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Kaplan J.O.,Ecole Polytechnique Federale de Lausanne | Krumhardt K.M.,Ecole Polytechnique Federale de Lausanne | Ellis E.C.,University of Maryland Baltimore County | Ruddiman W.F.,University of Virginia | Lemmen C.,Institute For Kustenforschung
Holocene | Year: 2011

Humans have altered the Earth's land surface since the Paleolithic mainly by clearing woody vegetation first to improve hunting and gathering opportunities, and later to provide agricultural cropland. In the Holocene, agriculture was established on nearly all continents and led to widespread modification of terrestrial ecosystems. To quantify the role that humans played in the global carbon cycle over the Holocene, we developed a new, annually resolved inventory of anthropogenic land cover change from 8000 years ago to the beginning of large-scale industrialization (ad 1850). This inventory is based on a simple relationship between population and land use observed in several European countries over preindustrial time. Using this data set, and an alternative scenario based on the HYDE 3.1 land use data base, we forced the LPJ dynamic global vegetation model in a series of continuous simulations to evaluate the impacts of humans on terrestrial carbon storage during the preindustrial Holocene. Our model setup allowed us to quantify the importance of land degradation caused by repeated episodes of land use followed by abandonment. By 3 ka BP, cumulative carbon emissions caused by anthropogenic land cover change in our new scenario ranged between 84 and 102 Pg, translating to c. 7 ppm of atmospheric CO2. By ad 1850, emissions were 325-357 Pg in the new scenario, in contrast to 137-189 Pg when driven by HYDE. Regional events that resulted in local emissions or uptake of carbon were often balanced by contrasting patterns in other parts of the world. While we cannot close the carbon budget in the current study, simulated cumulative anthropogenic emissions over the preindustrial Holocene are consistent with the ice core record of atmospheric δ 13CO 2 and support the hypothesis that anthropogenic activities led to the stabilization of atmospheric CO 2 concentrations at a level that made the world substantially warmer than it otherwise would be.© The Author(s) 2010. Source


Ocana V.,Massachusetts Institute of Technology | Zorita E.,Institute For Kustenforschung | Heimbach P.,The Texas Institute
Journal of Geophysical Research: Oceans | Year: 2016

Global mean sea level (GMSL) has been rising since (at least) the nineteenth century and the rate of rise may be increasing. Several studies that attempt to explain the long-term trend of GMSL during the instrumental record share the common assumption that this trend is deterministic in nature and different from natural variations. Here we show that the trend can alternatively be explained, at least in part, as being caused by random variations within the coupled ocean-atmosphere-cryosphere system, and hence not having a deterministic origin. These random trends, which add to externally forced changes (e.g., through anthropogenic climate change), are a consequence of the integrated character of GMSL, which is the cumulative addition of temporal contributions that exhibit random character, and whose integration results in GMSL variations with persistence on decadal-centennial time scales. The generation of trends by integration of random stationary noise (i.e., even in a constant climate) is a robust and fundamental feature of stochastically forced systems with memory. The integrated character of GMSL results in an intrinsic difficulty in distinguishing internal from externally forced trends. © 2016. American Geophysical Union. All Rights Reserved. Source


Berg G.M.,Stanford University | Mills M.M.,Stanford University | Long M.C.,Stanford University | Bellerby R.,University of Bergen | And 8 more authors.
Global Biogeochemical Cycles | Year: 2011

Surface δ 15N PON increased 3.92 ± 0.48‰ over the course of 20 days following additions of iron (Fe) to an eddy in close proximity to the Antarctic Polar Front in the Atlantic sector of the Southern Ocean. The change in δ 15N PON was associated with an increase in the >20 μm size fraction, leading to a maximal difference of 6.23‰ between the >20 m and <20 m size fractions. Surface δ 13C POC increased 1.18 ± 0.31‰ over the same period. After a decrease in particulate organic matter in the surface layer, a second phytoplankton community developed that accumulated less biomass, had a slower growth rate and was characterized by an offset of 1.56‰ in δ 13C POC relative to the first community. During growth of the second community, surface δ 13C POC further increased 0.83 ± 0.13‰. Here we speculate on ways that carboxylation, nitrogen assimilation, substrate pool enrichment and community composition may have contributed to the gradual increase in δ 13C POC associated with phytoplankton biomass accumulation, as well as the systematic offset in δ 13C POC between the two phytoplankton communities. Copyright 2011 by the American Geophysical Union. Source


Stott P.A.,UK Met Office | Christidis N.,UK Met Office | Otto F.E.L.,University of Oxford | Sun Y.,National Climate Center | And 7 more authors.
Wiley Interdisciplinary Reviews: Climate Change | Year: 2016

Extreme weather and climate-related events occur in a particular place, by definition, infrequently. It is therefore challenging to detect systematic changes in their occurrence given the relative shortness of observational records. However, there is a clear interest from outside the climate science community in the extent to which recent damaging extreme events can be linked to human-induced climate change or natural climate variability. Event attribution studies seek to determine to what extent anthropogenic climate change has altered the probability or magnitude of particular events. They have shown clear evidence for human influence having increased the probability of many extremely warm seasonal temperatures and reduced the probability of extremely cold seasonal temperatures in many parts of the world. The evidence for human influence on the probability of extreme precipitation events, droughts, and storms is more mixed. Although the science of event attribution has developed rapidly in recent years, geographical coverage of events remains patchy and based on the interests and capabilities of individual research groups. The development of operational event attribution would allow a more timely and methodical production of attribution assessments than currently obtained on an ad hoc basis. For event attribution assessments to be most useful, remaining scientific uncertainties need to be robustly assessed and the results clearly communicated. This requires the continuing development of methodologies to assess the reliability of event attribution results and further work to understand the potential utility of event attribution for stakeholder groups and decision makers. © 2016 Wiley Periodicals, Inc. Source


Newton A.,Institute of Air Research | Newton A.,University of Algarve | Icely J.,University of Algarve | Cristina S.,University of Algarve | And 26 more authors.
Estuarine, Coastal and Shelf Science | Year: 2014

The paper gives an overview of some of the large, shallow, semi-enclosed coastal systems (SECS) in Europe, These SECS are important both from the ecological and the economic perspective (socio-ecological systems) and provide many valuable ecosystem goods and services.Although some of the systems are transitional waters under the Water Framework Directive, this is not the case for all of the systems. The paper adopts a Driver-Pressure-State-Impact-Response approach to analyse the ecological status, vulnerability and future perspectives of these systems in the context of global change. © 2013. Source

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