HAZARDS OF TEMPERATURE ON FOOD AVAILABILITY IN CHANGING ENVIRONMENTS
Description: Global
temperatures are predicted to increase from rising
levels of atmospheric carbon dioxide (CO2) and other greenhouse
gases. We conducted experiments in sunlit, controlled-environment chambers and
temperature-gradient greenhouses to determine effects of elevated temperature
and doubled CO2 concentration on pollination and yield of rice,
soybean, dry bean, peanut, and grain sorghum. Photosynthesis and vegetative
growth were more tolerant of increasing temperatures than reproductive
processes. Rice seed yields were optimum at 25°C mean daily temperature and
decreased with increasing temperature (typically about 10% decline for each 1°C
rise in temperature). Grain sorghum yield response to temperature was similar to
rice, but dry bean was more sensitive, and soybean and peanut were more
tolerant. Pollen viability followed a temperature response similar to seed
yield. Comparisons of 43 rice cultivars in temperature-gradient greenhouses
showed genetic variation in percent seed-set in response to a 4.5°C increase
above ambient temperatures in Florida.
Thus, there appears to be a range of adaptation of seed crops to temperature.
Elevated CO2 did not prevent high temperature decline in yield; in
dry bean it made pollination more sensitive to high temperature. In summary, global
warming will be a greater threat to crop seed yields than to photosynthesis and
vegetative growth. However, crop genetic improvements might ameliorate part,
but not all, of the high temperature hazards for seed yields and global food
security.
Author's Names: L.H. Allen, Jr, K.J. Boote, P.V.V. Prasad, J.M.G. Thomas, and J.C.V. Vu
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GREENHOUSE GAS CO2, CH4 AND CLIMATE EVOLUTION SINCE 650KYRS DEDUCED FROM ANTARCTIC ICE CORES
Description: Ice cores are unique archives of past climatic and atmospheric
conditions through the isotopic composition of the ice and the analysis of the
air bubbles trapped. In 1999 Petit et al published the reconstruction of the
Antarctic climate and atmospheric composition over the last 420 000 years from
the Vostok ice core. This record covered the last four glacial inter glacial
cycles back to the end of the marine interstadial 11 (MIS 11). It has revealed
the close relationship between the atmospheric part of the carbon cycle and the
climate. With CO2 concentration oscillating between 180 and 280 ppmv
during the last 4 climatic cycles. In
a similar way the methane concentration followed closely
temperature on glacial interglacial time scales, with millennial-scale
structures during glacial times which appear out of phased with Antarctic
temperature but, at least for the last glaciation, in phase with the Greenland rapid climatic oscillations, as revealed by the
GISP and GRIP ice cores.
Author's Names: J.M. Barnola, U. Siegenthaler, et al
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BIOGEOCHEMICAL CHANGES IN SUBTROPICAL AND SUBPOLAR MODE WATERS: A MINER’S CANARY FOR CLIMATE ...
Description: Long-term observations of carbon, nutrients and oxygen
in upper thermocline waters, such as subtropical and subpolar mode waters, have
revealed substantial interannual to decadal variations. While part of this
variability can be ascribed to internal ocean and ecosystem dynamics as well as
large-scale climate phenomena (like ENSO,
NAO or the PDO), we presently do not know to which extent this variability is
influenced by anthropogenic climate change. As a first step to answer this
detection question, the impact of natural variability on biogeochemical
properties in thermocline waters must be understood and quantified. This
permits us then to accurately describe the natural "noise" against
which an anthropogenic change needs to be detected. Subtropical and subpolar
mode waters may be ideally suited to look at this task since they tend to
respond sensitively to climate variations, integrate short-time scale
variations over time, and hence exhibit maximum signal to noise ratio. We investigate the role of mode water
formation and spreading on interannual to decadal accumulation and release of
nutrients and carbon by analyzing results from model runs with the Upper Ocean
Model [Danabasoglu and McWilliams 2000] coupled
to the ecosystem model of Moore et al.
[2002]. We compare results from a run forced with NCEP reanalysis data for the
period from 1948 to present with a climatological control run. To better
isolate the mechanisms forcing these biogeochemical changes, we compare our
results also to a set of experiments in which we manipulate the wind stress
forcing and sea surface temperature fields of the model locally.
