Public Release:  AGU journal highlights -- July 30, 2013

American Geophysical Union

The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL) and Journal of Geophysical Research-Solid Earth (JGR-B).

In this release:

1. Atmospheric rivers linked to severe precipitation in Western Europe
2. Warming climate increases rainfall extremes
3. Carbon fertilization increased arid region leaf cover over past 20 years
4. Understanding the complexities of volcanoes that erupt just once
5. Revealing the early seafloor spreading history between India and Australia
6. Independent observations corroborate surface air temperature record

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1. Atmospheric rivers linked to severe precipitation in Western Europe

Atmospheric rivers, narrow bands of enhanced water vapor transport in the atmosphere, have been associated with extreme rainfall and flooding in some areas, especially western North America. Lavers and Villarini now show that atmospheric rivers are also responsible for a significant number of days of high precipitation in Western Europe.

The authors investigated the link between atmospheric rivers and annual maxima daily precipitation across Europe over the period from 1979 to 2011. First they applied an algorithm to identify atmospheric rivers in water vapor transport data and detected a total of 432 atmospheric rivers over the study period. Then they looked at the dates of the annual maxima precipitation events and connected an atmospheric river with a maximum precipitation event if the precipitation occurred on the same day or the day after an atmospheric river occurred.

They find that the effects of atmospheric rivers are felt as far inland as Germany and Poland, with the strongest links between high precipitation events and atmospheric rivers in mountainous areas. In some regions, most of the largest annual maxima precipitation events were linked to atmospheric rivers. For instance, in some parts of Scotland, southwest England, northern France, and Norway, 8 of the 10 top annual maxima precipitation events were associated with atmospheric rivers. The results show that atmospheric rivers are important in explaining the extreme precipitation distribution in Western Europe.

Source: Geophysical Research Letters, doi: 10.1002/grl.50636, 2013

Title: The nexus between atmospheric rivers and extreme precipitation across Europe

Authors: David A. Lavers and Gabriele Villarini: IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, Iowa, USA.

2. Warming climate increases rainfall extremes

In recent years there have been a number of prolonged heat waves and heavy rain events, and studies are showing that global climate warming is increasing the risk of extreme rainfall and drought. To add to the evidence linking climate warming and extreme precipitation and provide a regional as well as global perspective, Lau et al. analyzed projections from 14 different climate models that are part of the CMIP5 project, which is organized by the Intergovernmental Panel on Climate Change in preparation for its upcoming fifth assessment report.

The authors examined not only total rain, but also changes in heavy, moderate, and light rain, as well as drought, on global and regional scales. They find that under a 1 percent per year increase in carbon dioxide emissions, which is comparable to a business-as-usual scenario, the ensemble of models predicts that by the time carbon dioxide emissions triple, globally extremely heavy rain would increase by 100 to 250 percent, moderate rain would decrease by 5 to 10 percent, and light rain would increase by 10 to 15 percent. There would also be a global increase in dry months of up to 16 percent, with the largest risk of drought in areas that are already dry, including northern Africa, southern Africa, and southern Europe, as well as the southwestern United States and Mexico and northeastern Brazil. The increased heavy precipitation would likely be concentrated in wet regions, including the equatorial Pacific Ocean and Asian monsoon areas.

The results add to growing evidence that increased carbon dioxide emissions will change global precipitation patterns. The increased risk of severe floods and droughts globally is associated with an adjustment in the large-scale circulation in response to the heat imbalance induced by global warming.

Source: Geophysical Research Letters, doi: 10.1002/grl.50420, 2013

Title: A canonical response of precipitation characteristics to global warming from CMIP5 models

Authors: William. K.-M. Lau: Earth Science Division, Atmospheres, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA;

H.-T. Wu: Science Systems and Applications, Inc., Lanham, Maryland, USA;

K.-M. Kim: Goddard Earth Science Technology & Research, Morgan State University, Baltimore, Maryland, USA.

