Saturday, June 19, 2010

Cheryl A. Palm et al., PNAS, Identifying potential synergies and trade-offs for meeting food security and climate change objectives in sub-Saharan Africa

Proc. Natl. Acad. Sci., p

Identifying potential synergies and trade-offs for meeting food security and climate change objectives in sub-Saharan Africa

 Cheryl A. Palm et al.

Abstract

Potential interactions between food production and climate mitigation are explored for two situations in sub-Saharan Africa, where deforestation and land degradation overlap with hunger and poverty. Three agriculture intensification scenarios for supplying nitrogen to increase crop production (mineral fertilizer, herbaceous legume cover crops—green manures—and agroforestry—legume improved tree fallows) are compared to baseline food production, land requirements to meet basic caloric requirements, and greenhouse gas emissions. At low population densities and high land availability, food security and climate mitigation goals are met with all intensification scenarios, resulting in surplus crop area for reforestation. In contrast, for high population density and small farm sizes, attaining food security and reducing greenhouse gas emissions require mineral fertilizers to make land available for reforestation; green manure or improved tree fallows do not provide sufficient increases in yields to permit reforestation. Tree fallows sequester significant carbon on cropland, but green manures result in net carbon dioxide equivalent emissions because of nitrogen additions. Although these results are encouraging, agricultural intensification in sub-Saharan Africa with mineral fertilizers, green manures, or improved tree fallows will remain low without policies that address access, costs, and lack of incentives. Carbon financing for small-holder agriculture could increase the likelihood of success of Reducing Emissions from Deforestation and Forest Degradation in Developing Countries programs and climate change mitigation but also promote food security in the region.

Link:  http://www.pnas.org/content/early/2010/06/16/0912248107.abstract

Wednesday, June 9, 2010

Hiroaki Kawase et al., GRL 37 (2010), Physical mechanism of long-term drying trend over tropical North Africa

Geophysical Research Letters, 37 (2010) L09706; doi: 10.1029/2010GL043038 

Physical mechanism of long-term drying trend over tropical North Africa

Hiroaki Kawase, Manabu Abe, Yukiko Yamada (National Institute for Environmental Studies, Tsukuba, Japan), Toshihiko Takemura (Research Institute for Applied Mechanics, Kyushu University, Fukuoka, Japan), Tokuta Yokohata (Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan) and Toru Nozawa (National Institute for Environmental Studies, Tsukuba, Japan)

Abstract

Based on an approximated moisture budget equation, we investigate the physical mechanisms of a drying trend observed over tropical North Africa in the boreal summer during the 20th Century by analyzing datasets of several climate-model experiments forced with various combinations of natural and anthropogenic forcings. Increased anthropogenic aerosols thermodynamically induce a drying trend due to a tropospheric cooling and dynamically induce an additional drying trend due to an atmospheric local circulation change stirred up by the strong gradient of a sea surface temperature anomaly over the tropical Atlantic Ocean. Increased greenhouse gases, on the other hand, induce a drying trend through the large-scale dynamic effect, which is canceled out by the thermodynamically induced moistening trend due to tropospheric warming. Therefore, the drying trend observed over tropical North Africa during the 20th Century is strongly affected by the increased anthropogenic aerosols through both the dynamic and thermodynamic effects. 

Received 4 March 2010; accepted 31 March 2010; published 11 May 2010.

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