AGU journal highlights -- Nov. 5, 2009

The following highlights summarize research papers that have been published in Geophysical Research Letters (GRL).

In this release:

1. Antarctica warming a regional, not local, trend
   
2. New model factors storms into shoreline loss
   
3. Study agrees reservoir contributed to Wenchuan earthquake
   
4. Much Arctic warming linked to sea-ice, cloud-cover changes
   
5. Sorting out natural from human influences in ocean warming
   
6. Meteoritic impacts may have cooked up life's components

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In the past 50 years, considerable warming has been observed in the northern Antarctic Peninsula. Understanding whether these measured changes are a local phenomenon or part of a significant regional trend is important for interpreting observations, validating climate models, and predicting future climate change. To investigate the extent of the warming, Thomas et al. present a new 150-year oxygen isotope record from an ice core drilled in the data-sparse southwestern Antarctic Peninsula. The new record shows about 2.7 degrees Celsius (4.9 degrees Fahrenheit) increase in surface temperature since the 1950s. The record correlates well with satellite-derived temperature reconstructions and records from other locations showing similar warming trends. The authors conclude that the warming in the past 50 years has been a regional trend, not a local phenomenon, and has been part of a statistically significant 100-year warming trend that began around 1900. Furthermore, they use climate models to show that the observed warming trend is outside the expected range of natural variability and is therefore probably the result of human influence.

Title:
Ice core evidence for significant 100-year regional warming on the Antarctic Peninsula

Authors:
E. R. Thomas, T. J. Bracegirdle, and C. Franzke: British Antarctic Survey, Cambridge, UK;

P. F. Dennis: School of Environmental Sciences, University of East Anglia, Norwich, UK.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL040104, 2009

http://dx.doi.org/10.1029/2009GL040104

2. New model factors storms into shoreline loss

Rising sea levels are predicted to result in shoreline loss and the displacement of many people living near shores. In this context, scientists need to have an accurate understanding of historical rates of shoreline change. Large storms affect shores, but shorelines often recover quickly and return to long-term trends. Some models remove storm-influenced shorelines from data when estimating a long-term trend, but it can be difficult to tell whether a shoreline is influenced by a storm; many models of shoreline change treat storms as noise, which causes inaccuracies. To improve estimates of shoreline change, Frazer et al. develop a storm function to explicitly include storms in shoreline change models. They apply their method to data from Cotton Patch Hill, Delaware, and find a long-term rate of shoreline loss of approximately 0.49 meters (1.6 feet) per year, about 16 percent lower than previous estimates.

Title:
Modeling storms improves estimates of long-term shoreline change

Authors:
L. Neil Frazer, Tiffany R. Anderson, and Charles H. Fletcher: Department of Geology and Geophysics, School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, Hawaii, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL040061, 2009

http://dx.doi.org/10.1029/2009GL040061

3. Study agrees reservoir contributed to Wenchuan earthquake

Reservoirs have been known to trigger earthquakes because the change in water level can add to stress on nearby faults. Some scientists have suggested that the Zipingpu Reservoir, completed in 2005, may have triggered the devastating 2008 Wenchuan earthquake in China that killed nearly 90,000 people. However, this suggestion has been controversial. To evaluate the possible effect of the Zipingpu Reservoir on the Wenchuan earthquake, Ge et al. construct a two-dimensional model to study how the reservoir changed the stresses on the nearby faults. The authors consider changes in static stress due to weight of the water and changes in pore pressure in the rocks beneath the reservoir due to fluid diffusion. They estimate that the Zipingpu reservoir increased stress on the nearby faults by enough to have speeded up their rupture by tens to hundreds of years. The authors point out that resolving the question of whether the Zipingpu Reservoir contributed to the Wenchuan earthquake is important for understanding reservoir and earthquake hazards, especially in regions where dams are being rapidly built near faults.

Title:
Did the Zipingpu Reservoir Trigger the 2008 Wenchuan Earthquake?

