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Missing feedbacks, asymmetric uncertainties, and the underestimation of future warming
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Historical evidence shows that atmospheric greenhouse
gas (GhG) concentrations increase during periods of
warming, implying a positive feedback to future climate
change. We quantified this feedback for CO2 and CH4 by
combining the mathematics of feedback with empirical icecore
information and general circulation model (GCM)
climate sensitivity, finding that the warming of 1.5 –4.5C
associated with anthropogenic doubling of CO2 is amplified
to 1.6– 6.0C warming, with the uncertainty range deriving
from GCM simulations and paleo temperature records.
Thus, anthropogenic emissions result in higher final GhG
concentrations, and therefore more warming, than would be
predicted in the absence of this feedback. Moreover, a
symmetrical uncertainty in any component of feedback,
whether positive or negative, produces an asymmetrical
distribution of expected temperatures skewed toward higher
temperature. For both reasons, the omission of key positive
feedbacks and asymmetrical uncertainty from feedbacks, it
is likely that the future will be hotter than we think.
Citation: Torn, M. S., and J. Harte (2006), Missing feedbacks,
asymmetric uncertainties, and the underestimation of future
warming.
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TRY – a global database of plant traits
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Plant traits – the morphological, anatomical, physiological, biochemical and phenological characteristics of plants and
their organs – determine how primary producers respond to environmental factors, affect other trophic levels,
influence ecosystem processes and services and provide a link from species richness to ecosystem functional diversity.
Trait data thus represent the raw material for a wide range of research from evolutionary biology, community and
functional ecology to biogeography. Here we present the global database initiative named TRY, which has united a
wide range of the plant trait research community worldwide and gained an unprecedented buy-in of trait data: so far
93 trait databases have been contributed. The data repository currently contains almost three million trait entries for
69 000 out of the world’s 300 000 plant species, with a focus on 52 groups of traits characterizing the vegetative and
regeneration stages of the plant life cycle, including growth, dispersal, establishment and persistence. A first data
analysis shows that most plant traits are approximately log-normally distributed, with widely differing ranges of
variation across traits. Most trait variation is between species (interspecific), but significant intraspecific variation is
also documented, up to 40% of the overall variation. Plant functional types (PFTs), as commonly used in vegetation
models, capture a substantial fraction of the observed variation – but for several traits most variation occurs within
PFTs, up to 75% of the overall variation. In the context of vegetation models these traits would better be represented by
state variables rather than fixed parameter values. The improved availability of plant trait data in the unified global
database is expected to support a paradigm shift from species to trait-based ecology, offer new opportunities for
synthetic plant trait research and enable a more realistic and empirically grounded representation of terrestrial
vegetation in Earth system models.
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U.S. Forest Carbon and Climate Change Controversies and Win-Win Policy Approaches
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As consensus grows about the serious impacts of global climate change, the role of
forests in carbon storage is increasingly recognized. Terrestrial vegetation worldwide
currently removes about 24 percent of the greenhouse gases released by industrial
processes. Unfortunately, this contribution is approximately cancelled out by carbon
released as a result of global deforestation and other ecosystem changes. Slowing or
halting the rate of deforestation is thus one of the prime strategies to mitigate global
climate change.
The U.S. situation differs from the global one in several ways. Since both forest acres
and average biomass per forest acre are currently increasing, as U.S. forests recover
from past clearing or heavy harvest, our forest carbon stores are growing larger over
time. However, our high rate of industrial emissions means that only about 10 percent
of the carbon released from burning fossil fuels in the United States is captured by our
forests. Moreover, net U.S. forest carbon sequestration has begun to slow in recent
years as reforestation reaches its limits and development sprawls into more rural forested
areas. U.S. forests could possibly capture a much higher portion of our industrial
emissions, but only if we prevent forest conversion and development and manage our
forests to maximize carbon stores.
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Unburnable Carbon – Are the world’s financial markets carrying a carbon bubble?
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The Carbon Tracker initiative is a new way of looking at the carbon emissions
problem. It is focused on the fossil fuel reserves held by publically listed
companies and the way they are valued and assessed by markets. Currently
financial markets have an unlimited capacity to treat fossil fuel reserves
as assets. As governments move to control carbon emissions, this market
failure is creating systemic risks for institutional investors, notably the
threat of fossil fuel assets becoming stranded as the shift to a low-carbon
economy accelerates.
