156 research outputs found
Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)
This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and
Technology (CICYT), the
Spanish National Parks agency, the European Commission, the
Spanish Ministry of Science, and the European
Social Fund
Revealing the last 13,500 years of environmental history from the multiproxy record of a mountain lake (Lago Enol, northern Iberian Peninsula)
This is the author's accepted manuscript. The final publication is available at Springer via http://dx.doi.org/10.1007/s10933-009-9387-7.We present the Holocene sequence from Lago Enol (43°16′N, 4°59′W, 1,070 m a.s.l.), Cantabrian Mountains, northern Spain. A multiproxy analysis provided comprehensive information about regional humidity and temperature changes. The analysis included sedimentological descriptions, physical properties, organic carbon and carbonate content, mineralogy and geochemical composition together with biological proxies including diatom and ostracod assemblages. A detailed pollen study enabled reconstruction of variations in vegetation cover, which were interpreted in the context of climate changes and human impact. Four distinct stages were recognized for the last 13,500 years: (1) a cold and dry episode that includes the Younger Dryas event (13,500–11,600 cal. year BP); (2) a humid and warmer period characterizing the onset of the Holocene (11,600–8,700 cal. year BP); (3) a tendency toward a drier climate during the middle Holocene (8,700–4,650 cal. year BP); and (4) a return to humid conditions following landscape modification by human activity (pastoral activities, deforestation) in the late Holocene (4,650–2,200 cal. year BP). Superimposed on relatively stable landscape conditions (e.g. maintenance of well established forests), the typical environmental variability of the southern European region is observed at this site.The Spanish Inter-Ministry Commission of Science and
Technology (CICYT), the
Spanish National Parks agency, the European Commission, the
Spanish Ministry of Science, and the European
Social Fund
Emergent risks in the Mt. Everest region in the time of anthropogenic climate change
In April and May 2019, as a part of the National Geographic and Roxel
Perpetual Planet Everest Expedition, the most interdisciplinary scientific ever
was launched. This research identified changing dynamics, including emergent
risks resulting from natural and anthropogenic change to the natural system. We
have identified compounded risks to ecosystem and human health, geologic
hazards, and changing climate conditions that impact the local community,
climbers, and trekkeers in the future. This review brings together perspectives
from across the biological, geological, and health sciences to better
understand emergent risks on Mt. Everest and in the Khumbu region.
Understanding and mitigating these risks is critical for the ~10,000 people
living in the Khumbu region, as well as the thousands of visiting trekkers and
the hundreds of climbers who attempt to summit each year.Comment: 21 pages, 2 figure
Asian dust-storm activity dominated by Chinese dynasty changes since 2000 BP
The Asian monsoon (AM) played an important role in the dynastic history of China, yet it remains unknown whether AM-mediated shifts in Chinese societies affect earth surface processes to the point of exceeding natural variability. Here, we present a dust storm intensity record dating back to the first unified dynasty of China (the Qin Dynasty, 221–207 B.C.E.). Marked increases in dust storm activity coincided with unified dynasties with large populations during strong AM periods. By contrast, reduced dust storm activity corresponded to decreased population sizes and periods of civil unrest, which was co-eval with a weakened AM. The strengthened AM may have facilitated the development of Chinese civilizations, destabilizing the topsoil and thereby increasing the dust storm frequency. Beginning at least 2000 years ago, human activities might have started to overtake natural climatic variability as the dominant controls of dust storm activity in eastern China
An Overview of Physical Risks in the Mt. Everest Region
In April and May 2019, as part of National Geographic and Rolex's Perpetual Planet Everest
Expedition, an interdisciplinary scientific effort conducted a suite of research on the mountain
and recognized many changing dynamics, including emergent risks resulting from natural and
anthropogenic changes to the biological system. In this paper, the diverse research teams
highlight risks to ecosystem and human health, geologic hazards, and changing climbing
conditions that may affect the local community, climbers, and trekkers in the future. This Primer
brings together perspectives from across the atmospheric, biological, geological, and health
sciences to better understand emergent risks on Mt. Everest and in the Khumbu region.