3. Carbon fertilization increased arid region leaf cover over past 20 years

Satellite observations made from 1982 to 2010 have shown that warm, arid regions--such as the U.S. Southwest and Mexico, the deserts of Argentina, the Middle East, central and western Australia, and the regions that ring the Sahara--are getting greener. Researchers have long argued that increasing atmospheric carbon dioxide will fertilize enhanced plant growth. Carbon dioxide is a fuel source for plants' photosynthesis. In water-limited regions an increased atmospheric carbon dioxide concentration would allow plants to absorb the gas they need, while minimizing water loss. However, attributing the observed greening to the so-called carbon fertilization effect (and showing that it is not due to changes in water or nutrient availability or other factors) is difficult.

In warm, dry regions, plant growth is often controlled by water availability. In these areas the effects of carbon fertilization on foliage cover are expected to be most pronounced, and it is changes in cover that can be detected from satellites. By focusing on arid regions worldwide and controlling observations of plant foliage cover change for differences in precipitation rate, Donohue et al. find that carbon fertilization has caused an 11 percent increase in foliage cover from 1982 to 2010. This increased foliage cover was driven by a 14 percent increase in the atmospheric carbon dioxide concentration over the same period. As such, the carbon fertilization effect is already a prominent driver of land surface processes--at least in warm, arid environments. The authors note that though carbon fertilization may be occurring in some way in other ecosystems, the same strong relationship between increasing atmospheric carbon dioxide and foliage cover likely does not extend globally.

Source: Geophysical Research Letters, doi:10.1002/grl.50563, 2013

Title: Impact of CO2 fertilization on maximum foliage cover across the globe's warm, arid environments

Authors: Randall J. Donohue and Tim R. McVicar: CSIRO Land and Water, Canberra, Australia;

Michael L. Roderick: Research School of Biology, The Australian National University, Canberra, Australia, Research School of Earth Sciences, The Australian National University, Canberra, Australia and Australian Research Council Centre of Excellence for Climate System Science;

Graham D. Farquhar: Research School of Biology, The Australian National University, Canberra, Australia.

4. Understanding the complexities of volcanoes that erupt just once

Most of the world's volcanoes erupt only once, and, often, only for a short time--a few days to a couple weeks. Because of the brevity of the eruptions, and possibly because of a presumed docility, singly-erupting volcanoes, known as monogenetic volcanoes, are not nearly as well-studied as their polygenetic fellows. Traditionally researchers have assumed that monogenetic volcanic eruptions are simple in their dynamics. A new investigation by Barde-Cabusson et al., however, reveals that these volcanic eruptions can be highly complex, sometimes incorporating multiple phases and magma vents.

Using high-resolution electrical resistivity tomography, the authors retrospectively investigated the dynamics of the eruptions of three monogenetic volcanoes--Pujalós, Montsacopa, and Puig d'Adri--located in the Garrotxa volcanic field of northern Spain. The materials produced by different types of eruptions, such as mildly explosive Strombolian eruptions or hydromagmatic eruptions (when magma interacts with water), have different electrical resistivities. By studying how the electrical resistivity of the material layered on the outside of the volcanoes changed with depth, the researchers could reconstruct the volcanoes' eruptive styles.

The authors find that their application of electrical resistivity tomography enabled them to identify not only different eruptive styles but also shifts in eruptive dynamics. They also discovered a second, previously-unknown vent in one of the volcanoes. Further, the authors report what they suggest is the first observation of the eruptive conduit inside a monogenetic volcano.

Source: Geophysical Research Letters, doi:10.1002/grl.50538, 2013

Title: Electrical resistivity tomography revealing the internal structure of monogenetic volcanoes

Authors: Stéphanie Barde-Cabusson, Xavier Bolós, Dario Pedrazzi and Joan Martí: Institute of Earth Sciences Jaume Almera, ICTJA-CSIC, Lluis Sole i Sabaris, Barcelona, Spain;

Raul Lovera and Albert Casas: Economic and Environmental Geology and Hydrology Group, Department of Geochemistry, Petrology and Geological Prospecting, Faculty of Geology, University of Barcelona, Martí i Franqués, Barcelona, Spain;

Guillem Serra: Polytechnic University of Catalonia, C/Gran Capitán, Barcelona, Spain.