Authors:
Shemin Ge: Department of Geological Sciences, University of Colorado, Boulder, Colorado, USA;

Mian Liu and Gang Luo: Department of Geological Sciences, University of Missouri, Columbia, Missouri, USA;

Ning Lu: Division of Engineering, Colorado School of Mines, Golden, Colorado, USA
Jonathan W. Godt: U.S. Geological Survey, Denver, Colorado, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL040349, 2009

http://dx.doi.org/10.1029/2009GL040349

4. Much Arctic warming linked to sea-ice, cloud-cover changes

The Arctic has been changing dramatically in the past 20 years, and many factors contribute to the observed surface temperature trends. Liu et al. analyze the influence of trends in sea ice concentration and cloud cover on surface temperature in the Arctic from 1982 to 2004. They find that sea ice concentration and cloud cover play a large role in observed temperature trends. For instance, their analysis shows that surface warming associated with sea ice accounts for more than 0.9 degrees Celsius (1.62 degrees Fahrenheit) per decade of the observed 1.1 degrees Celsius (about 2 degrees Fahrenheit) per decade warming trend in autumn. In addition, in winter, cloud cover changes explain 0.91 degrees Celsius (1.64 degrees Fahrenheit) of the 1.2 degrees Celsius (2.16 degrees Fahrenheit) per decade surface temperature cooling, and in spring, 0.55 degrees Celsius (0.99 degrees Fahrenheit) per decade of the total 1 degree Celsius (1.8 degree Fahrenheit) per decade warming is attributable to cloud cover. The authors note that their model provides insight into the causes of recent temperature trends and could be extended to study the influences of other parameters such as sea ice thickness.

Title:
The Influence of Changes in Sea Ice Concentration and Cloud Cover on Recent Arctic Surface Temperature Trends

Authors:
Yinghui Liu and Xuanji Wang: Cooperative Institute for Meteorological Satellite Studies,
University of Wisconsin-Madison, Madison, Wisconsin, USA;

Jeffrey R. Key: Center for Satellite Applications and Research, NESDIS, NOAA, Madison, Wisconsin, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL040708, 2009

http://dx.doi.org/10.1029/2009GL040708

5. Sorting out natural from human influences in ocean warming

As increased greenhouse gas concentrations cause global temperatures to rise, much of the heat that builds up in the climate system is taken up in the oceans through air-sea heat interchange. However, ocean temperatures are also strongly influenced by natural variability associated with circulation changes, especially in the North Atlantic, which is overrepresented in the observational record. This can result in inaccurate estimates of the roles of natural and anthropogenic factors in ocean temperature changes. To improve understanding of human influence on ocean warming, Palmer et al. present a new method of analysis that filters out the ocean temperature changes due to internal variability. The method can be applied to both model simulations and observations. This gives a clearer picture of the amount of ocean warming caused by externally driven air-sea heat interchanges and results in significantly better agreement between models and observations. The authors believe their method will help improve studies of natural ocean temperature variation and changes caused by human activity.

Title:
A new perspective on warming of the global oceans

Authors:
M. D. Palmer, S. A. Good, N. A. Rayner, and P. A. Stott: Met Office Hadley Centre, Exeter, UK;

K. Haines: Environmental Systems Science Centre, University of Reading, Reading, UK.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL039491, 2009

http://dx.doi.org/10.1029/2009GL039491

6. Meteoritic impacts may have cooked up life's components

It has been suggested that the organic matter needed for the origin of life could have been delivered to Earth through meteoritic impacts early in Earth's history, but studies have shown that most of the delivered organics would have decomposed through shock heating or aerodynamic interaction with the ambient atmosphere. However, Sugita and Schultz suggest that some of the decomposed organics could have been revived through chemical reactions between the meteoritic matter and the ambient atmosphere during hypervelocity oblique impacts. As a model for meteoritic impacts in the early atmosphere, they conduct hypervelocity impact experiments in which polycarbonate projectiles impact copper targets in very oxidizing nitrogen-oxygen-argon mixtures, which provide difficult conditions for organic synthesis. Despite the conservative conditions, they find that carbon from the projectile reacts efficiently with atmospheric nitrogen to produce cyanides. Nitrogen is an important element in biomolecules but is not abundant in meteorites. The authors note that impact-driven cyanide synthesis may have contributed significantly to the basic chemical building blocks needed for the origin of life.

Title:
Efficient cyanide formation due to impacts of carbonaceous bodies on a planet with a nitrogen-rich atmosphere

Authors:
Seiji Sugita: Department of Complexity Science and Engineering, University of Tokyo , Kashiwa, Japan;

Peter H. Schultz: Department of Geological Sciences, Brown University, Providence, Rhode Island, USA.

Source:
Geophysical Research Letters (GRL) paper 10.1029/2009GL040252, 2009

http://dx.doi.org/10.1029/2009GL040252

Source: American Geophysical Union