8 Important New Research Papers!
ASW
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Subject: End of hospitable climate: Recent research
From: “Lance Olsen” <lance@wildrockies.org>
Date: Thu, July 24, 2008 12:16 pm
To: “cmcr-outreach” <cmcr-outreach@vortex.wildrockies.org>
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Public release date: 23-Jul-2008
Geophysical Research Letters (American Geophysical Union)
Contact: Peter Weiss
pweiss@agu.org
202-777-7507
AGU journal highlights — July 23, 2008
1. Fire suppression may have reduced carbon storage in western U.S. forests
Active fire suppression since the early twentieth
century has caused a widespread increase in
fire-intolerant trees, smaller trees, and the
density of stems growing on trees within western
U.S. forests. These factors have created thicker
forests and are thought to account for much of
North America’s carbon sink. To better quantify
changes in aboveground biomass, Fellows and
Goulden compare California forest inventories
from the 1930s with those from the 1990s. To
compare these data, interpolation measures are
used that result in underestimations of stem
density and biomass estimates for data from the
1930s. Nonetheless, the authors find that stem
density in these conifer forests increased by 34
percent between 1930 and 1990, reflecting an
increase in the number of small trees. However,
aboveground carbon stocks decreased by 26 percent
because large trees, which contain a
disproportionate amount of carbon, experienced a
net loss between the surveys. The authors
conclude that twentieth-century fire suppression
and the resulting increase in stand density may
have decreased, rather than increased, the amount
of biomass stored in western U.S. forests.
Title: Has fire suppression increased the amount
of carbon stored in western U.S. forests?
Authors: Aaron W. Fellows and Michael L. Goulden:
Department of Earth System Science, University of
California, Irvine, California, U.S.A..
Source: Geophysical Research Letters (GRL) paper
10.1029/2008GL033965, 2008;
http://dx.doi.org/10.1029/2008GL033965
2. New tracking method reveals giant volcanic clouds’ paths
On 17 August 1980, Iceland’s Hekla volcano
erupted, spewing a sulfur dioxide cloud into the
north polar stratosphere that reached roughly 15
kilometers (9 miles) in altitude. Although
satellites recorded this event, techniques that
exploit the strong absorption of infrared
radiation by sulfur dioxide have only recently
emerged, allowing scientists to reanalyze old
data to track volcanic gas clouds. Using the
ultraviolet data collected by the Nimbus 7 Total
Ozone Mapping Spectrometer and infrared data
collected by the High Resolution Infrared
Radiation Sounder (on NOAA’s Television Infrared
Observation Satellite (TIROS) Operational
Vertical Sounder), Carn et al. tracked sulfur
dioxide released by Hekla. They find that the
eruption emitted about 0.5 to 0.7 teragrams
(trillions of grams) of sulfur dioxide, which
later split into three distinct clouds, one of
which circled the North Pole for 6 days. The
others drifted across eastern Russia, Alaska, and
Canada. Through this analysis, the authors show
that integrated satellite sulfur dioxide
measurements may be used to test air parcel
trajectory models used for aviation hazard
mitigation. This study also highlights the
potential impacts of Icelandic volcanic eruptions
on the polar atmosphere and Arctic ozone loss.
Title: Circumpolar transport of a volcanic cloud from Hekla (Iceland)
Authors: S. A. Carn: Joint Center for Earth
Systems Technology (NASA/University of Maryland
Baltimore County), University of Maryland
Baltimore County, Baltimore, Maryland, U.S.A;
A. J. Prata: Atmosphere and Climate Department,
Norwegian Institute for Air Research (NILU),
Kjeller, Norway;
S. Karlsdóttir: Icelandic Meteorological Office, Reykjavík, Iceland.
Source: Journal of Geophysical
Research-Atmospheres (JGR-D) paper
10.1029/2008JD009878, 2008;
http://www.agu.org/journals/pip/jd/2008JD009878-pip.pdf
This paper is “in press”.
3. Frost risks to plants up, and down, in changing climate
As climate warms, scientists expect that the
bud-break and blooming cycles of plants will
start progressively earlier each year. Most
studies of the risk associated with early
blooming use simple increases in monthly mean
temperatures to represent future climate
scenarios. However, both the average and the
variation of daily temperatures are forecast to
increase in future climate scenarios; such
variation in temperatures increases the risk that
early bud-breaks are followed by damaging frost.
To study such frost risk to vegetation, Rigby and
Porporato developed a probabilistic model that
represents bud-break in the context of
fluctuating but warming temperatures. After
calibrating this model to temperature data from
Durham, N. C., the authors find that model
results show that frost risk is equally sensitive
to increases in daily temperature fluctuations
(which serves to increase frost risk) as to
increases in average temperatures (which serves
to decrease frost risk).
