The following highlights summarize research papers that have
been published or accepted for publication (paper in press) in
Geophysical Research Letters (GRL).
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1. Second volcano helped chill coldest decade on
record
The extremely cold temperatures during the latter part of the
decade from 1810 to 1819 - the coldest decade on record during the
past 500 years - have been attributed mainly to the enormous 1815
eruption of the Tambora volcano in Indonesia. Such large volcanic
eruptions cool the planet by spewing ash and gases into the
stratosphere, where they form sulfate aerosols that block sunlight.
But what accounts for the abnormally chilly temperatures earlier in
the decade, between 1810 and 1815? Some recent studies have
suggested that an unrecorded large volcanic eruption occurred
around 1809. To investigate further, Cole-Dai et al. analyze ice
cores from Greenland and Antarctica. In the 1809–to-1810 snow
layers, the authors find anomalous sulfur isotopes that must have
resulted from chemical reactions that could only have occurred in
the stratosphere following a very large volcanic eruption. The
results, which help improve understanding of volcanoes' effects on
climate, provide the first compelling evidence that an unknown
large volcanic eruption occurred in the tropics in early 1809 and
contributed to the coldest decade in recorded history.
Title: Cold Decade (AD 1810 to 1819) Caused by Tambora (1815)
and Another (1809) Stratospheric Volcanic Eruption
Authors: Jihong Cole-Dai, David Ferris, and Alyson Lanciki:
Department of Chemistry and Biochemistry, South Dakota State
University, Brookings, South Dakota, USA;
Joël Savarino: Laboratoire de Glaciologie et
Géophysique de l´Environnement, CNRS/Université
Joseph Fourier – Grenoble 1, 38400 Saint Martin
d´Hères, France;
Mélanie Baroni: CEREGE, Collège de France,
Université Paul Cézanne, UMR6635, CNRS,
Aix-en-Provence, France;
Mark H. Thiemens: Department of Chemistry and Biochemistry,
University of Califronia, San Diego, La Jolla, California, USA.
Source: Geophysical Research Letters (GRL) paper in
press; http://www.agu.org/journals/pip/gl/2009GL040882-pip.pdf
2. Stalagmite climate record disputes ice-core
findings
During the last glacial period, a number of rapid climate
variations known as Greenland interstadials (GIs; also known as
Dansgaard-Oeschger events) took place. These climate shifts have
been observed in ice core records, but the precise timing of these
events has been uncertain. To assign precise ages to some of the GI
events, Fleitmann et al. obtain a new, well-dated carbon and oxygen
isotope record from stalagmites in the Sofular Cave in northwestern
Turkey. The authors note that the new stalagmite record, which
covers the past 50,000 years, differs from the most recent
Greenland ice core chronology by as much as several centuries at
some points. Furthermore, although some scientists had suggested
that GIs occurred on a 1470-year cycle, the new stalagmite record
does not support that interpretation, the authors find. They also
note that the new record indicates that the climate and ecosystem
in the eastern Mediterranean changed rapidly in response to the
GIs; these changes could have affected Neanderthal populations
living in the area.
Title: Timing and climatic impact of Greenland interstadials
recorded in stalagmites from northern Turkey
Authors: D. Fleitmann, S. Badertscher, and O. M.
Göktürk: Institute of Geological Sciences, University of
Bern, Bern, Switzerland and Oeschger Centre for Climate Change
Research, University of Bern, Bern, Switzerland;
H. Cheng: Department of Geology and Geophysics, University of
Minnesota-Twin Cities, Minneapolis, Minnesota, USA;
R. L. Edwards: Department of Geology and Geophysics, University
of Minnesota-Twin Cities, Minneapolis, Minnesota, USA;
M. Mudelsee: Climate Risk Analysis, Hannover, Germany;
A. Fankhauser, R. Pickering, A. Matter, and J. Kramers:
Institute of Geological Sciences, University of Bern, Bern,
Switzerland;
C. C. Raible: Oeschger Centre for Climate Change Research,
University of Bern, Bern, Switzerland, and Climate and
Environmental Physics, Physics Institute, University of Bern, Bern,
Switzerland;
O. Tüysüz: Eurasia Institute of Earth Sciences,
Istanbul Technical University, Istanbul, Turkey.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL040050, 2009; http://dx.doi.org/10.1029/2009GL040050
3. Model explains Colorado plateau uplift
The mechanisms driving the evolution of the Colorado plateau in
the past 30 million years have been the focus of debate among
geologists. To address the issue, Moucha et al. create a numeric
model that reconstructs mantle flow during the past 30 million
years and track the induced topographic changes due to a mantle
upwelling. The study confirms that the tectonic evolution of the
southwestern United States has been influenced by mantle upwelling
associated with the ancient northern portion of the East Pacific
Rise. The authors note that uplift of the southern Colorado plateau
totaled about 1 kilometer (0.6 mile) in the past 20 million years.
