[en] Climate sciences have become extraordinary instruments for the media and the politicians. The climate debates regularly put forward the question of our knowledge: what do we know exactly, what can we assert, and of what are we doubtful? A subsidiary question would be: are scientists telling us the truth? For the scientific community, there is no doubt that human activities are modifying the Earth's atmosphere composition and that the surface temperature of the Earth has globally warmed up since the beginning of the 20. century. We live on a planet with a finite dimension: fossil resources are not forever and wastes are accumulating. Is the greenhouse effect already changing climate? Is it the only factor which will control the climate evolution? What would be the natural rhythm of climate? Are scientists capable to unravel the wheels of the climate machine? What is the situation of the climate change under way with respect to the turbulences of the past? What is an acceptable climate change? This book gives a clear answer to each of these questions as far as the answer is known. (J.S.)

[en] We describe briefly here the main mechanisms and time scales involved in natural and anthropogenic climate variability, based on quantitative paleo-climatic reconstructions from natural archives and climate model simulations: the large glacial-interglacial cycles of the last million years (the Quaternary), lasting typically a hundred thousand years, triggered by changes in the solar radiation received by the Earth due to its position around the Sun; the century-long climatic changes occurring during last glacial period and triggered by recurrent iceberg discharges of the large northern hemisphere ice caps, massive freshwater flux to the north Atlantic, and changes in the ocean heat transport. We show the strong coupling between past climatic changes and global biogeochemical cycles, namely here atmospheric greenhouse gases. We also discuss the decadal climatic fluctuations during the last thousand years, showing an unprecedented warming attributed to the anthropogenic greenhouse gas emissions. We show the range of atmospheric greenhouse concentrations forecasted for the end of the 21. century and the climate model predictions for global temperature changes during the 21. century. We also discuss the possible climatic changes at longer time scales involving the possibility of north Atlantic heat transport collapse (possibility of abrupt climate change), and the duration of the current interglacial period. (author)

[en] This chapter assesses palaeoclimatic data and knowledge of how the climate system changes over interannual to millennial time scales, and how well these variations can be simulated with climate models. Additional palaeoclimatic perspectives are included in other chapters. Palaeoclimate science has made significant advances since the 1970s, when a primary focus was on the origin of the ice ages, the possibility of an imminent future ice age, and the first explorations of the so-called Little Ice Age and Medieval Warm Period. Even in the first IPCC assessment, many climatic variations prior to the instrumental record were not that well known or understood. Fifteen years later, understanding is much improved, more quantitative and better integrated with respect to observations and modelling. After a brief overview of palaeoclimatic methods, including their strengths and weaknesses, this chapter examines the palaeoclimatic record in chronological order, from oldest to youngest. This approach was selected because the climate system varies and changes over all time scales, and it is instructive to understand the contributions that lower-frequency patterns of climate change might make in influencing higher-frequency patterns of variability and change. In addition, an examination of how the climate system has responded to large changes in climate forcing in the past is useful in assessing how the same climate system might respond to the large anticipated forcing changes in the future. Cutting across this chronologically based presentation are assessments of climate forcing and response, and of the ability of state-of-the-art climate models to simulate the responses. Perspectives from palaeoclimatic observations, theory and modelling are integrated wherever possible to reduce uncertainty in the assessment. Several sections also assess the latest developments in the rapidly advancing area of abrupt climate change, that is, forced or unforced climatic change that involves crossing a threshold to a new climate regime (e.g., new mean state or character of variability), often where the transition time to the new regime is short relative to the duration of the regime

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[en] Atmospheric methane is an important greenhouse gas and a sensitive indicator of climate change and millennial-scale temperature variability. Its concentrations over the past 650,000 years have varied between ∼ 350 and ∼ 800 parts per 10⁹ by volume (p.p.b.v.) during glacial and interglacial periods, respectively. In comparison, present-day methane levels of ∼ 1,770 p.p.b.v. have been reported. Insights into the external forcing factors and internal feedbacks controlling atmospheric methane are essential for predicting the methane budget in a warmer world. Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is ∼ 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by ∼100,000 yr glacial - interglacial cycles up to ∼400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles. We suggest that changes in the strength of tropical methane sources and sinks (wetlands, atmospheric oxidation), possibly influenced by changes in monsoon systems and the position of the intertropical convergence zone, controlled the atmospheric methane budget, with an additional source input during major terminations as the retreat of the northern ice sheet allowed higher methane emissions from extending peri-glacial wetlands. Millennial-scale changes in methane levels identified in our record as being associated with Antarctic isotope maxima events are indicative of ubiquitous millennial-scale temperature variability during the past eight glacial cycles. (authors)

[en] The objective of this collective book is to provide the public with elements of information showing that there is an actual risk that climate-related risk severely affects mankind during the next decades. A first part proposes a summary of the most recent works which place the problematic of climate change within its scientific context at different time and space scales. The second part describes the nature and properties of various greenhouse gases. The third part addresses the future evolution of some regional climates which are relevant for impact studies (possible evolutions during this century and beyond, associated uncertainties). The fourth part proposes a rather detailed presentation of possible consequences of local climate changes. The authors assess possible ecological consequences, analyse human and social risks and measures which could make these climate changes more bearable. The fifth part identifies actions to be performed to reduce carbon dioxide emissions in the atmosphere, and the possibility to correct modifications we have imposed to the planet climate. The last part analyses the evolution of world awareness of the climate issue

[en] The first volume of this collective publication gathers contributions on techniques used to reconstruct past climates. The chapters address the climate system operation and history (evolution, mechanisms, the atmosphere, oceans, ground and marine biosphere, cryo-sphere, lithosphere), propose an introduction to geochronology, present and discuss various dating methods (carbon 14, K-Ar and Ar-Ar methods, dating of corals and other geological samples based the disequilibrium between uranium and thorium isotopes, use of magnetic stratigraphy, dendro-chronology, dating of ice archives), discuss how to reconstruct atmosphere physics and circulation, address the use and properties of different interfaces (air-ice with polar ices, air-plants with pollen, air-soil with loessic sequences as markers of atmospheric circulation or reconstruction of paleo-climates with speleothems, air-lake, plant-atmosphere, air-plant, air-water, air-ice in tropical glaciers), and discuss the use of paleo-oceanography data. The second volume gathers contributions in which the authors present the most recent approaches used to reconstruct the operation of the climate system in the past by using present observations and models. The chapters address the biochemistry of the climate system during the last million of years, the relationship between cryo-sphere and sea level, the climate at the scale of geological times, modelling approaches in paleoclimatology, the Precambrian climate, the Phanerozoic climates, the relationship between climate and astronomic cycles, the description and mechanisms of quick climate variability, the Holocene and the anthropogenic perturbation, and the evolution from past climates to future climates

[en] The European Nuclear Young Generation Forum (ENYGF) is the event organised every 2 years within the European Nuclear Society - Young Generation Network (ENS-YGN) for European young professionals and students. It consists in 3 days of conferences (plenary sessions, workshops, panel sessions, technical and poster session), 1 day of technical tours and 1 day of cultural visits. ENYGF 2015 is dedicated to the dual aspect of the relationship between nuclear power and environment: the impact of nuclear activities on the environment and the contribution of nuclear energy to fight climate change. A great deal of this document is composed of the slides of the presentations