查看更多>>摘要：The Earth behaves as a highly coupled, interdependent system of components and processes - all of which operate on a multitude of time and spatial scales. Humans - rather than simply affecting or being affected by the natural environment - are a central component in the Earth system. Within the Earth system, there are feedbacks and teleconnections that operate on a planetary scale, and in which humans are directly involved. This article presents examples of such feedback systems and of human interactions in the Earth system, and describes some of the research infrastructure necessary to pursue Earth System Science.
查看更多>>摘要：Although Venus is often referred to as the most Earth-like of the terrestrial planets, its runaway greenhouse has resulted in a dry, hot, uninhabitable surface. Its surface geology is complex, with volcanoes ranging from < 5 to > 500km across, lava flows fields > 800km across, mountain belts, rift zones, and terrains unique to Venus such as tesserae and coronae. It surface has an average crater retention age similar to Earth's continents, but the random nature of the impact crater population renders it useless in providing time constraints for the geologic history of Venus. At some point in the past, Venus lost an ocean's worth of water. If this water persisted on the surface for long periods of time in Venus's early history, life may have evolved. Untangling the complex history of Venus, and what it reveals for the evolution of habitable planets, will require future missions to the surface.
查看更多>>摘要：The last ten years have been characterized by a renewed worldwide effort of exploration of the Solar System, which has produced spectacular new data and concluded the "discovery" phase. The next decades will focus on refinement of knowledge and will tackle specific problems such as the boundary conditions for the onset and maintenance of life on planetary bodies. Final understanding of the formation and evolution of planetary systems is expected, also based on the observation of extra solar systems and possible detection of "habitable" extra solar planets.
查看更多>>摘要：Water is the key to our existence on this planet and it is involved in nearly all biological, geological, and chemical processes. Life on Earth depends very much on the remarkable properties of water. The availability of freshwater is for many regions one of the key concerns in connection with global climate change. The atmosphere contains only about 0.001% of the water available on our planet. Despite this small amount its horizontal and vertical distribution plays a key role in the global water cycle and the Earth's climate. The atmosphere has direct connections to most of the other reservoirs and steers the redistribution of water between them with an average turnover time of about 10 days. Evaporation over the oceans exceeds precipitation and over land evapotranspiration amounts only to 2/3 of the precipitation reaching the ground. Consequently, there is a net flux of water from the oceans towards the continents, of course via the atmosphere, which has the largest overall volume of fluxes. Water is present in the atmosphere as solid, liquid, or gas. Water vapour is the most important greenhouse gas in the atmosphere and, in addition, changes of water phase and cloud-radiation interaction contribute strongly to the global energy cycle. Water is also a physically and chemically integral part of other biogeochemical cycles. Although there have been large efforts and improvements in recent years, uncertainties in quantifying the components of the atmospheric water cycle still exist. Observational capabilities on the global scale are not satisfactory at present, but the advent of new satellites devoted to the global observation of precipitation and cloud systems along with dedicated modelling projects certainly will improve the situation. Progress is urgently needed to adequately contribute to the answer of one of the central questions in the context of global warming: Is the hydrological cycle accelerating?.
查看更多>>摘要：This is the text of a lesson explaining the concepts of kinetic gas theory, diffusion theory and thermodynamics used in describing the formation and growth of aerosol and cloud droplets in the atmosphere. The classical Koehler theory and its extensions are derived in a step-wise approach, starting from clean laboratory systems and ending with the polluted atmosphere. The meaning of the Koehler theory is analysed. Some comments follow regarding the central role the theory still plays in atmospheric research today; it indeed forms a formal framework to link air pollution and climate change.
