Biogeosciences [B]

 CC:714B  Tuesday  1400h

Biogeosciences Fellows: Issues and Epiphanies

Presiding:  J Harden, USGS; W Schlesinger, Cary Institute of Ecosystem Studies


Transformation of the Land Surface: The Intertwining of Ecological, Atmospheric, and Social Dimensions

* DeFries, R (, Columbia University, 1200 Amsterdam Avenue, New York, NY 10027, United States

Modification to the land surface is one of the primary means through which the human enterprise obtains food, water, and other ecosystem services. Many unintended consequences result from land use transformations, including greenhouse gas emissions, modifications in exchanges of energy and water with the atmosphere, changes in disease vectors, and alterations of hydrologic flows. Tropical forests, one of the last remaining frontiers for agricultural expansion, are currently undergoing rapid transformation. The drivers of deforestation have shifted since prior decades from small-scale landholders to international demand for agricultural products. The impact on climate through carbon emissions from deforestation is currently at the heart of international policy discussions. The combination of ecological, atmospheric, and social dimensions to study deforestation is one illustration of the need for interdisciplinary approaches. AGU has been a leading force in incorporating biological sciences in the study of the earth system. Further evolution needs to include rigorous inclusion of anthropogenic processes in the study of the earth system.


Peak Oil, Peak Coal and Climate Change

* Murray, J W (, University of Washington, School of Oceanography Box 355351, Seattle, WA 98195-5351, United States

Research on future climate change is driven by the family of scenarios developed for the IPCC assessment reports. These scenarios create projections of future energy demand using different story lines consisting of government policies, population projections, and economic models. None of these scenarios consider resources to be limiting. In many of these scenarios oil production is still increasing to 2100. Resource limitation (in a geological sense) is a real possibility that needs more serious consideration. The concept of 'Peak Oil' has been discussed since M. King Hubbert proposed in 1956 that US oil production would peak in 1970. His prediction was accurate. This concept is about production rate not reserves. For many oil producing countries (and all OPEC countries) reserves are closely guarded state secrets and appear to be overstated. Claims that the reserves are 'proven' cannot be independently verified. Hubbert's Linearization Model can be used to predict when half the ultimate oil will be produced and what the ultimate total cumulative production (Qt) will be. US oil production can be used as an example. This conceptual model shows that 90% of the ultimate US oil production (Qt = 225 billion barrels) will have occurred by 2011. This approach can then be used to suggest that total global production will be about 2200 billion barrels and that the half way point will be reached by about 2010. This amount is about 5 to 7 times less than assumed by the IPCC scenarios. The decline of Non-OPEC oil production appears to have started in 2004. Of the OPEC countries, only Saudi Arabia may have spare capacity, but even that is uncertain, because of lack of data transparency. The concept of 'Peak Coal' is more controversial, but even the US National Academy Report in 2007 concluded only a small fraction of previously estimated reserves in the US are actually minable reserves and that US reserves should be reassessed using modern methods. British coal production can be used as a case study for testing the applicability the Linearization Model approach. This model has been applied to the various world regions by D. Rutledge (Cal Tech). The regions are summed to estimate global production. The conclusion is that the world's coal resources may be much less (maybe by 10 times) than assumed by the IPCC scenarios. Several research groups, including K. Aleklett (Uppsala), the Energy Watch Group and the Institute of Energy (IFE) and have independently reached the same conclusion. Simulations by D. Rutledge of atmospheric CO2 levels, using these values of ultimate oil and coal production as an input, suggest that atmospheric CO2 could reach maximum concentrations as low as 450 ppm. While some of these conclusions are controversial, available data clearly suggest that resource limitation should be given serious consideration in future climate change scenarios. There are also serious implications for economic recovery and energy security as well.


What Have We Learned After Several Decades of Gas Exchange-Wind Speed Relationships?

* Wanninkhof, R (, NOAA/AOML, 4301 Rickenbacker Causeway, Miami, FL 33149, United States

Relationships between gas transfer velocities and air-sea gas exchange provide a unique way to estimate gas fluxes from differences in gas concentrations between seawater and air. Moreover, since there are observational and modeling means to estimate patterns of air-sea disequilibrium of gases on spatial scales ranging from local to global, and temporal scales daily to decades, the relationships and wind speeds obtained from platforms, assimilation models or satellite provide the gas fluxes on these ranges of scales. With the need to constrain the global cycles of climate relevant gases such as carbon dioxide (CO2) and dimethyl sulfide (DMS), there has been keen interest in establishing robust relationships of gas transfer and wind speed. Most commonly used relationships are empirical and are developed with field measurements or global constraints with a functional form either based on a best fit or from basic understanding of surface forcing of gas transfer. There has been a convergence of these disparate methods at intermediate wind speeds. However, significant questions remain regarding the forcing of gas transfer at low and high winds, and if wind is the appropriate parameter to scale air-water disequilibria of gases to flux. Here I'll provide a "historical" overview of the merits of gas transfer velocities to estimate air-sea CO2 fluxes and outstanding questions.