5. Revealing the early seafloor spreading history between India and Australia

The Perth Abyssal Plain, a section of ocean floor that lies off the western coast of Australia, formed as India and Australia broke away from what had been the supercontinent Gondwana, beginning around 130 million years ago. Oceanic crust within the Perth Abyssal Plain is the only region of preserved seafloor that directly records the early history of relative motion between India and Australia, but the lack of magnetic data collected in that region had made it difficult for scientists to validate tectonic models of the motion of those continents.

Now, Williams et al. present new magnetic data, collected across the Perth Abyssal Plain in October and November 2011 from the R/V Southern Surveyor, that place significant new constraints on the early seafloor spreading history of India and Australia.

The new magnetic anomaly data reveal previously unrecognized magnetic anomalies in the western Perth Abyssal Plain. The crust in the western part of the basin formed as part of the Indian Plate during the early stages of seafloor spreading between Australia and India. The crust that initially formed the Indian Plate was later transferred to the Australian Plate by a westward jump of the spreading ridge, which also led to fragments of the Indian continent being broken off and becoming stranded in the Indian Ocean. The study should be useful in tectonic models of the breakup of eastern Gondwana.

Source: Journal of Geophysical Research-Solid Earth, doi:10.1002/jgrb.50239

Title: Early India-Australia spreading history revealed by newly detected Mesozoic magnetic anomalies in the Perth Abyssal Plain

Authors: Simon E. Williams and Dietmar R. Müller: Earthbyte Group, School of Geosciences, University of Sydney, Sydney, New South Wales, Australia;

Joanne M. Whittaker; Earthbyte Group, School of Geosciences, University of Sydney, Sydney, New South Wales, Australia, and The Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia;

Roi Granot: Department of Geological and Environmental Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel.

6. Independent observations corroborate surface air temperature record

One of the most important foundations of scientists' understanding of global climate change is the land surface air temperature record, the long-term observations of air temperature measured 2 meters (6.5 feet) above the ground. These observations have been made around the world, for more than a century in some places. The air temperature records have shown a long-term warming trend due mainly to anthropogenic climate change, and variability seen in the air temperature record is used to guide models of the future climate.

Throughout the long observational record, the techniques used to measure air temperature have evolved. Observation stations have been moved, the land around the stations has changed, and the distribution of research stations has been heavier in urban and agricultural regions than in remote plots of land. Gridded temperature data sets have been designed to account for these biases and sources of uncertainty. However, for these and other reasons, some scientists and political figures have questioned the accuracy and validity of the historical air temperature record, arguing against its usefulness for understanding historical temperature trends and variability.

In response to these critics, Compo et al. calculated an independent record of historical land surface air temperatures that used a range of historical observations but did not use any measurements of air temperature itself. As such, any problems in the existing air temperature record that stem from changing techniques or tools or other factors would not appear in the authors' new record. The authors find that their independent temperature record largely aligned with existing air temperature records from 1901 to 2010, corroborating the validity of the widely used land surface air temperature record.

Source: Geophysical Research Letters, doi:10.1002/grl.50425, 2013

Title: Independent confirmation of global land warming without the use of station temperatures

Authors: Gilbert P. Compo, Prashant D. Sardeshmukh and Chesley McColl: Cooperative Institute for Research in Environmental Sciences, University of Colorado and Physical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA;

Jeffrey S. Whitaker: Physical Sciences Division, Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colorado, USA;

Philip Brohan: Met Office Hadley Centre, Exeter, UK;

Philip D. Jones: Climatic Research Unit, University of East Anglia, Norwich, UK, and Center of Excellence for Climate Change Research, Department of Meteorology, King Abdulaziz University, Jeddah, Saudi Arabia.



Mary Catherine Adams
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