In the past 10 million years, the center of uplift moved
northeastward from the southwestern rim of the plateau.
Furthermore, they suggest that the uplift of 100 to 300 meters (330
to 980 feet) in the past 5 million years may have played an
important role in the formation of the Grand Canyon by establishing
a gradient in the flow direction of the Colorado River.
Title: Deep mantle forces and the uplift of the Colorado
Plateau
Authors: Robert Moucha and Alessandro M. Forte: GEOTOP,
Université du Québec à Montréal,
Montreal, Quebec, Canada;
David B. Rowley: Department of the Geophysical Sciences,
University of Chicago, Chicago, Illinois, USA;
Jerry X. Mitrovica: Department of Earth and Planetary Sciences,
Harvard University, Cambridge, Massachusetts, USA;
Nathan A. Simmons: Atmospheric, Earth, and Energy Division,
Lawrence Livermore National Laboratory, Livermore, California,
USA;
Stephen P. Grand: Jackson School of Geological Sciences,
University of Texas at Austin, Austin, Texas, USA.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL039778, 2009 http://dx.doi.org/10.1029/2009GL039778
4. Australian lake deposits weigh against Mars climate
shift
In recent years the discovery of two different types of mineral
deposits - sulfates and phyllosilicates - in close proximity on
Mars led scientists to suggest that a significant global climate
change must have occurred. However, others have suggested that
these minerals could actually have formed under the same climatic
conditions. To help resolve the issue, Baldridge et al. examine
chemical and mineral data from acidic saline lakes in Western
Australia, which have been recognized as a useful chemical analog
for mineral formation on Mars. They note that Western Australian
lakes have large pH differences separated by only a few tens of
meters (tens to more than hundred feet), which shows that variable
chemistries can coexist. On the basis of Australian lake data, the
authors suggest an alternative Martian mineral formation mechanism
in which some phyllosilicates could have formed in the neutral or
alkaline subsurface while sulfates formed near the surface in more
acidic conditions. The authors conclude that Mars had a complex
hydrological history and the phyllosilicates and sulfates may be
separated by chemical gradients rather than by temporal
boundaries.
Title: Contemporaneous deposition of phyllosilicates and
sulfates: Using Australian acidic saline lake deposits to describe
geochemical variability on Mars
Authors: A. M. Baldridge, S. J. Hook, and N. T. Bridges: Jet
Propulsion Laboratory, California Institute of Technology,
Pasadena, California, USA;
J. K. Crowley: U.S. Geological Survey, Reston, Virginia,
USA;
G. M. Marion: Desert Research Institute, Reno, Nevada, USA;
J. S. Kargel: Department of Hydrology and Water Resources,
University of Arizona, Tucson, Arizona, USA;
J. L. Michalski: Institut d'Astrophysique Spatiale,
Université Paris Sud, Orsay, France;
B. J. Thomson: Johns Hopkins University Applied Physics
Laboratory, Laurel, Maryland, USA;
C. R. de Souza Filho: Department of Geology and Natural
Resources, University of Campinas, Campinas, Brazil;
A. J. Brown: SETI Institute, Mountain View, California, USA.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL040069, 2009; http://dx.doi.org/10.1029/2009GL040069
5. How bushfires and Indian Ocean conditions are
linked
Southeastern Australia has been hit by several serious bushfires
in recent years, including the devastating February 2009 "Black
Saturday" fire, which killed more than 170 people. To improve
understanding of how climate change may affect the occurrence of
bushfires, Cai et al. examine the connection between bushfires and
positive Indian Ocean Dipole (pIOD) events. Such events are a phase
in which the eastern Indian Ocean is cooler than usual while the
western Indian Ocean is warmer than usual. These conditions tend to
lead to lower than average rainfall and higher temperatures over
southeastern Australia. The authors find that pIODs reduce the soil
moisture, increasing the fuel load leading into summer.
Furthermore, they show that of 16 pIOD events since 1950, 11 were
followed by major bushfires, and of the past 21 major bushfires, 11
were preceded by pIOD. The authors also found that bushfires are
more strongly associated with pIOD events than with El Niño
events. Because global warming is likely to increase the frequency
of pIOD events, the authors suggest that bushfire risk will also
increase.