Understanding these risks is critical for the ~10,000 people living in the Khumbu region, the
thousands of visiting trekkers, and the hundreds of climbers who attempt to summit each year
Millennial changes in North American wildfire and soil activity over the last glacial cycle
Climate changes in the North Atlantic region during the last glacial cycle were dominated by the slow waxing and waning of the North American ice sheet as well as by intermittent Dansgaard-‐Oeschger (DO) events. However prior to the last deglaciation, little is known about the response of North American vegetation to such rapid climate changes and especially about the response of biomass burning, an important factor for regional changes in radiative forcing. Here we use continuous, high-‐resolution ammonium (NH4+) records derived from the NGRIP and GRIP ice cores to document both North American NH4+ background emissions from soils and wildfire frequency over the last 110,000 yr. Soil emissions increased on orbital timescales with warmer climate, related to the northward expansion of vegetation due to reduced ice-‐covered areas. During Marine Isotope Stage (MIS) 3 DO warm events, a higher fire recurrence rate is recorded, while NH4+ soil emissions rose only slowly during longer interstadial warm periods, in line with slow ice sheet shrinkage and delayed ecosystem changes. Our results indicate that sudden warming events had little impact on NH4+ soil emissions and NH4+ aerosol transport to Greenland during the glacial but triggered a significant increase in the frequency of fire occurrence.This paper has greatly benefitted from the Sir Nicholas Shackleton fellowship, Clare Hall, University of Cambridge, U.K., awarded to HF in 2014. The Division for Climate and Environmental Physics, Physics Institute, University of Bern acknowledges the long-‐term financial support of ice core research by the Swiss National Science Foundation (SNSF) and the Oeschger Centre for Climate Change Research. EW is supported by a Royal Society professorship. NGRIP is directed and organized by the Department of Geophysics at the Niels Bohr Institute for Astronomy, Physics and Geophysics, University of Copenhagen. It is supported by funding agencies in Denmark (SNF), Belgium (FNRS-‐CFB), France (IPEV and INSU/CNRS), Germany (AWI), Iceland (RannIs), Japan (MEXT), Sweden (SPRS), Switzerland (SNSF) and the USA (NSF, Office of Polar Programs).This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/ngeo249
Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic
The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch (~11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity (~3.5 °C and ~1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes, although the inflow can compensate on decadal timescales by becoming more saline. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change
Paleoclimate Implications for Human-Made Climate Change
Paleoclimate data help us assess climate sensitivity and potential human-made
climate effects. We conclude that Earth in the warmest interglacial periods of
the past million years was less than 1{\deg}C warmer than in the Holocene.
Polar warmth in these interglacials and in the Pliocene does not imply that a
substantial cushion remains between today's climate and dangerous warming, but
rather that Earth is poised to experience strong amplifying polar feedbacks in
response to moderate global warming. Thus goals to limit human-made warming to
2{\deg}C are not sufficient - they are prescriptions for disaster. Ice sheet
disintegration is nonlinear, spurred by amplifying feedbacks. We suggest that
ice sheet mass loss, if warming continues unabated, will be characterized
better by a doubling time for mass loss rate than by a linear trend. Satellite
gravity data, though too brief to be conclusive, are consistent with a doubling
time of 10 years or less, implying the possibility of multi-meter sea level
rise this century. Observed accelerating ice sheet mass loss supports our
conclusion that Earth's temperature now exceeds the mean Holocene value. Rapid
reduction of fossil fuel emissions is required for humanity to succeed in
preserving a planet resembling the one on which civilization developed.Comment: 32 pages, 9 figures; final version accepted for publication in
"Climate Change at the Eve of the Second Decade of the Century: Inferences
from Paleoclimate and Regional Aspects: Proceedings of Milutin Milankovitch
130th Anniversary Symposium" (eds. Berger, Mesinger and Sijaci
Nothing Lasts Forever: Environmental Discourses on the Collapse of Past Societies
The study of the collapse of past societies raises many questions for the theory and practice of archaeology. Interest in collapse extends as well into the natural sciences and environmental and sustainability policy. Despite a range of approaches to collapse, the predominant paradigm is environmental collapse, which I argue obscures recognition of the dynamic role of social processes that lie at the heart of human communities. These environmental discourses, together with confusion over terminology and the concepts of collapse, have created widespread aporia about collapse and resulted in the creation of mixed messages about complex historical and social processes
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