Informative Interview Of John Gash In EOS On “Amazonia And Global Change”

There is a very informative interview of John Gash by Leslie Ofori in the September 21 2010 issue of EOS. The article is titled

Amazonia and Global Change

is based on the AGU monograph of the same name.

The article starts with the introduction

“The Large-Scale Biosphere- Atmosphere Experiment in Amazonia (LBA) is multidisciplinary international scientific project that seeks to understand the functioning of Amazonia as a unique ecosystem. The AGU monograph Amazonia and Global Change, edited by Michael Keller, Mercedes Bustamante, John Gash, and Pedro Silva Dias, synthesizes the results of the study. In this interview, Eos talks with micrometeorologist John Gash, who specializes in measuring and modeling evaporation from forests. He is a senior researcher in the Department of Hydrology and Geo- environmental Sciences at Vrije Universiteit Amsterdam”

and excerpts include the questions and answers [where I have highlighted key text]

Eos: One section of the book focuses on land use changes. How have land use and land cover in the Amazon region changed in recent years? What are the effects of land use and land cover change on the region? What is the impact of land use on the climate?

Gash: The deforestation of Amazonia has been proceeding seemingly inexorably since the early 1970s. Recent years have seen an acceleration of soya production, but cattle ranching still dominates managed lands. Both land uses completely replace the forest ecosystem. LBA has given us new understanding about the role of new roads and the development options for intensification rather than extensification of agriculture. Physically, deforestation changes the albedo (reflectivity) of the surface, the surface aerodynamic roughness, and the response to drought. While the deeper rooted trees continue to transpire and photosynthesize during the dry season, pasture grass and crops are dormant. This affects the balance between water and heat fluxes into the atmosphere, which in turn affects atmospheric boundary layer growth. Small- scale deforestation may lead to increased rainfall, but large- or basin- scale deforestation is expected to lead to less rain.

Eos: Another section of the book covers the atmosphere. How does the Amazon’s biosphere interact with the atmosphere?

Gash: The surface energy and water balance affects the thermodynamics and therefore the dynamics of the atmosphere. Changes in Amazon precipitation caused by land use change have been shown to interfere with climate patterns in areas as distant as Europe and North America. The emission of biogenic volatile organic compounds that form cloud nuclei affects rainfall generation, and increasing atmospheric carbon dioxide (CO2) may be increasing plant productivity. All these interactions change when forest is replaced by agriculture.

Eos: Does smoke from biomass fires have direct and indirect effects on the atmosphere? If so, what are those effects?

Gash: Yes, definitely. Smoke particles create a new regime of aerosols. In the wet season, when there is little burning, aerosol concentrations are very low and large cloud droplets form on naturally emitted organic condensation nuclei; but in the dry season, aerosols released during burning produce a large population of small droplets, which inhibits precipitation. These aerosols can be transported long distances from the source regions, and their effect may be significant over large areas. The dry season aerosol concentration also increases the amount of diffuse sunlight; this initially increases photosynthesis, but at high concentrations, photosynthesis is seriously diminished. Large-scale burning inhibits dry season rainfall.”

This interview is yet another example which documents that hypothesis 2b in our paper

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union

is rejected. Hypothesis 2b reads

Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.”

The only hypothesis that is consistent with the Gash interview is

Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first-order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern during the coming decades.

The 2007 IPCC clearly failed in properly testing the hypotheses that we present in our EOS paper. The next assessment, of course, has been made aware of this and we will see if they properly include this issue in their next assessment.

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