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Scenario Planning: a Tool for Conservation in an Uncertain World
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: Conservation decisions about how, when, and where to act are typically based on our expectations
for the future. When the world is highly unpredictable and we are working from a limited range of expectations,
however, our expectations will frequently be proved wrong. Scenario planning offers a framework for
developing more resilient conservation policies when faced with uncontrollable, irreducible uncertainty. A
scenario in this context is an account of a plausible future. Scenario planning consists of using a few contrasting
scenarios to explore the uncertainty surrounding the future consequences of a decision. Ideally, scenarios
should be constructed by a diverse group of people for a single, stated purpose. Scenario planning can
incorporate a variety of quantitative and qualitative information in the decision-making process. Often, consideration
of this diverse information in a systemic way leads to better decisions. Furthermore, the participation
of a diverse group of people in a systemic process of collecting, discussing, and analyzing scenarios
builds shared understanding. The robustness provided by the consideration of multiple possible futures has
served several groups well; we present examples from business, government, and conservation planning that
illustrate the value of scenario planning. For conservation, major benefits of using scenario planning are (1)
increased understanding of key uncertainties, (2) incorporation of alternative perspectives into conservation
planning, and (3) greater resilience of decisions to surprise.
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Call Off the Quest
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Over the past 30 years, the climate research community has made valiant efforts to answer the “climate sensitivity” question: What is the long-term equilibrium warming response to a doubling of atmospheric carbon dioxide? Earlier this year, the Intergovernmental Panel on Climate Change (1) concluded that this sensitivity is likely to be in the range of 2° to 4.5°C, with a 1-in-3 chance that it is outside that range. The
lower bound of 2°C is slightly higher than the 1.6°C proposed in the 1970s (2).
26 OCTOBER 2007 VOL 318 SCIENCE
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Why Is Climate Sensitivity So Unpredictable?
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Uncertainties in projections of future climate change have not lessened substantially in past
decades. Both models and observations yield broad probability distributions for long-term
increases in global mean temperature expected from the doubling of atmospheric carbon dioxide,
with small but finite probabilities of very large increases. We show that the shape of these
probability distributions is an inevitable and general consequence of the nature of the climate
system, and we derive a simple analytic form for the shape that fits recent published distributions
very well. We show that the breadth of the distribution and, in particular, the probability of
large temperature increases are relatively insensitive to decreases in uncertainties associated with
the underlying climate processes.
VOL 318 26 OCTOBER 2007
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Volcanic cause of catastrophe
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From the timing, it looks as if an episode of marked oceanic oxygen
deficiency during the Cretaceous was the result of undersea volcanism.
Studies of such events are relevant to the warming world of today.
NATURE|Vol 454|17 July 2008
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Are we in the midst of the sixth mass extinction? A view from the world of amphibians
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Many scientists argue that we are either entering or in the midst
of the sixth great mass extinction. Intense human pressure, both
direct and indirect, is having profound effects on natural environments.
The amphibians—frogs, salamanders, and caecilians—may
be the only major group currently at risk globally. A detailed
worldwide assessment and subsequent updates show that onethird
or more of the 6,300 species are threatened with extinction.
This trend is likely to accelerate because most amphibians occur in
the tropics and have small geographic ranges that make them
susceptible to extinction. The increasing pressure from habitat
destruction and climate change is likely to have major impacts on
narrowly adapted and distributed species. We show that
salamanders on tropical mountains are particularly at risk. A new
and significant threat to amphibians is a virulent, emerging infectious
disease, chytridiomycosis, which appears to be globally
distributed, and its effects may be exacerbated by global warming.
This disease, which is caused by a fungal pathogen and implicated
in serious declines and extinctions of >200 species of amphibians,
poses the greatest threat to biodiversity of any known disease. Our
data for frogs in the Sierra Nevada of California show that the
fungus is having a devastating impact on native species, already
weakened by the effects of pollution and introduced predators. A
general message from amphibians is that we may have little time
to stave off a potential mass extinction.
11466–11473 PNAS August 12, 2008 vol. 105 suppl. 1
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Phylogenetic patterns of species loss in Thoreau’s woods are driven by climate change
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Climate change has led to major changes in the phenology (the
timing of seasonal activities, such as flowering) of some species but
not others. The extent to which flowering-time response to temperature
is shared among closely related species might have
important consequences for community-wide patterns of species
loss under rapid climate change. Henry David Thoreau initiated a
dataset of the Concord, Massachusetts, flora that spans !150 years
and provides information on changes in species abundance and
flowering time. When these data are analyzed in a phylogenetic
context, they indicate that change in abundance is strongly correlated
with flowering-time response. Species that do not respond to
temperature have decreased greatly in abundance, and include
among others anemones and buttercups [Ranunculaceae pro parte
(p.p.)], asters and campanulas (Asterales), bluets (Rubiaceae p.p.),
bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales),
mints (Lamiaceae p.p.), orchids (Orchidaceae), roses (Rosaceae
p.p.), saxifrages (Saxifragales), and violets (Malpighiales).
Because flowering-time response traits are shared among closely
related species, our findings suggest that climate change has
affected and will likely continue to shape the phylogenetically
biased pattern of species loss in Thoreau’s woods
PNAS ! November 4, 2008 ! vol. 105 ! no. 44 ! 17029–17033
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