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 | Hazards of Temperature on Food Availability in Changing Environments (HOT-FACE) |  |
 by Leon Allen Jr.
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.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 11:45:00 MDT (1010 reads)
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| The Amazon and the Modern Carbon Cycle | |
by Jean Pierre Ometto
Is
the massive Amazon forest a CO2 sink, a source or is it in
equilibrium?
There
is a large uncertainty in carbon fluxes estimates for the tropics as a whole
and in particular for the Amazon region in South America,
bringing the attention to the lack of information to call the region a carbon
source or sink. The production of scientific consistent and long term data
series for the region is a process that has to advance step by step.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 11:30:00 MDT (1036 reads)
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| New Coupled Climate-carbon Simulations from the IPSL Model | |
by Patricia Cadule
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 :
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A control coupled
simulation with no anthropogenic emissions.
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A coupled
simulation with anthropogenic emissions.
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A coupled
simulation with anthropogenic emissions including non-CO2 greenhouse
and sulfate aerosols.
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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.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 11:15:00 MDT (1043 reads)
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| The Changing Carbon Cycle | |
by Inez Fung
The carbon cycle has undergone
changes from 1998-2003 as a result of extensive droughts. The CO2 seasonal amplitude at MLO
halted its increase, and the CO2 growth rate accelerated as a result
of a slowing down of the North American carbon sink. In a series of coupled carbon-climate model
experiments, we show a greater probability of drier soils in the 21st
century, especially in the tropics and in mid-latitude summers as
temperature-driven evapotranspiration exceed precipitation, and a positive
feedback between the carbon cycle and climate. This positive feedback reduces
the land and ocean’s capacity to store fossil fuel CO2 and
accelerates the warming. A fossil fuel emission accelerating rapidly as the
sink capacities decrease leads to further increases in the airborne fraction of
fossil fuel CO2.
Link to Abstract
Updated! Link to Slides
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Posted by admin on Thursday, September 29 @ 11:00:00 MDT (1086 reads)
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| CO2 Uptake of the Marine Biosphere | |
By Arne Winguth
Different CO2 stabilization scenarios and CO2
emission scenarios have been carried out with an earth system model to
investigate feedbacks between future climate change and carbon cycle. The model
predicts a sensitivity of 1.6±0.1 K for an increase of 280 ppm in atmospheric
CO2 concentration. The decrease of the thermohaline circulation is
predominantly controlled by an enhanced atmospheric moisture transport to high
latitudes by global warming. Overall, the simulated effect of atmospheric CO2
concentration on climate change reduces the total carbon uptake of the ocean
and the land is reduced by 24-29%.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 10:30:00 MDT (1025 reads)
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| European-wide Reduction in Primary Productivity Caused by the Heat and Drought i | |
by Philippe Ciais
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.
Link to abstract
Link to slides
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Posted by admin on Thursday, September 29 @ 09:15:00 MDT (1354 reads)
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| Persistence of Nitrogen Limitation over Terrestrial Carbon Uptake | |
by Galina Churkina
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.
Link to abstract
Link to slides
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Posted by admin on Thursday, September 29 @ 09:00:00 MDT (1050 reads)
(Read More... | 1 comment)
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| Atmospheric CO2, Carbon Isotopes, the Sun, and Climate Change over the Last Mill | |
By Fortunat Joos
The records of atmospheric CO2 and of NH surface temperature
covering the past millennium hold information on the strength of the
sensitivity of the global carbon cycle to climate changes. This sensitivity is
defined as the change in atmospheric CO2 in response to a given
change in NH temperature in units of ppm K-1. The magnitude of the
sensitivity is estimated for modest (< 1 K) temperature variations from
simulations with the Bern Carbon Cycle Climate model driven with solar and
volcanic forcing over the last millennium and from simulations with the range
of C4MIP models over the industrial periods. The model results are broadly
compatible with the data-deduced range.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 08:45:00 MDT (1144 reads)
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| Proposing a Mechanistic Understanding of Atmospheric CO2 During the late Pleist | |
By Peter Koehler
Paleo-climate records in ice cores revealed high
variability in temperature, atmospheric dust content and carbon dioxide. The
longest CO2 record from the Antarctic ice core of the Vostok station
went back in time as far as about 410 kyr BP showing a switch of glacials and
interglacials in all those parameters approximately every 100 kyr during the
last four glacial cycles with CO2 varying between 180-300 ppmv [Petit et al., 1999]. New measurements of dust and the
isotopic temperature proxy deuterium of the EPICA Dome C (EDC) ice core covered
the last 740 kyr, however, revealed glacial cycles of reduced temperature
amplitude [EPICA community members, 2004]. These
new archives offer the possibility to propose atmospheric CO2 for
the pre-Vostok time span as called for in the EPICA challenge [Wolff et al., 2004]. Here, we contribute to this challenge
using a box model of the isotopic carbon cycle [Köhler et
al., 2005] based on process understanding previously derived for
Termination I. Our results show that major features of the Vostok period are
reproduced while prior to Vostok our model predicts significantly smaller
amplitudes in CO2 variations.
Link to abstract
Updated! Link to slides
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Posted by admin on Thursday, September 29 @ 08:30:00 MDT (1045 reads)
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| Greenhouse Gas (CO2, CH4) and Climate Evolution since 650 kyrs Deduced from Anta | |
By Jean Marc Barnola
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.
Link to Abstract
Link to Slides
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Posted by admin on Thursday, September 29 @ 08:00:00 MDT (1064 reads)
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