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The Last Glacial Maximum
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We used 5704 14C, 10Be, and 3
He ages that span the interval from 10,000 to 50,000 years ago
(10 to 50 ka) to constrain the timing of the Last Glacial Maximum (LGM) in terms of global
ice-sheet and mountain-glacier extent. Growth of the ice sheets to their maximum positions
occurred between 33.0 and 26.5 ka in response to climate forcing from decreases in northern
summer insolation, tropical Pacific sea surface temperatures, and atmospheric CO2. Nearly all
ice sheets were at their LGM positions from 26.5 ka to 19 to 20 ka, corresponding to minima in
these forcings. The onset of Northern Hemisphere deglaciation 19 to 20 ka was induced by an
increase in northern summer insolation, providing the source for an abrupt rise in sea level. The
onset of deglaciation of the West Antarctic Ice Sheet occurred between 14 and 15 ka, consistent
with evidence that this was the primary source for an abrupt rise in sea level ~14.5 ka.
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The late Precambrian greening of the Earth
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Many aspects of the carbon cycle can be assessed from temporal changes in the 13C/12C ratio of oceanic bicarbonate. 13C/12C can temporarily rise when large amounts of 13C-depleted photosyn- thetic organic matter are buried at enhanced rates1, and can decrease if phytomass is rapidly oxidized2 or if low 13C is rapidly released from methane clathrates3. Assuming that variations of the marine 13C/12C ratio are directly recorded in carbonate rocks, thousands of carbon isotope analyses of late Precambrian examples have been published to correlate these otherwise undatable strata and to document perturbations to the carbon cycle just before the great expansion of metazoan life. Low 13C/12C in some Neoproterozoic carbonates is considered evidence of carbon cycle perturbations unique to the Precambrian. These include complete oxidation of all organic matter in the ocean2 and complete produc- tivity collapse such that low-13C/12C hydrothermal CO2 becomes the main input of carbon4. Here we compile all published oxygen and carbon isotope data for Neoproterozoic marine carbonates, and consider them in terms of processes known to alter the isotopic composition during transformation of the initial precipitate into limestone/dolostone. We show that the combined oxygen and carbon isotope systematics are identical to those of well- understood Phanerozoic examples that lithified in coastal pore fluids, receiving a large groundwater influx of photosynthetic carbon from terrestrial phytomass. Rather than being perturba- tions to the carbon cycle, widely reported decreases in 13C/12C in Neoproterozoic carbonates are more easily interpreted in the same way as is done for Phanerozoic examples. This influx of terrestrial carbon is not apparent in carbonates older than 850 Myr, so we infer an explosion of photosynthesizing communities on late Precambrian land surfaces. As a result, biotically enhanced weathering generated carbon-bearing soils on a large scale and their detrital sedimentation sequestered carbon 5. This facilitated a rise in O2 necessary for the expansion of multicellular life.
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The Latest on Volcanic Eruptions and Climate
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2nd paragraph: It is well known that large volcanic eruptions inject sulfur gases into the stratosphere, which convert to sulfate aerosols with a life- time of several months to about 2 years. The radiative effects of these aerosol clouds produce global cooling and are an important natural cause of climate change. Regional responses include winter warming of Northern Hemisphere continents and weakening of summer Asian and African monsoons. Even though there has not been a large eruption since the eruption of Mount Pinatubo in the Philippines on 15 June 1991, research contin- ues to produce interesting results.
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The Literature Gateway
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The Literature Gateway Project
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Forest management affects wildlife habitat by altering the structure and composition of vegetation communities. Every wildlife species uses a specific set of resources associated with different species and ages of forest trees (e.g., nesting cavities, den sites, acorn crops, fruit resources) to survive and reproduce. Forest managers, wildlife conservation groups, policy makers, and other stakeholders often need to review the literature on forest bird-vegetation relationships to inform decisions on natural resource management or ecosystem restoration. The literature gateway facilitates the exploration of this literature, helping users find references on a diverse range of management-relevant topics that have been compiled by subject experts based on searches of >60 different sources spanning the past 50+ years.