Title: Spring frost risk in a changing climate
Authors: J. R. Rigby and Amilcare Porporato:
Department of Civil and Environmental
Engineering, Duke University, Durham, North
Carolina, U.S.A.
Source: Geophysical Research Letters (GRL) paper
10.1029/2008GL033955, 2008;
http://dx.doi.org/10.1029/2008GL033955
4. Martian mineral layers offer tempting clues
Clay minerals such as montmorillonite and other
smectites have been previously detected in
layered outcrops in and around the Martian
outflow channel Mawrth Vallis. Wray et al.
additionally identify kaolinite and oxide
minerals such as hematite in the Mawrth Vallis
outcrops and find that these diverse minerals
occur in distinct stratigraphic horizons,
implying either that they formed over time under
different environmental conditions or that they
have distinctly different sediment sources. The
authors observe that this pattern of layers
occurs on both sides of the outflow channel and
on its floor, with aluminum-rich clay-bearing
layers typically overlying iron-rich clay
deposits. This, combined with high-resolution
topographic data, suggests that the aluminum-rich
clay-bearing layers are younger than the outflow
channel and may represent a later sedimentary or
altered volcanic ash deposit that drapes the
topography. Because of Mawrth Vallis’s distinct
layering history, the authors expect that this
would make a good location for future surface
missions to Mars to study geologic history and
ancient habitable environments on Mars.
Title: Compositional stratigraphy of clay-bearing
layered deposits at Mawrth Vallis, Mars
Authors: J. J. Wray and S. W Squyres: Department
of Astronomy, Cornell University, Ithaca, New
York, U.S.A.;
B. L. Ehlmann and J. F. Mustard: Department of
Geological Sciences, Brown University,
Providence, Rhode Island, U.S.A.;
R. L. Kirk: Astrogeology Program, U.S. Geological
Survey, Flagstaff, Arizona, U.S.A.
Source: Geophysical Research Letters (GRL) paper
10.1029/2008GL034385, 2008;
http://dx.doi.org/10.1029/2008GL034385
5. Uruguay River flow responds to climate, land-use changes
The Uruguay River basin has experienced extensive
land change during the second half of the
twentieth century as agricultural area expanded.
Concurrent with this has been an increase of
streamflow and precipitation due to atmospheric
dynamics. To help determine which factor-land use
change or atmospheric dynamics-has contributed
more to fluctuations in Uruguay River discharge,
Saurral et al. study streamflow along the Uruguay
River using a hydrology model run between 1960
and 2000 that explicitly accounts for the role of
land cover. The authors find that increases in
average streamflow are more likely attributable
to climatic variations, implying that land use
changes were not large enough to produce
appreciable changes in basin runoff. This is
perhaps because most land changes did not result
from deforestation but instead involved
converting grassland (pasture) to crops. However,
the authors note that basin response, namely,
that flows at the basin outlet now occur about 2
days sooner than in the 1960s, appears to be
attributable solely to land cover change between
the 1960s and the 1990s.
Title: Land use impact on the Uruguay River discharge
Authors: Ramiro I. Saurral and Vicente R. Barros:
Center for Atmospheric and Oceanic Research,
National Scientific and Technical Research
Council, University of Buenos Aires, Buenos
Aires, Argentina; also at Department of
Atmospheric and Ocean Sciences, University of
Buenos Aires, Buenos Aires, Argentina;
Dennis P. Lettenmaier: Department of Civil and
Environmental Engineering, University of
Washington, Seattle, Washington, U.S.A.
Source: Geophysical Research Letters (GRL) paper
10.1029/2008GL033707, 2008;
http://dx.doi.org/10.1029/2008GL033707
6. Reexamining stratosphere effects on lower-atmosphere warming
It is well established that the troposphere, the
atmospheric layer closest to the Earth’s surface,
significantly influences the circulation of the
stratosphere, the layer above the troposphere.
The alternate possibility, that the stratosphere
can have significant downward influence on
tropospheric circulation, is less well
established. Sigmond et al. investigate the
potential for such downward influence to alter
current predictions of global warming. Comparing
the predicted warming response in two general
circulation models-one with a well-resolved
stratosphere (high-top version) and one without a
well-resolved stratosphere (low-top version)-they
find significant differences. While similar
results in the past have been taken as evidence
that a well-resolved stratosphere is essential
for modeling future climate projections, the
authors question this conclusion. Instead, they
show that further analysis demonstrates that the
differing warming responses in the two models are
not related to the differing model lid height,
but are due to differing treatments of
parameterized gravity waves, which have a large
influence on the climatological winds in the
lower stratosphere.
