AGU Journal Highlights
18 October 2011
Highlights, including authors and their institutions
The following highlights summarize research papers that have been recently published in Geophysical Research Letters (GRL), Journal of Geophysical Research-Atmospheres (JGR-D), and Journal of Geophysical Research-Oceans (JGR-C).
- Arctic ice is thinning and drifting faster than estimated by models
- Changing climate increases algae and plankton in the Arctic
- Tracking contributors to sea-level rise
- Lakes an important source of carbon emissions
- Climate model's historical accuracy no guarantee of future success
- Earthquake visualization shows ground motion in real time
Anyone may read the scientific abstract for any already-published paper by clicking on the link provided at the end of each Highlight. You can also read the abstract by going to Search Options and inserting into the search engine the full doi (digital object identifier), e.g. 10.1029/2011JC007110. The doi is found at the end of each Highlight below.
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1. Arctic ice is thinning and drifting faster than estimated by models
Observations show that Arctic sea ice extent has declined over the past several decades, and that this decline has accelerated in recent years. However, climate models used in the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report underestimate the observed decrease in ice extent. Furthermore, Rampal et al. studied 13 IPCC models and find that the models underestimate Arctic sea ice thinning by about a factor of 4 on average.
In addition to thinning, observations show that Arctic sea ice is drifting more rapidly, but the researchers find that the climate models do not capture this drift acceleration. The authors note that in most of the models, sea ice drifts faster when it is thicker, contrary to observations, which show thinner ice drifting faster. Faster drift increases the rate at which ice flows out of the Arctic. The models' weak coupling between ice thickness and drift velocity partly explains the models' underestimation of ice area, thickness, and velocity trends.
The authors conclude that the failure of IPCC models to capture ice thickness and velocity trends suggests that the model projections of an ice-free summer in the Arctic by 2100 are actually too conservative.
Journal of Geophysical Research-Oceans, doi: 10.1029/2011JC007110, 2011
“IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline”
- P. Rampal
- Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA and Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS/Université Joseph Fourier, St Martin d'Hères, France;
- J. Weiss
- Laboratoire de Glaciologie et Géophysique de l'Environnement, CNRS/Université Joseph Fourier, St Martin d'Hères, France;
- C. Dubois
- Centre National de Recherches Météorologiques, Toulouse, France;
- J.-M. Campin
- Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
2. Changing climate increases algae and plankton in the Arctic
Climate change is leading to increased biological productivity in the coastal Arctic. As ice melts and recedes far from land, winds interact with open waters to increase the upwelling of nutrient-rich deep water and stimulate biological productivity. Tremblay et al. quantify these changes using both remote sensing and in situ observations in the coastal Beaufort Sea. They find that ice ablation and the combination of increased upwelling and greater light penetration into the water column during fall 2007 and summer 2008 increased the production of ice algae, phytoplankton, and zooplankton by 2 to 6 times.
Geophysical Research Letters, doi: 10.1029/2011GL048825, 2011
“Climate forcing multiplies biological productivity in the coastal Arctic Ocean”
- J.-É. Tremblay
- Département de Biologie and Québec-Océan, Université Laval, Quebec, Quebec, Canada;
- S. Bélanger
- Département de Géographie, Université du Québec à Rimouski, Rimouski, Quebec, Canada;
- D. G. Barber and M. Asplin
- Centre for Earth Observation Science, Faculty of Environment, Earth and Resources, University of Manitoba, Winnipeg, Manitoba, Canada;
- J. Martin, G. Darnis, and L. Fortier
- Département de Biologie and Québec-Océan, Université Laval, Quebec, Quebec, Canada;
- Y. Gratton
- Eau, Terre et Environnement, Institut National de la Recherche Scientifique, Quebec, Quebec, Canada;
- H. Link, P. Archambault, and A. Sallon
- Institut des Sciences de la Mer de Rimouski, Université du Québec à Rimouski, Rimouski, Quebec, Canada;
- C. Michel
- Freshwater Institute, Fisheries and Oceans Canada, Winnipeg, Manitoba, Canada;
- W. J. Williams
- Institute of Ocean Sciences, Sidney, British Columbia, Canada;
- B. Philippe and M. Gosselin
- Institut des Sciences de la Mer de Rimouski, Université du Québec à Rimouski, Rimouski, Quebec, Canada.