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The Literature Gateway Tool
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This tool allows users to search for literature on bird species-vegetation relationships in eastern and boreal forests of North America.
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The material footprint of nations
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Metrics on resource productivity currently used by governments suggest that some developed countries have increased the use of natural resources at a slower rate than economic growth (relative decoupling) or have even managed to use fewer resources over time (absolute decoupling). Using the material footprint (MF), a consumption-based indicator of resource use, we find the contrary: Achievements in decoupling in advanced economies are smaller than reported or even nonexistent. We present a time series analysis of the MF of 186 countries and identify material flows associated with global production and consumption networks in unprecedented specificity. By calculating raw material equivalents of international trade, we demonstrate that countries’ use of nondomestic resources is, on average, about threefold larger than the physical quantity of traded goods. As wealth grows, countries tend to reduce their domestic portion of materials extraction through international trade, whereas the overall mass of material consumption generally increases. With every 10% increase in gross domestic product, the average national MF increases by 6%. Our findings call into question the sole use of current resource productivity indicators in policy making and suggest the necessity of an additional focus on consumption- based accounting for natural resource use.
raw material consumption | multiregion input–output analysis | sustainable resource management
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The millennial atmospheric lifetime of anthropogenic CO2
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The notion is pervasive in the climate science community and in the public at large that the climate impacts of fossil fuel CO2 release will only persist for a few centuries. This conclusion has no basis in theory or models of the atmosphere/ocean carbon cycle, which we review here. The largest fraction of the CO2 recovery will take place on time scales of centuries, as CO2 invades the ocean, but a significant fraction of the fossil fuel CO2, ranging in published models in the literature from 20–60%, remains airborne for a thousand years or longer. Ultimate recovery takes place on time scales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste. The glacial/interglacial climate cycles demonstrate that ice sheets and sea level respond dramatically to millennial-timescale changes in climate forcing. There are also potential positive feedbacks in the carbon cycle, including methane hydrates in the ocean, and peat frozen in permafrost, that are most sensitive to the long tail of the fossil fuel CO2 in the atmosphere.
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The movement ecology and dynamics of plant communities in fragmented landscapes
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A conceptual model of movement ecology has recently been advanced to explain all movement by considering the interaction of four elements: internal state, motion capacity, navigation capacities, and external factors. We modified this framework to generate predictions for species richness dynamics of fragmented plant communities and tested them in experimental landscapes across a 7-year time series. We found that two external factors, dispersal vectors and habitat features, affected species coloniza- tion and recolonization in habitat fragments and their effects varied and depended on motion capacity. Bird-dispersed species richness showed connectivity effects that reached an asymptote over time, but no edge effects, whereas wind-dispersed species richness showed steadily accumulating edge and connectivity effects, with no indication of an asymptote. Unassisted species also showed increasing differences caused by connectivity over time, whereas edges had no effect. Our limited use of proxies for movement ecology (e.g., dispersal mode as a proxy for motion capacity) resulted in moderate predictive power for communities and, in some cases, highlighted the importance of a more complete understanding of movement ecology for predicting how landscape conservation actions affect plant community dynamics.
corridors dispersal diversity life-history traits species richness
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The Myth of Smart Growth
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“Smart growth” is an urban growth management strategy that applies planning and design principles intended to mitigate the impacts of continued growth. If properly applied, these principles represent a positive contribution to new urban development. However, the rhetoric of “smart growth” is that population levels and growth rates are not the problem; it’s merely a matter of how we grow. According to the “smart growth” program, if we are less wasteful and more efficient in our urban growth, we can keep growing and everything will work out fine. The “smart growth” approach is fundamentally pro-growth and does not envision an end to growth or a need to end growth.
“Smart growth” is cast as a comprehensive solution, whereas it is merely a potential means of modestly reducing the environmental, social, and economic impacts of continued growth while failing to address its inevitable consequences. The “smart growth” formula has been used to discount and transform legitimate public concerns about the amount and pace of growth into a discussion about how we should best continue growing.
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