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Allowable carbon emissions lowered by multiple climate targets
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Climate targets are designed to inform policies that would limit the
magnitude and impacts of climate change caused by anthropogenic
emissions of greenhouse gases and other substances. The target
that is currently recognized by most world governments1 places a
limit of two degrees Celsius on the global mean warming since
preindustrial times. This would require large sustained reductions
in carbon dioxide emissions during the twenty-first century and
beyond2–4. Such a global temperature target, however, is not sufficient
to control many other quantities, such as transient sea level
rise5
, ocean acidification6,7 and net primary production on land8,9.
Here, using an Earth system model of intermediate complexity
(EMIC) in an observation-informed Bayesian approach, we show
that allowable carbon emissions are substantially reduced whenmultiple
climate targets are set. We take into account uncertainties in
physical and carbon cycle model parameters, radiative efficiencies10,
climate sensitivity11 and carbon cycle feedbacks12,13 along with a
large set of observational constraints. Within this framework, we
explore a broad range of economically feasible greenhouse gas scenarios
from the integrated assessment community14–17 to determine
the likelihood of meeting a combination of specific global
and regional targets under various assumptions. For any given
likelihood of meeting a set of such targets, the allowable cumulative
emissions are greatly reduced from those inferred from the temperature
target alone. Therefore, temperature targets alone are unable
to comprehensively limit the risks from anthropogenic emissions.
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Managing Forests and Fire in Changing Climates
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With projected climate change, we
expect to face much more forest
fi re in the coming decades. Policymakers
are challenged not to categorize all
fires as destructive to ecosystems simply
because they have long fl ame lengths and kill
most of the trees within the fi re boundary. Ecological
context matters: In some ecosystems,
high-severity regimes are appropriate, but climate
change may modify these fi re regimes
and ecosystems as well. Some undesirable
impacts may be avoided or reduced through
global strategies, as well as distinct strategies
based on a forest’s historical fi re regime.
SCIENCE VOL 342 4 OCTOBER 2013
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Rate of tree carbon accumulation increases continuously with tree size
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Forests are major components of the global carbon cycle, providing
substantial feedback to atmospheric greenhouse gas concentrations1
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Our ability to understand and predict changes in the forest carbon
cycle—particularly net primary productivity and carbon storage—
increasingly relies on models that represent biological processes
across several scales of biological organization, from tree leaves to
forest stands2,3. Yet, despite advances in our understanding of productivity
at the scales of leaves and stands, no consensus exists about
the nature of productivity at the scale of the individual tree4–7, in
part because we lack a broad empirical assessment of whether rates
of absolute treemass growth (and thus carbon accumulation) decrease,
remain constant, or increase as trees increase in size and age. Here we
present a global analysis of 403 tropical and temperate tree species,
showing that for most species mass growth rate increases continuously
with tree size. Thus, large, old trees do not act simply as senescent
carbon reservoirs but actively fix large amounts of carbon
compared to smaller trees; at the extreme, a single big tree can add
the same amount of carbon to the forest within a year as is contained
in an entire mid-sized tree. The apparent paradoxes of individual
tree growth increasing with tree size despite declining leaf-level8–10
and stand-level10 productivity can be explained, respectively, by
increases in a tree’s total leaf area that outpace declines in productivity
per unit of leaf area and, among other factors, age-related
reductions in population density. Our results resolve conflicting
assumptions about the nature of tree growth,inform efforts to undertand
and model forest carbon dynamics, and have additional implications
for theories of resource allocation11 and plant senescence1
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Risk Communication on Climate: Mental Models and Mass Balance
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Public confusion about the urgency of reductions
in greenhouse gas emissions results from a basic
misconception.
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When the river runs dry: human and ecological values of dry riverbeds
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Temporary rivers and streams that naturally cease to flow and dry up can be found on every continent.
Many other water courses that were once perennial now also have temporary flow regimes due to the effects
of water extraction for human use or as a result of changes in land use and climate. The dry beds of these
temporary rivers are an integral part of river landscapes. We discuss their importance in human culture and
their unique diversity of aquatic, amphibious, and terrestrial biota. We also describe their role as seed and
egg banks for aquatic biota, as dispersal corridors and temporal ecotones linking wet and dry phases, and as
sites for the storage and processing of organic matter and nutrients. In light of these valuable functions, dry
riverbeds need to be fully integrated into river management policies and monitoring programs. We also
identify key knowledge gaps and suggest research questions concerning the values of dry riverbeds.
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The energetic implications of curtailing versus storing solar- and wind-generated electricity
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We present a theoretical framework to calculate how storage affects the energy return on energy
investment (EROI) ratios of wind and solar resources. Our methods identify conditions under which it is
more energetically favorable to store energy than it is to simply curtail electricity production.