3. Tracking contributors to sea-level rise
Various factors contribute to sea-level rise, including changing groundwater storage, thermal expansion of the oceans, and melting glaciers and ice sheets. However, studies that add up the observed contributions from these effects have not been able to account for the entire observed sea-level rise over the past several decades. To help resolve the discrepancy, Church et al. revisit sea-level budgets, considering sea-level and Earth's energy budgets together using new and updated estimates of all contributing factors for the past several decades, including a new estimate of groundwater depletion. They are able to close the sea-level budget from 1972 to the present. They find that thermal expansion contributed about 40 percent of observed rise since 1972 and that the sum of thermal expansion and glacier melting explains about 75 percent of sea-level rise since 1972. The remainder is from changes in ice sheets and terrestrial storage.
Ocean heat content changes are also required to understand the Earth's energy budget, which the authors also review. They find that about 90 percent of Earth's energy increase in recent decades went to warming the oceans. Over the past decade, there was little surface warming, although greenhouse gases continued to rise, ocean heat content increased, and sea level rose. Increased sulfur emissions, especially from developing countries, as well as aerosol from volcanic eruptions, are inferred to have acted as a negative forcing, slightly offsetting the warming caused by greenhouse gases.
Geophysical Research Letters, doi: 10.1029/2011GL048794, 2011
“Revisiting the Earth's sea-level and energy budgets from 1961 to 2008”
- John A. Church and Neil J. White
- Centre for Australian Weather and Climate Research and Wealth from Oceans Flagship, CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia;
- Leonard F. Konikow
- U.S. Geological Survey, Reston, Virginia, USA;
- Catia M. Domingues
- Antarctic Climate and Ecosystems Cooperative Research Centre, CSIRO Marine and Atmospheric Research, Aspendale, Victoria, Australia;
- J. Graham Cogley Department of Geography, Trent University, Peterborough, Ontario, Canada;
- Eric Rignot
- Department of Earth System Science, University of California, Irvine, California, USA and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA;
- Jonathan M. Gregory
- NCAS-Climate, Department of Meteorology, University of Reading, Reading, UK and Met Office Hadley Centre, Exeter, UK;
- Michiel R. van den Broeke
- Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands;
- Andrew J. Monaghan
- National Centre for Atmospheric Research, Boulder, Colorado, USA;
- Isabella Velicogna
- Department of Earth System Science, University of California, Irvine, California, USA and Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA.
4. Lakes an important source of carbon emissions
Around the world, vast detector networks track the transfer of carbon as it flows through the ecosystem, moving among the atmosphere, terrestrial surface, and organic matter. These carbon flux measurements are integral to understanding the role of various ecosystem components in the global carbon cycle and to performing accurate carbon accounting. But when precipitation or other processes pull large volumes of organic matter from the land into nearby lakes, this carbon effectively disappears from the carbon budget if gas fluxes over the lake surface are ignored, which they traditionally have been.
Using eddy covariance measurements, Huotari et al. track the flow of carbon into and out of Lake Valkea-Kotinen in southern Finland from the spring of 2003 until the autumn of 2007. They find that the lake was a net source of carbon, emitting between 70 and 100 grams of carbon per square meter per year (between 2 and 3 ounces carbon per square yard per year). When compared against the role of the surrounding forest, which was a net carbon sink, the lak's emissions were enough to offset about 10 percent of the forest's annual carbon storage. The authors find that the strongest controlling factor on the lake carbon emission rate was the stability of the lake's temperature stratification. Strong winds, heavy precipitation, and seasonal changes that increase water mixing were linked to stronger carbon fluxes.
