Climate and environmental evolution scenarios for the Meuse/Haute-Marne région, France

This document assesses the climate and environmental evolution of the Meuse/Haute-Marne (M/HM) site and of neighbouring regions from the end of the Saalian glaciation (ca. 150,000 years Before Present (B.P.), OIS 6) to 1 million years After Present (A.P.). It relies not only on the multidisciplinary study of a number of climatic and palaeoenvironmental archives, but also on various numerical climate simulations. The biological, sedimentological and geochemical indicators used showed that, during the last 150,000 years, significant climatic and environmental variations have occurred over pluri- to infra-millennial timescales. The mean annual temperature of the M/HM region (currently 10°C) has varied from interglacial maxima in the order of 12°C to glacial minima ranging from -6°C to -12°C. The vegetation has oscillated between stages of forest cover during interglacial periods to stages of herb cover with scarce trees (tundra to bush tundra) that were adapted to the cold and dryness of glacial maxima. The soil and the subsoil, ice-free during interglacial periods, were subject to deep multi-year freezing as soon as average annual temperatures fell below 0°C for several months. During the last glacial maximum, some 18,000 years B.P., the permafrost may have reached a depth of 120 m in the M/HM region [Van Vliet Lanoe, 2004]. With regard to the future climate evolution of the region, several scenarios are possible. If the disturbance caused to the climate system by the combustion of fossil fuels is not taken into account, it is likely that the current interglacial period will continue for several thousands or even tens of thousands of years. Nevertheless, the initiation of our current climate cooling, between 5,000 and 2,000 years B.P., as recorded by the dynamics of the vegetation, shows that we are moving toward the end of an interglacial period. Numerical simulations carried out under the EC BIOCLIM Project [Texier et at., 2003; Texier et al., 2007] have indicated that our interglacial period will last for another 50,000 years A.P., whereas chronological models bring that figure down to 3,000-20,000 years A.P. However, the prospects change if the impact of anthropic disturbances on the climate, which are thought to have become significant since the beginning of the 20 th century, are taken into account and if those disturbances are extrapolated to the future. According to the BIOCLIM simulations, which represent the impact of a substantial injection of carbon dioxide into the atmosphere as a result of fossil fuel consumption, the end of our interglacial period may be delayed by 100,000 or even 180,000 years. Other contributions, e.g. methane and sulphate aerosols, are likely to modify this conclusion to only a limited degree. During the next few centuries ahead, the climate of the M/HM region would therefore move towards warmer temperatures than the current temperate ones. The consequence of that climate-warming process would be felt over several hundreds of thousands of years. In particular, it would take at least 600,000 years, if not 850,000 years for the regional climate to undergo a cooling sufficient to induce a glaciation similar in magnitude to those peak glacial episodes that have occurred over the last 850,000 years.