Electrochemically based storage technologies result in much smaller EROI ratios than large-scale
geologically based storage technologies like compressed air energy storage (CAES) and pumped
hydroelectric storage (PHS). All storage technologies paired with solar photovoltaic (PV) generation yield
EROI ratios that are greater than curtailment. Due to their low energy stored on electrical energy
invested (ESOIe) ratios, conventional battery technologies reduce the EROI ratios of wind generation
below curtailment EROI ratios. To yield a greater net energy return than curtailment, battery storage
technologies paired with wind generation need an ESOIe > 80. We identify improvements in cycle life as
the most feasible way to increase battery ESOIe. Depending upon the battery's embodied energy
requirement, an increase of cycle life to 10 000–18 000 (2–20 times present values) is required for
pairing with wind (assuming liberal round-trip efficiency [90%] and liberal depth-of-discharge [80%]
values). Reducing embodied energy costs, increasing efficiency and increasing depth of discharge will
also further improve the energetic performance of batteries. While this paper focuses on only one
benefit of energy storage, the value of not curtailing electricity generation during periods of excess
production, similar analyses could be used to draw conclusions about other benefits as well
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Ecologists Report Huge Storm Losses in China’s Forests
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From delicate orchids and magnolias to rare Chinese yews and Kwangtung pines, the flora of Guangdong
Nanling National Nature Reserve is considered so precious that ecologists call the reserve “a treasure trove of species.” But winter storms have reduced the biological hot spot to a splintered ruin. Snow, sleet, and ice laid waste to 90% of the 58,000- hectare reserve’s forests, says He Kejun, director of Guangdong Forestry
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Challenges in the conservation, rehabilitation and recovery of native stream salmonid populations: beyond the 2010 Luarca symposium
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– In May 2010, I chaired a session on challenges to salmonid conservation at the international symposium
‘Advances in the population ecology of stream salmonids’ in Luarca, Spain. I suggested that in addition to scientific challenges, a major challenge will be improving the links between ecologists, conservationists and policy makers. Because the Luarca symposium focused mainly on ecological research, little time was explicitly devoted to conservation. My objective in this paper is to further discuss the role of ecological research in informing salmonid conservation. I begin with a brief overview of research highlights from the symposium. I then use selected examples to show that ecological research has already contributed much towards informing salmonid conservation, but that ecologists will always be faced with limitations in their predictive ability. I suggest that conservation will need to move forward regardless of these limitations, and I call attention to some recent efforts wherein ecological research has played a crucial role. I conclude that ecologists should take urgent action to ensure that their results are availableto inform resource managers, conservation organisations and policy makers regarding past losses and present threats to native, locally-adapted salmonid stocks.
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Climate change impacts on the biophysics and economics of world fisheries
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Global marine fisheries are underperforming economically because of overfishing, pollution and habitat degradation. Added to these threats is the looming challenge of climate change. Observations, experiments and simulation models show that climate change would result in changes in primary productivity, shifts in distribution and changes in the potential yield of exploited marine species, resulting in impacts on the economics of fisheries worldwide. Despite the gaps in understanding climate change effects on fisheries, there is sufficient scientific information that highlights the need to implement climate change mitigation
and adaptation policies to minimize impacts on fisheries.
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Dissecting insect responses to climate warming: overwintering and post-diapause performance in the southern green stink bug, Nezara viridula, under simulated climate-change conditions
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The effect of simulated climate change on overwintering and postdiapause
reproductive performance is studied in Nezara viridula (L.) (Heteroptera:
Pentatomidae) close to the species’ northern range limit in Japan. Insects are reared
from October to June under quasi-natural (i.e. ambient outdoor) conditions and in
a transparent incubator, in which climate warming is simulated by adding 2.5 ◦
C to
the ambient temperatures. Despite the earlier assumption that females of N. viridula
overwinter in diapause, whereas males do so in quiescence, regular dissections show
that the two sexes overwinter in a state of true diapause. During winter, both sexes are
dark-coloured and have undeveloped reproductive organs. Resumption of development
does not start until late March. During winter, the effect of simulated warming on the
dynamics and timing of physiological processes appears to be limited. However, the
warming significantly enhances winter survival (from 27–31% to 47–70%), which
is a key factor in range expansion of N. viridula. In spring, the effect of simulated
warming is complex. It advances the post-diapause colour change and transition from
dormancy to reproduction. The earlier resumption of development is more pronounced
in females: in April, significantly more females are already in a reproductive state
under the simulated warming than under quasi-natural conditions. In males, the
tendency is similar, although the difference is not significant. Warming significantly
enhances spring survival and percentage of copulating adults, although not the percentage
of ovipositing females and fecundity. The results suggest that, under the expected
climate-warming conditions, N. viridula will likely benefit mostly as a result of
increased winter and spring survival and advanced post-diapause reproduction. Further
warming is likely to allow more adults to survive the critical cold season and contribute
(both numerically and by increasing heterogeneity) to the post-overwintering population
growth, thus promoting the establishment of this species in newly-colonized
area
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