Geophysical Research Letters, doi: 10.1029/2011GL048753, 2011
“Long-term direct CO2 flux measurements over a boreal lake: Five years of eddy covariance data”
- Jussi Huotari
- Lammi Biological Station, University of Helsinki, Lammi, Finland;
- Anne Ojala and Elina Peltomaa
- Department of Environmental Sciences, University of Helsinki, Lahti, Finland;
- Annika Nordbo and Timo Vesala
- Department of Physics, University of Helsinki, Helsinki, Finland;
- Samuli Launiainen
- Department of Physics, University of Helsinki, Helsinki, Finland and Finnish Forest Research Institute, Joensuu, Finland;
- Jukka Pumpanen, Terhi Rasilo and Pertti Hari
- Department of Forest Sciences, University of Helsinki, Helsinki, Finland.
5. Climate models' historical accuracy no guarantee of future success
To validate and rank the abilities of complex general circulation models (GCMs), emphasis has been placed on ensuring that they accurately reproduce the global climate of the past century. But because multiple paths can be taken to produce a given result, a model may get the right result but for the wrong reasons. Following this line of thinking, Crook and Forster analyze the construction of 11 atmosphere-ocean coupled GCMs. Rather than looking at the models’ reproductions of twentieth-century global average temperatures, which tend to perform well on all counts, the authors break the models' results into their re-creation of average, Arctic, and tropical climates. Further, they analyze the models' treatment of climate forcings (such as solar activity), feedback systems (like Arctic ice melt or the effects of clouds), and representations of heat storage and transport mechanisms.
The authors find that of the 11 models analyzed, 8 have global average, Arctic, and tropical temperatures that fall within an acceptable range of historical temperature observations for the past century. However, most are unable to capture a warming period that occurred in the 1920s and 1930s. Three models fall outside of the researchers' limits for acceptable historical accuracy. The authors also suggest that two additional models have warming profiles that unrealistically emphasize either Arctic or tropical temperature change. Because the models each use different weightings to describe the influence of various feedback systems and climate forcings, the researchers suggest that higher accuracy in reproducing historical observations is not an assurance that they will be more accurate in predicting future climate. They suggest that the problem lies not necessarily with the models but rather with the understandings of some forcing and feedback mechanisms being only loosely constrained. They suggest that effort should be placed on determining physically accurate representations of aerosol forcing to refine future models.
Journal of Geophysical Research-Atmospheres, doi: 10.1029/2011JD015924, 2011
“A balance between radiative forcing and climate feedback in the modeled 20th century temperature response”
- Julia A. Crook and Piers M. Forster
- School of Earth and Environment, University of Leeds, Leeds, UK.
6. Earthquake visualization shows ground motion in real time
On 11 March 2011 a magnitude 9.0 earthquake shattered the seabed off the eastern coast of Japan's Honshu Island. Drawing on the three-dimensional position records of a dense web of high-frequency GPS ground receiver stations, Grapenthin and Freymueller have developed animations of the abrupt horizontal and vertical motions that pulled parts of the country over 4 meters (13 feet) to the east and sank large portions of its eastern shore more than half a meter (1.6 feet) into the sea.
The researchers suggest that their animations (which can be seen online in the study's auxiliary material) are more intuitive than other forms of earthquake data visualization. Visualizations showing the peaks of a seismograph or maps overlain with the locations and magnitudes of the earthquake and its numerous aftershocks have been used to help explain the devastation to the public. While dramatic, such displays can be difficult for the public to interpret clearly because people often have trouble trying to picture what the recordings of a seismograph might look like on the ground. Members of the public could also have trouble understanding the logarithmic relationship between earthquake magnitude and energy.
In addition to the new visualizations' promising explanatory power, the authors suggest that the GPS stations’ real-time displacement measurements could, if automated, provide valuable scientific information that could be potentially useful in earthquake early warning systems or in tsunami and aftershock risk estimation.
Geophysical Research Letters, doi: 10.1029/2011GL048405, 2011
“The dynamics of a seismic wave field: Animation and analysis of kinematic GPS data recorded during the 2011 Tohoku-oki earthquake, Japan”
- Ronni Grapenthin and Jeffrey T. Freymueller
- Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska, USA.