Title: Positive Indian Ocean Dipole events precondition
southeast Australia bushfires
Authors: W. Cai and T. Cowan: Wealth from Oceans Flagship, CSIRO
Marine and Atmospheric Research, Aspendale, Victoria,
Australia;
M. Raupach: CSIRO Marine and Atmospheric Research, Canberra,
ACT, Australia.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL039902, 2009; http://dx.doi.org/10.1029/2009GL039902
6. Benefits, risks, and costs of geoengineering
Stratospheric geoengineering, in which the precursors of sulfate
aerosols are injected into the atmosphere, has been suggested as a
possible way to reduce global warming. Aerosols would block
sunlight from reaching the surface, thereby cooling the planet.
Although such projects are impossible using current technology,
geoengineering schemes are being considered as an option in case
efforts to mitigate global warming fail. Robock et al. evaluate the
benefits, risks, and costs of stratospheric geoengineering and find
that the cost of using existing U.S. military planes to inject
aerosol precursors into the atmosphere would be several billion
dollars per year; other methods, including artillery and weather
balloons, would cost more. The authors point out some of the
benefits of geoengineering: It would cool the planet, reduce the
melting of sea ice, reduce sea level rise, and increase plant
productivity. However, they note that there are also many risks,
including potential drought in some regions, continued ocean
acidification, less sunlight for solar power, possible unexpected
consequences, rapid warming if geoengineering were stopped,
potential moral hazards, and problems for terrestrial
astronomy.
Title: Benefits, risks, and costs of stratospheric
geoengineering
Authors: Alan Robock, Allison Marquardt, Ben Kravitz, and
Georgiy Stenchikov: Department of Environmental Sciences, Rutgers
University, New Brunswick, New Jersey, USA.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL039209, 2009; http://dx.doi.org/10.1029/2009GL039209
7. Detecting water vapor trend would take 50 years
Water vapor in the upper troposphere contributes to the
greenhouse effect, and scientists predict that humidity will
increase in the future along with rising levels of atmospheric
carbon dioxide. However, there is currently no observing program
that could detect the predicted trends. To determine instrumental
needs to measure long-term changes in upper tropospheric water
vapor, Boers and van Meijgaard analyze how frequently and for how
long observations would need to be made to clearly detect a trend
in upper tropospheric water vapor. They used a regional climate
model to simulate a perfect 150-year humidity record, and then
sample from the model data to simulate realistic radiosonde water
vapor observations with various observation frequencies. The
analysis shows that it would take 30 years for a clear trend to
show up in the perfect record; sampling every four days, it would
take at least 50 years of observations to detect this trend. The
authors suggest that these results, along with economic
considerations, should be an important consideration for those
planning an atmospheric water vapor monitoring program.
Title: What are the demands on an observational program to
detect trends in upper tropospheric water vapor anticipated in the
21st century?
Authors: R. Boers and E. van Meijgaard: Royal Netherlands
Meteorological Institute, De Bilt, Netherlands
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL040044, 2009; http://dx.doi.org/10.1029/2009GL040044
8. Understanding distributions of energetic electrons
During geomagnetic storms, high-energy electrons from the
Earth's outer magnetosphere can enter the atmosphere, where they
can affect atmospheric chemistry and may alter climate by
destroying ozone. To improve knowledge of the special and temporal
distribution of this energetic electron precipitation, Horne et al.
analyze 9 years of data from low-altitude satellites for different
phases of geomagnetic storms. They find that precipitation of
electrons with energy greater than 300 keV (thousand electron
volts) peaks during the main phase of geomagnetic storms, whereas
precipitation of electrons with energy greater than 1 MeV (million
electron volts) peaks later, after the geomagnetic storm peak.
Furthermore, 300-keV electron precipitation occurs at all
longitudes in both hemispheres, whereas 1-MeV electron
precipitation occurs mainly in the Southern Hemisphere southward of
the South Atlantic anomaly, a known weakness in Earth's magnetic
field. This indicates that different processes are responsible for
scattering different energy electrons into the atmosphere. The
authors suggest that these results should be considered in models
of the atmospheric response to geomagnetic storms and solar
variability.
Title: Energetic electron precipitation from the outer radiation
belt during geomagnetic storms
Authors: Richard B. Horne and Mai Mai Lam: British Antarctic
Survey, Cambridge, UK;
Janet C. Green: Space Weather Prediction Center, National
Oceanic and Atmospheric Administration, Boulder, Colorado, USA.
Source: Geophysical Research Letters (GRL) paper
10.1029/2009GL040236, 2009; http://dx.doi.org/10.1029/2009GL040236
SOURCE