Stream Ecosystem Responses to a Severe Spring Freeze: Unexpected Effects of Climate Change

* Mulholland, P J (, Oak Ridge National Laboratory, Environmental Sciences Division, ORNL, PO Box 2008, Oak Ridge, TN 37831-6036, United States
Roberts, B J (, Louisiana Universities Marine Consortium, 8124 Highway 56, Chauvin, LA 70344, United States
Hill, W R (, University of Illinois, Institute of Natural Resource Sustainability, University of Illinois, 1816 S. Oak Street, Champaign, IL 61820, United States
Smith, J G (, Oak Ridge National Laboratory, Environmental Sciences Division, ORNL, PO Box 2008, Oak Ridge, TN 37831-6036, United States

Some expected changes in climate resulting from human greenhouse gas emissions are clear and well documented, but others may be harder to predict because they involve extreme weather events or heretofore unusual combinations of weather patterns. A recent example of unusual weather that may become more frequent with climate change occurred in early spring 2007 when a large Arctic air mass moved into the central and eastern United States following a very warm late winter. We documented effects of this freeze event on Walker Branch, a well-studied stream ecosystem in eastern Tennessee. The 2007 spring freeze killed newly emerged leaves in the forest canopy, dramatically increasing the amount of light reaching the stream. Measurements of photosynthetically active radiation (PAR), gross primary production (GPP), nitrate uptake, and growth of a dominant herbivore, the snail Elimia clavaeformis, were made during the spring and summer months after the freeze and compared with measurements made over the same months in years before the freeze. PAR at the stream surface was sustained at levels considerably above those normal for the late spring and summer months due to incomplete recovery of forest canopy leaf area following the freeze. Increased PAR caused a cascade of ecological effects in the stream. GPP was considerably higher (2-3 times) during the late spring and summer months when normally low light levels severely limit stream GPP. Higher rates of stream GPP in turn caused higher rates of nitrate uptake by the autotrophic community and lower nitrate concentrations in stream water. The higher rates of stream GPP also resulted in higher snail growth rates. Net nitrate uptake and snail growth rates are typically zero to negative during summer; however, in 2007 they were maintained at moderate levels. These results show how changes in forest vegetation phenology, a predicted consequence of global warming, can have dramatic effects on stream productivity at multiple trophic levels and on nutrient cycling due to tight coupling of forest and stream ecosystems. Future climate-induced changes in canopy structure and phenology may lead to significant effects on stream ecosystems. Our results also show the value of long-term research for the detection of climate change effects on ecosystems.


Decisions, Decisions: Exotic Grass Invasions and Altered Wildfire Regimes in the American Deserts

* Betancourt, J L (, University of Arizona, 1955 E. 6th St., Tucson, AZ 85719, United States
* Betancourt, J L (, U.S. Geological Survey, 1955 E. 6th St., Tucson, AZ 85719, United States

Large-scale invasions by Eurasian and African grasses, brought in by chance or to feed cattle and control erosion, have introduced frequent and extensive fires into American deserts that supported little or no burning in the pre-European era. Based on the fossil record, these have been the fastest, most pervasive and transforming plant invasions of the last 10,000 years. They could easily accelerate with warmer and drier winters and longer and hotter growing seasons in the American West, conspicuous since the mid-1980's and projected to persist with global warming. In cool seasons and wet years that are not usually conducive to wildfires, these invasions are now driving long ignition fronts across long stretches of desertscrub into adjoining woodlands and forests. As such, invasive grasses are capable of changing fire-climate dynamics and altering the entire landscape mosaic. We must now choose between saving the desert or resigning ourselves to these novel and combustible grasslands. In either case, the first line of defense is to immediately adopt an aggressive program of fire suppression in our deserts at a time when we can barely afford to put out forest fires. In the American deserts and adjoining ecosystems, we are standing on a threshold and must now prepare the public for the consequences should those mitigation efforts fail. Both science and management needs should be prioritized to make the best use of limited funding and resources, taking into account the exponential growth of invader abundance, fuel connectivity and fire size as well as projected changes in land use and climate. What is missing is an integrated scientific and political framework vetted and approved by a wide range of stakeholders, with a good chance of sustainable and broadscale success. What decisions must we make, who makes them, and how will they be implemented across complex physical and cultural landscapes? My own take on these issues is that of a federal scientist with a sense of place and an ongoing crusade to engage the private and public sectors in Southern Arizona, where buffelgrass now threatens to convert a turistic Sonoran Desert into a burning savanna. Many of the lessons learned apply to other other pressing and spatially-extensive environmental problems.