Title: Impact of the stratosphere on tropospheric climate change
Authors: Michael Sigmond and Paul J. Kushner:
Department of Physics, University of Toronto,
Toronto, Ontario, Canada;
John F. Scinocca: Canadian Centre for Climate
Modelling and Analysis, Meteorological Service of
Canada, Victoria, British Columbia, Canada;
Source: Geophysical Research Letters (GRL) paper
10.1029/2008GL033573, 2008;
http://dx.doi.org/10.1029/2008GL033573
7. How are human-made aerosols changing clouds?
Human-generated aerosol particles affect solar
radiation by direct scattering and absorption,
but also change cloud properties through
particles acting as cloud condensation nuclei
(CCN) and ice nuclei (IN), a pathway referred to
as the “indirect aerosol effect.” This effect is
likely the manifestation of two different
aerosol-cloud interaction mechanisms. One
encompasses aerosols’ effect on cloud water,
specifically how a decrease in cloud particle
size decreases precipitation efficiency, thereby
increasing cloud lifetimes. Oreopoulos and
Platnick study the other mechanism, called the
Twomey effect, which involves the radiative
effect of cloud microphysical changes only (no
change in cloud water amount). Here the greater
availability of CCN or IN yields clouds with more
numerous but smaller cloud particles, and
therefore larger optical thickness. The authors
seek to quantify the spatial and temporal
sensitivity of liquid clouds to the Twomey effect
by studying data from NASA’s satellite-based
Moderate Resolution Imaging Spectroradiometer for
4 months in 2005. Through the global maps
generated, they find that the detailed nature of
cloud microphysical perturbations, as well as the
unperturbed cloud properties, is important for
determining the radiative forcing associated with
the Twomey effect.
Title: The radiative susceptibility of cloudy
atmospheres to droplet number perturbations, part
2: Global analysis from MODIS
Authors: Lazaros Oreopoulos and Steven Platnick:
Joint Center for Earth Systems Technology,
University of Maryland Baltimore County,
Baltimore, Maryland, U.S.A.; and Laboratory for
Atmospheres, NASA Goddard Space Flight Center,
Greenbelt, Maryland, U.S.A.
Source: Journal of Geophysical
Research-Atmospheres (JGR-D) paper
10.1029/2007JD009655, 2008;
http://www.agu.org/journals/pip/jd/2007JD009655-pip.pdf
This paper is “in press”.
8. Taking sharper look at key atmospheric region
The middle atmosphere is composed of the
stratosphere and mesosphere and extends from
about 12 to 90 kilometers (7.5 to 56 miles) in
altitude. This region is important because it
houses ozone, which shields the Earth from
ultraviolet light, and gravity and planetary
waves, which influence weather close to the
Earth’s surface. Many atmospheric general
circulation models (GCMs) currently used for
climate studies do not have sufficiently high
spatial resolution to resolve small-scale gravity
waves. To understand the roles of such
small-scale phenomena in the Earth’s climate,
Watanabe et al. develop a new GCM that uses very
high spatial resolution. This model has
horizontal resolution of 0.5625 degrees in
latitude and longitude, and covers a region that
extends from the surface to a height of about 85
km (53 mi) with uniform vertical resolution of
300 meters (980 feet) throughout the middle
atmosphere. This GCM successfully simulates the
spontaneous generation of gravity waves by
convection, topography, instability, and
adjustment processes, as well as their
propagation and dissipation, resulting in a
realistic reproduction of general circulation in
the midlatitude and polar stratosphere and
mesosphere.
Title: General aspects of a T213L256 middle
atmosphere general circulation model
Authors: Shingo Watanabe, Yoshio Kawatani, and
Kazuyiki Miyazaki: Frontier Research Center for
Global Change, Japan Agency for Marine-Earth
Science and Technology, Yokohama, Japan;
Yoshihiro Tomikawa: National Institute of Polar Research, Tokyo, Japan;
Masaaki Takahashi: Frontier Research Center for
Global Change, Japan Agency for Marine-Earth
Science and Technology, Yokohama, Japan; Also at
Center for Climate System Research, University of
Tokyo, Kashiwa, Japan;
Kaoru Sato: Department of Earth and Planetary
Science, Graduate School of Science, University
of Tokyo, Tokyo, Japan.
Source: Journal of Geophysical
Research-Atmospheres (JGR-D) paper
10.1029/2008JD010026, 2008;
http://dx.doi.org/10.1029/2008JD010026
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