查看更多>>摘要：A review is given of the dynamical mechanisms responsible for the monsoon circulation over West Africa. Features of the circulation are first described, including the seasonal displacement of the rain bands, the structure of the heat low over the Sahara, the meridional circulation to the south and the associated zonal jets. Simple theories for the zonal-mean meridional circulation are then presented, using the principles of angular momentum conservation, thermal wind balance and moist convective equilibrium. The application of these theories to the West African monsoon reveals a sensitivity to the low-level meridional gradient of equivalent potential temperature, which helps explain observed variability in the monsoon onset. Processes leading to east-west asymmetries in the circulation are also described, and mechanisms linking West African rainfall anomalies with remote events in the tropics are discussed. These dynamical considerations are then placed in the broader context of the ongoing AMMA research program.
查看更多>>摘要：This paper is presents a concise review of regional climate modeling, from its ensuing stages in the late 1980s to the most recent developments. A tremendous progress has been achieved in improving the performance of regional climate models, which are currently used by a growing research community for a wide range of applications, from process studies to paleoclimate and future climate simulations. Basic concepts underlying the nested modeling technique, along with the current debate on outstanding issues in regional climate modeling, are discussed. Finally, perspectives of future developments in this rapidly evolving research area are briefly outlined. An extensive, reference list is provided to support the discussion.
查看更多>>摘要：Vegetation change is involved in climate change through both forcing and feedback processes. Emissions of CO, from past net deforestation are estimated to have contributed approximately 0.22-0.51 Wm(-2) to the overall 1.46 Wm(-2) radiative forcing by anthropogenic increases in CO2 up to the year 2000. Deforestation-induced increases in global mean surface albedo are estimated to exert a radiative forcing of 0 to -0.2 Wm(-2), and dust emissions from land use may exert a radiative forcing of between approximately +0.1 and -0.2 Wm(-2). Changes in the fluxes of latent and sensible. heat due to tropical deforestation are simulated to have exerted other local warming effects which cannot be quantified in terms of a Wm(-2) radiative forcing, with the potential for remote effects through changes in atmospheric circulation. With tropical deforestation continuing rapidly, radiative forcing by surface albedo change may become less useful as a measure of the forcing of climate change by changes in the physical properties of the land surface. Although net global deforestation is continuing, future scenarios used for climate change prediction suggest that fossil fuel emissions of CO, may continue to increase at a greater rate than land use emissions and therefore continue to increase in dominance as the main radiative forcing. The CO2 rise may be accelerated by up to 66% by feedbacks arising from global soil carbon loss and forest dieback in Amazonia as a consequence of climate change, and Amazon forest dieback may also exert feedbacks through changes in the local water cycle and increases in dust emissions.
查看更多>>摘要：The global biosphere has begun to change fundamentally as a consequence of human actions. This change can be understood as a consequence of a major transition in the evolution of life on Earth, the emergence of human language, which opened up new pathways of biological information transmission. The challenge facing the humans species now is to not just suffer the consequences of this change, but to develop a science of Earth system analysis that will allow the collective, globally networked reflective capacity of humans to chart paths into the future that are sustainable. Global observation and computer modelling are important elements of this process. Such models for the biosphere predict large-scale reorganisation of the functional composition of the terrestrial biosphere under strong anthropogenic climate change. Considering the advent of humans and of global change on the background of the past evolution of life on Earth, it is obvious that the co-evolution between geosphere and biosphere that has characterised Earth history in the past has expanded to include the anthroposphere as a third interacting element.
查看更多>>摘要：Clouds are the largest uncertainty in future projections of climate. This critically important uncertainty is addressed by studying the role of atmospheric electromagnetics in cloud initiation. Cloud droplets are produced by cloud condensation nuclei. However, the formation of cloud condensation nuclei ultimately relies on physical mechanisms on the atomic and molecular scale which influence the meta-stable phase transition between condensation and evaporation. At these small spatial scales, electrical forces are important. A small yet non-zero influence of electric fields and energetic charged particles on the formation of cloud condensation nuclei would have important consequences for climate change, as small changes in cloud initiation can lead to large changes in global temperature. The current knowledge on the role of atmospheric electromagnetics and energetic charged particles in cloud initiation and climate change is summarised and recommendations for future work are proposed.
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