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w 22 | Focus cnrs I international magazine q Since 1850, weather stations, supplemented in the last 30 years by satellite observations, have been gathering increasingly precise data on the climate. Yet the lack of older historical records makes it difficult to understand the complexity of our planet’s climate mechanism. “Fortunately, there exist several natural archives that bear the trace of past climates—called climate proxies,” says Valérie Masson-Delmotte, a paleoclimatologist at the LSCE.1 “These include coral for example, but also sediments, icecaps, glaciers, stalagmites, soils, seashells, and trees, which hold key data on the conditions that prevailed when they formed.” As part of the EPICA program,2 ice core samples extracted from a depth of up to 3270 meters near the South Pole have yielded information on the Antarctic climate and atmospheric composition as far back as 800,000 years ago. This data has shed light on the history of the past eight terrestrial climate cycles, which alternate between cold (glacial) and warm (interglacial) periods, depending on the parameters of the Earth’s orbit. “In order to interpret this information,” specifies Masson-Delmotte, “we must understand as accurately as possible how climate signals are recorded in the biological, chemical, and physical parameters of different environments. To do so, we rely on in-situ observations like those carried out by my colleague Dominique Genty in the caves of southwestern France to elucidate the processes that link the surface climate, water infiltration, calcite formation, and the composition of stalagmites.” Analyses are performed using increasingly 03 04 Ice core samples from the Antarctic are used to reconstruct the past composition of the Earth’s atmosphere. 05 Cross-section of a stalagmite from Villars Cave in southwestern France, showing evidence of climatic variations between 82,000 and 30,000 years ago. sophisticated methods that can be applied to ever smaller samples. “These natural archives must then be dated, a delicate task, in order to combine the various climatic records obtained for a given period.” It is then important to cross- reference this data with information collected using models that simulate both past and future climate change. “This can be important to evaluate climate sensitivity, for example, which is the change in surface temperature induced by a disruption of the Earth’s energy balance,” explains Masson-Delmotte. Not surprisingly, past climatic variations are also of interest to historians—the last glacial period marked the beginning of the colonization of many new territories by our distant ancestors. 01. L aboratoire des sciences du climat et de l’environnement (CNRS / CEA / UVSQ). 02. European Project for Ice Coring in Antarctica. contact information: Valérie Masson-Delmotte > valerie.masson@lsce.ipsl.fr 03 04 05 © L. AUGUSTIN/CNRS Phototh èque © D. Genty © p. carsten /getty The Hidden Face of Climate Research To study the climate, researchers use a combination of satellite measurements, sample analyses, observations in the field, and digital simulations. Deep into   into the past   past


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