COP 21) in Paris, the proposed poverty-adaptation-mitigation funding window could contribute to alleviate the conflict between development and climate goals in developing countries. In this sense, it could spur developing countries to integrate more ambitious emissions limitations pledges into their Intended Nationally Determined Contributions. This could in turn entice industrialized countries to act similarly. In the end, it could pave the way to an ambitious climate agreement in Paris at COP 21. 相似文献
38.
The modern analogue technique (MAT) was applied to six pollen sequences from the Belledonne Massif (northwestern French Alps) to estimate the effect of altitude and local parameters on pollen‐based climate reconstruction during the Lateglacial and the early Holocene. The six sites (Le Vivier (345 m a.s.l.), Les Etelles (700 m a.s.l.), La Coche (980 m a.s.l.), Montendry (1330 m a.s.l.), Le Grand Leyat (1660 m a.s.l.), La Gouille (1800 m a.s.l.)) are located in different vegetation belts (mixed deciduous woods, conifer woods, alpine pastures with maple). The main vegetation changes in the past are recorded at each site. The evolution of four climate parameters (coldest month temperature, warmest month temperature, mean annual temperature, annual precipitation) was quantitatively inferred from pollen data using MAT. The curves obtained were compared to the Les Etelles site, which was the least affected by non‐local pollen transport. The results show consistent trends for the climate parameters reconstructed at the different sites. However, the reconstruction does not indicate a decrease in temperature values related to the increasing elevation. Difficulties in reconstructing the altitudinal variations of climate parameters from pollen data during the periods studied are discussed and perspectives for improvement are considered. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
39.
The application of computer technology has permitted more and more problems of dynamical astronomy to be solved more easily, quickly, and accurately. In this area, numerical integration is often very efficient, and sometimes essential. There is often, however, a temptation to choose numerical integration simply because it is the easiest way to attack the problem. Sometimes this works to the detriment of a satisfactory understanding of the physics of the problem under study. It is particularly the case for the free, or Eulerian, oscillations. The forces that create such a motion are not of gravitational origin and are not even conservative. The theory can only specify the frequencies of oscillation, not their amplitudes nor phases. The case is complicated when the free oscillations interact with gravitationally-forced oscillations, a situation that is almost inevitable, since nothing is isolated in the Universe. The first author has particularly studied this problem in the case of the rotation of the Moon, and published the first credible determinations of the lunar free libration. In this kind of problem, the observations have to be used and care must to be taken to create no spurious free librations in the results by using numerical integrations to describe the other related motions. A differential correction of the starting conditions to fit the observations does not necessarily give any valid information on the real free oscillation contained in the data. An analytical model is necessary, if the goal of the research is to understand the origins and characteristics of an Eulerian oscillation in such a system. 相似文献
40.
Odile Calame 《Earth, Moon, and Planets》1976,15(3-4):343-352
Among the lunar laser range measurements obtained during the past six years at McDonald Observatory, those available cover the period August 1969-November 1974, being 1377 normal observations made on the three Apollo reflectors and that of Lunokhod II. The fit of these data led to a rms residual of 55 cm. In this study, a large number of parameters have been resolved, including the geocentric coordinates of the telescope, the selenocentric coordinates of each of the reflectors, as well as orbital elements of the Moon. In addition, the interest has been directed more specially towards the study of the rotational motion of the Moon and particularly the problem of its free librations. The performed resolutions give the evidence of the three modes of free oscillations. The determined amplitudes arise to 1.7 in longitude and 0.5 and 8.7 in latitude, with the respective periods of 2.9 years, 27.3 days and 75 years. In connection with these parameters, the fittings determined also the most of part of elements of lunar gravitational field: the moment of inertia parameters and, and a number of the third degree harmonics. These new results should now permit a research on the implications of these oscillations effects, concerning the impact history of the Moon and the properties of its internal structure. On the basis of the amplitudes determined here, one can already estimate an order of the magnitude for theQ dissipation coefficient comparable with that determined from seismic studies of the Moon. 相似文献