Author's Names: H. Brix and N. Gruber
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THE EXPRESSION OF BIOSPHERE RESPONSE TO LIGHT LEVEL CHANGES ON 18O OF ATMOSPHERIC CO2
Description: Observations
suggest the global reflectivity of Earth changed during recent decades. Although there is some ambiguity surrounding
these findings, it is clear that, should there be changes in clouds or
scattering aerosols, a change in the total solar radiation received at the
surface and the fraction of diffuse light could result. Intriguingly, the d18O of CO2
time series measured at Mauna Loa shows variability
during the 1990s that does not match secular trends in CO2
concentration or d13C. While a decrease in total solar radiation
alone would reduce biospheric productivity, an increase in diffuse light can
increase productivity, as has been argued for the period following the eruption
of Pinatubo. Moreover, since the changes in radiation affect the surface latent
energy exchange, the isotopic composition of terrestrial water with which CO2
interacts (specifically leaf and soil water) will be modified and can thus
drive a change in isotopic fluxes.
Author's Names: N. Buenning, D. Noone, C. Still, W. Riley, et al
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NEW COUPLED CLIMATE-CARBON SIMULATIONS WITH THE IPSL MODEL: FROM VALIDATION WITH ATMOSPHERIC ...
Description: We have developed a
Climate-Carbon coupled model based on the IPSL OAGCM and on two biogeochemical
models, ORCHIDEE for the continent and PISCES for the ocean, to investigate the
coupling between climate change and the global carbon cycle. We have performed
four climate-carbon simulations over the 1860-2100 period in which atmospheric
CO2 is interactively calculated. They are :
§
A control coupled
simulation with no anthropogenic emissions.
§
A coupled
simulation with anthropogenic emissions.
§
A coupled
simulation with anthropogenic emissions including non-CO2 greenhouse
and sulfate aerosols.
§
An uncoupled
carbon simulation with the same anthropogenic emissions as second simulation
but for which atmospheric CO2 change has no impact on climate.
Compared to the first IPSL
Climate-Carbon coupled model [Dufresne,
et al., 2002], the simple carbon models have been replaced by IPSL advanced
ocean and land biogeochemical models, respectively PISCES and ORCHIDEE. CO2
is transported in the atmosphere and compared with observations. Comparison
with satellite data is also done. We then analyze the coupled and uncoupled
simulations, highlight the importance of the climate change both on the oceanic
and biosphere sink and estimate the climate-carbon feedback. The results are
also compared to the outputs of other models participating in the C4MIP
inter-comparison project. Finally, off-line simulations are carried out to
perform sensitivity tests (fire, dynamics of land and ocean ecosystems, soil
respiration) in order to identify the key processes which govern the simulated
response.
Author's Names: P. Cadule, P. Friedlingstein and L. Bopp
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PERSISTENCE OF NITROGEN LIMITATION OVER TERRESTRIAL CARBON UPTAKE
Description: Because
vegetation growth in the Northern Hemisphere is typically nitrogen-limited,
increased nitrogen deposition could have attenuating effect on rising
atmospheric CO2 by stimulating the accumulation of biomass. Given
the high carbon to nitrogen ratios and long lifetimes of carbon in wood, a most
significant effect of nitrogen fertilization is expected in forests. Forest
inventories indicate that the carbon content of northern forests have increased
concurrently with increased nitrogen deposition since the 1950s [Spiecker et al.,
1996]. In addition, variations in atmospheric CO2 indicate a
globally significant carbon sink in northern mid-latitude forest regions [Schimel et al.,
2001]. It is unclear however, whether elevated nitrogen deposition or other
factors are the primary cause of carbon sequestration in northern forests. We
argue that the elevated nitrogen deposition is unlikely to enhance vegetation
carbon sink significantly because of its differentiating effect on the carbon
sequestration capacity of uneven aged forests and climatic limitations on
carbon sequestration in the Northern Hemisphere. We estimate the potential of
forests with lifted nitrogen limitation to decelerate CO2
concentrations rise in the atmosphere and therefore to mitigate climate
warming. We also outline areas of the Northern Hemisphere which are most
sensitive to increased nitrogen deposition.
