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Jeffrey Park and Michael E. Mann

atmosphere/sea-surface temperature could be due to long-term variations in the exchange of heat with the ocean. The timing and characteristics of the 20th century ENSO episodes listed in Table 1 can be used to argue for a scenario by which this exchange occurs. In the early and middle decades of the 20th century, successive ENSO episodes are associated with increasing peak-to-peak projection onto global and hemispheric mean temperature, up to the point where secular warming commences, approximately at

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Weiyue Zhang, Zhongfeng Xu, and Weidong Guo

as Europe and North America, LULCC can result in a surface temperature cooling of 1° to 2°C primarily because of the increased land surface albedo ( Brovkin et al. 1999 ; Betts et al. 2007 ; Oleson et al. 2004 ; Bala et al. 2007 ; Davin and de Noblet-Ducoudré 2010 ; de Noblet-Ducoudré et al. 2012 ). Lawrence and Chase (2010) found that land-cover change results in a widespread regional warming and drying of the near-surface atmosphere but has a limited global influence on near

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Maria de Fátima F. L. Rasera, Maria Victoria R. Ballester, Alex V. Krusche, Cleber Salimon, Letícia A. Montebelo, Simone R. Alin, Reynaldo L. Victoria, and Jeffrey E. Richey

Introduction Rivers receive and process carbon from their watersheds, reflecting both natural and anthropogenic processes in the drainage basins. While in transit, the composition and concentration of various carbon fractions (organic and inorganic, particulate and dissolved) are modified by metabolic processes within the river channel, and part of the inorganic carbon may be outgassed to the atmosphere as CO 2 . Recent studies in temperate ecosystems indicate that the magnitude of CO 2

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Jean-Sébastien Landry, Navin Ramankutty, and Lael Parrott

1. Introduction Each grid cell in coupled climate–terrestrial vegetation models is bound to include major spatial heterogeneities that span various orders of magnitude and influence the processes represented ( Giorgi and Avissar 1997 ). The basic approaches accounting for subgrid cell heterogeneity in these models can be divided into two main categories. The composite (also named aggregated) approach computes land–atmosphere exchanges as a function of a single “representative” state of the grid

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A. D. McGuire, J. E. Walsh, J. S. Kimball, J. S. Clein, S. E. Euskirchen, S. Drobot, U. C. Herzfeld, J. Maslanik, R. B. Lammers, M. A. Rawlins, C. J. Vorosmarty, T. S. Rupp, W. Wu, and M. Calef

Introduction Global surface air temperature has warmed substantially since the middle of the nineteenth century ( Jones and Moberg 2003 ). This warming has been particularly strong in all latitudinal regions since about 1980 ( Alley et al. 2003 ; Johannessen et al. 2004 ). Between 1970 and 2000, surface air temperature over terrestrial regions between 50° and 70°N has increased approximately 0.35°C decade −1 ( McGuire et al. 2006 ; Euskirchen et al. 2007 ). The recent warming in high

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Kevin G. Harrison, Richard J. Norby, Wilfred M. Post, and Emily L. Chapp

of the “missing sink.” Using measurements of stable carbon isotopes in the atmosphere, Ciais et al. ( Ciais et al.1995 ) have shown that the terrestrial biosphere removed about half of fossil fuel emissions in 1992 and 1993, or about 3.5 Gt C yr −1 from the atmosphere. Using atmospheric oxygen measurements, Keeling et al. ( Keeling et al. 1996 ) have shown that the terrestrial biosphere sequestered about 2.0 ± 0.9 Gt C yr −1 (about one-third of fossil fuel input) from 1991 to 1994. Because

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Franz X. Faust, Cristóbal Gnecco, Hermann Mannstein, and Jörg Stamm

activity in the so-called Maunder Minimum indicating a reduced solar radiation has been claimed by Eddy ( Eddy 1976 ) to be responsible, but this does not explain the regional distribution. Volcanic activity might be another explanation: volcanic eruptions send particulate matter and SO 2 into the atmosphere, enhancing the aerosol load. This reduces the incoming solar radiation. Such events show up as relatively short cold periods, which add up in times of high volcanic activity. Prominent examples

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Geovane Webler, Débora Regina Roberti, Santiago Vianna Cuadra, Virnei Silva Moreira, and Marcos Heil Costa

1. Introduction The environmental impacts of agriculture systems have been extensively discussed by scientists and decision makers (e.g., Solomon et al. 2007 ). However, there is no consensus regarding the net contribution of agricultural areas to the net carbon exchange between the land surface and the atmosphere. Recent studies present different conclusions about the role of agroecosystems as a carbon source or sink ( Verma et al. 2005 ; Hollinger et al. 2005 ), generating further

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C. Kendra Gotangco Castillo and Kevin Robert Gurney

al. 2007 ), thus driving biosphere–atmosphere dynamics ( Barker et al. 2007 ). International negotiations for a post-2012 climate policy infrastructure are considering a wider role for the agriculture, forestry, and other land-use (AFOLU) sector in climate change mitigation ( Hassan et al. 2005 ). The 2010 Cancun agreements specifically call for the establishment of enhanced mechanisms for Reducing Emissions from Deforestation and Forest Degradation (REDD). REDD has driven the need for more

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Tristan Ballard, Richard Seager, Jason E. Smerdon, Benjamin I. Cook, Andrea J. Ray, Balaji Rajagopalan, Yochanan Kushnir, Jennifer Nakamura, and Naomi Henderson

and subsequent farm bills included a provision referred to as “Swampbuster,” which greatly restricts future tillage projects ( Gleason et al. 2011 ). Monitoring and enforcement of the rules have not been vigorous, however, and demand for biofuels is renewing interest in agricultural development ( Johnson et al. 2008 ; Johnston 2013 ). Additionally, PPR potholes are important carbon sinks, and drainage of wetlands leads to rapid releases of CO 2 to the atmosphere ( Badiou et al. 2011

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