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Freshwater Methane Emissions Offset the Continental Carbon Sink
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Acornerstone of our understanding of the
contemporary global carbon cycle is that
the terrestrial land surface is an important
greenhouse gas (GHG) sink (1, 2). The global
land sink is estimated to be 2.6 T 1.7 Pg of C
year−1 (variability T range, excluding C emissions
because of deforestation) (1). Lakes, impoundments,
and rivers are parts of the terrestrial landscape,
but they have not yet been included in the
terrestrial GHG balance (3, 4). Available data
suggest, however, that freshwaters can be substantial
sources of CO2 (3, 5) and CH4 (6). Over time,
soil carbon reaches freshwaters by lateral hydrological
transport, where it can meet several fates,
including burial in sediments, further transport to
the sea, or evasion to the atmosphere as CO2 or
CH4 (7). CH4 emissions may be small in terms of
carbon, but CH4 is a more potent GHG than CO2
over century time scales. This study indicates that
global CH4 emissions expressed as CO2 equivalents
correspond to at least 25% of the estimated
terrestrial GHG sink.
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Not All About Consumption
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Resource exploitation can lead to increased
ecological impacts even when overall
consumption levels stay the same
15 March 2013 VOL 339 SCIENCE
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Defaunation in the Anthropocene
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We live amid a global wave of anthropogenically driven biodiversity loss: species
and population extirpations and, critically, declines in local species abundance.
Particularly, human impacts on animal biodiversity are an under-recognized form of
global environmental change. Among terrestrial vertebrates, 322 species have
become extinct since 1500, and populations of the remaining species show 25%
average decline in abundance. Invertebrate patterns are equally dire: 67% of
monitored populations show 45% mean abundance decline. Such animal declines
will cascade onto ecosystem functioning and human well-being. Much remains unknown
about this “Anthropocene defaunation”; these knowledge gaps hinder our capacity
to predict and limit defaunation impacts. Clearly, however, defaunation is both a
pervasive component of the planet’s sixth mass extinction and also a major driver of
global ecological change
25 JULY 2014 • VOL 345 ISSUE 6195
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How Does Climate Change Affect Biodiversity?
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The most recent and complex bioclimate
models excel at describing species’ current
distributions. Yet, it is unclear which models
will best predict how climate change will affect
their future distributions.
8 SEPTEMBER 2006 VOL 313 SCIENCE
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Changes in Climatic Water Balance Drive Downhill Shifts in Plant Species’ Optimum Elevations
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Uphill shifts of species’ distributions in response to historical warming are well documented, which leads
to widespread expectations of continued uphill shifts under future warming. Conversely, downhill shifts
are often considered anomalous and unrelated to climate change. By comparing the altitudinal
distributions of 64 plant species between the 1930s and the present day within California, we show that
climate changes have resulted in a significant downward shift in species’ optimum elevations. This
downhill shift is counter to what would be expected given 20th-century warming but is readily
explained by species’ niche tracking of regional changes in climatic water balance rather than
temperature. Similar downhill shifts can be expected to occur where future climate change scenarios
project increases in water availability that outpace evaporative demand.
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The Greening of Synfuels
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An old, dirty technology to make transportation fuels from coal could
fight global warming, say proponents. The trick is using more biomass
and burying the carbon dioxide that’s generated
18 APRIL 2008 VOL 320 SCIENCE
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All Downhill From Here?
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Biologists say climate change may already be affecting high-mountain ecosystems around the world, where plants and animals adapted to cold, barren conditions now face higher temperatures and a surge of predators and competitors
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Human Evolution Out of Africa: The Role of Refugia and Climate Change
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Although an African origin of the modern human species is generally accepted, the evolutionary
processes involved in the speciation, geographical spread, and eventual extinction of archaic
humans outside of Africa are much debated. An additional complexity has been the recent evidence
of limited interbreeding between modern humans and the Neandertals and Denisovans. Modern
human migrations and interactions began during the buildup to the Last Glacial Maximum,
starting about 100,000 years ago. By examining the history of other organisms through glacial
cycles, valuable models for evolutionary biogeography can be formulated. According to one
such model, the adoption of a new refugium by a subgroup of a species may lead to important
evolutionary changes.
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Rescuing Wolves from Politics: Wildlife as a Public Trust Resource
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Long-term conservation of gray wolves is
possible if states recognize a legal obligation
to conserve species as a public trust resource
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Rapid Range Shifts of Species Associated with High Levels of Climate Warming
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The distributions of many terrestrial organisms are currently shifting in latitude or elevation in responseto changing climate. Using a meta-analysis, we estimated that the distributions of species haverecently shifted to higher elevations at a median rate of 11.0 meters per decade, and to higher latitudes
at a median rate of 16.9 kilometers per decade. These rates are approximately two and three times faster than previously reported. The distances moved by species are greatest in studies showing thehighest levels of warming, with average latitudinal shifts being generally sufficient to track temperature
changes. However, individual species vary greatly in their rates of change, suggesting that the range shift of each species depends on multiple internal species traits and external drivers of change. Rapid average shifts derive from a wide diversity of responses by individual species.
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