Author's Names: G. Churkina, M. Vetter, and K. Trusilova
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EUROPEAN-WIDE REDUCTION IN PRIMARY PRODUCTIVITY CAUSED BY THE HEAT AND DROUGHT IN 2003
Description:
Future climate warming is expected to enhance plant
growth in temperate ecosystems and to increase carbon sequestration. But
although severe regional heatwaves may become more frequent in a changing
climate, and their impact on terrestrial carbon cycling is unclear. Europe experienced a particularly extreme climate anomaly
during 2003, with July temperatures up to 6°C above long-term means, and annual
precipitation deficits up to 300 mmy-1, that is 50% below the
average. We used the 2003 heatwave as a ‘laboratory assistant’ to estimate the
impact on terrestrial carbon cycling.
Author's Names: Ph. Ciais, M. Reichstein, N. Viovy, A. Granier, et al
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SIMULATION OF THE RESPONSE OF NORTHEAST SIBERIA PERMAFROST CARBON STOCK TO THE GLOBAL WARMING
Description:
The
Siberian permafrost carbon stock has been studied using a newly developed soil
model, which takes into account soil freezing/thawing and organic matter
decomposition in the form of soil respiration and methanogenesis. The results show that the soil
response to a rapid external warming can be a self-sustaining process involving
permafrost melting, deep-soil
respiration with associated heat generation,
and methanogenesis. Most of the soil carbon is thus consumed until there is not
enough of it to feed intense respiration and/or methanogenesis. This behavior
is manifested only at sufficiently warm climate established after the warming.
Carbon consumption in the extremely carbon-rich
Yedoma Ice Complex region appears to be moderate due to cold climatic
conditions.
Author's Names: D.V. Khvorostyanov, G. Krinner, P. Ciais, et al
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MAN-INDUCED CHANGES IN C STORAGE DURING THE 20TH CENTURY: ENVIRONMENTAL AND GEOCHEMICAL RECORD
Description:
Despite
their relative small extension, wetlands are important as sources or sinks of
C. But, due to their intermediate position between land and permanent water,
they have been modified in the name of “health” or “productivity.” Such changes
have altered substantially their ability to store/produce C greenhouse gasses
but the main point is to establish until which point this changes are
“structural” (implying the intrinsic environmental mechanisms), and therefore
unrecoverable, or “casual” (implying not the environment processes but its
“external”–not directly implied in the C storage/emission- components), and
consequently recoverable. Temperate wetlands are strongly dependant on water
availability due to their position but, on the other hand, use to be occupied
by resistant species able to survive hard conditions. The example shown below
presents a case of intense human activity on a Mediterranean wetland that has
caused very intense changes in the flooded area but not so evident and
perdurable in the main ecological relations implied in the C cycle.
Author's Names: F. Dominguez-Castro, J.I. Santisteban, R. Mediavilla, et al
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CARBON-CLIMATE SYSTEM FEEDBACKS TO NATURAL AND ANTHROPOGENIC CLIMATE CHANGE
Description:
A new three-dimensional global coupled carbon-climate model is
presented in the framework of the Community Climate System Model (CSM-1.4). A
1000-year control simulation has stable global annual mean surface temperature
and atmospheric CO2 with no flux adjustment in either physics or
biogeochemistry. At low frequencies (timescale > 20 years), the ocean tends
to damp (20-25%) slow, natural variations in atmospheric CO2
generated by the terrestrial biosphere. Transient experiments
(1820-2100) show that carbon sink strengths are inversely related to the rate
of fossil fuel emissions, so that carbon storage capacities of the land and
oceans decrease and climate warming accelerates with faster CO2
emissions. There is a positive feedback between the carbon and climate systems,
so that climate warming acts to increase the airborne fraction of anthropogenic
CO2 and amplify the climate change itself. Globally, the
amplification is small at the end of the 21st century in our model because of
its low transient climate response and the near-cancellation between large
regional changes in the hydrologic and ecosystem responses.
Author's Names: S.C. Doney. K. Lindsay, I. Fung, and J. John
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