CO2 Mitigation by Agriculture: An Overview

Agriculture currently contributes significantly to the increase of CO2 in the atmosphere, primarily through the conversion of native ecosystems to agricultural uses in the tropics. Yet there are major opportunities for mitigation of CO2 and other greenhouse gas emissions through changes in the use and management of agricultural lands. Agricultural mitigation options can be broadly divided into two categories: (I) strategies to maintain and increase stocks of organic C in soils (and biomass), and (ii) reductions in fossil C consumption, including reduced emissions by the agricultural sector itself and through agricultural production of biofuels to substitute for fossil fuels.Reducing the conversion of new land to agriculture in the tropics could substantially reduce CO2 emissions, but this option faces several difficult issues including population increase, land tenure and other socio-political factors in developing countries. The most significant opportunities for reducing tropical land conversions are in the humid tropics and in tropical wetlands. An important linkage is to improve the productivity and sustainability of existing agricultural lands in these regions.Globally, we estimate potential agricultural CO2 mitigation through soil C sequestration to be 0.4-0.9 Pg C y-1, through better management of existing agricultural soils, restoration of degraded lands, permanent "set-asides" of surplus agricultural lands in temperate developed countries and restoration of 10-20% of former wetlands now being used for agriculture. However, soils have a finite capacity to store additional C and therefore any increases in C stocks following changes in management would be largely realized within 50-100 years.Mitigation potential through reducing direct agricultural emissions is modest, 0.01-0.05 Pg C y-1. However, the potential to offset fossil C consumption through the use of biofuels produced by agriculture is substantial, 0.5-1.6 Pg C y-1, mainly through the production of dedicated biofuel crops with a smaller contribution (0.2-0.3 Pg C y-1) from crop residues.Many agricultural mitigation options represent "win-win" situations, in that there are important side benefits, in addition to CO2 mitigation, that could be achieved, e.g. improved soil fertility with higher soil organic matter, protection of lands poorly suited for permanent agriculture, cost saving for fossil fuel inputs and diversification of agricultural production (e.g. biofuels). However, the needs for global food production and farmer/societal acceptability suggest that mitigation technologies should conform to: (I) the enhancement of agricultural production levels in parts of the world where food production and population demand are in delicate balance and (ii) the accrual of additional benefits to the farmer (e.g., reduced labor, reduced or more efficient use of inputs) and society at large.     

Sea-Spray-Generation Dependence on Wind and Wave Combinations: A Laboratory Study

Boundary-Layer Meteorology - We investigate the effects of wind–wave interactions on the surface sea-spray-generation flux. To this end, the Marine Aerosol Tunnel Experiment (MATE2019) was...     

Development of a non-linear mixed spectral finite difference model for turbulent boundary-layer flow over topography

Further development of the non-linear mixed spectral finite difference (NLMSFD) model of turbulent boundary-layer flow over topography is documented. This includes modifications and refinements to the solution procedure, the incorporation of second-order turbulence closures to the model and the three-dimensional extension of the model. Based on these higher order closures, linear limitations, boundary-layer approximation and non-linear effects are discussed. The impact of different turbulence closures on the prediction of the NLMSFD model is also demonstrated. Furthermore, sample results for 3D idealized topography (sinusoidal) are presented. The parameterization of drag over small-scale topography is also addressed.     

Quasi-Wavelet Model of Von Kármán Spectrum of Turbulent Velocity Fluctuations

The von Kármán spectra of turbulent temperature andvelocity fluctuations have been widely used in the literature on turbulenceand electromagnetic, seismic, and acoustic wave propagation in random media.In this paper we provide a phenomenological motivation for the vonKármán velocity spectrum in terms of the quasi-wavelet model ofturbulence developed recently. In this model, turbulence is represented as asuperposition of self-similar localized eddies of many different scales. Wefind a functional form for these eddies that yields the von Kármán velocity spectrum exactly. We also show that other eddy functions producevelocity spectra that have the same general form as the von Kármán spectrum, and we consider possible quasi-wavelet representations of the`Kansas' spectrum and the `-1' spectrum. We also present asystematic determination, based on turbulence similarity theories, of theparameters of the von Kármán spectra of temperature and velocityfluctuations in an unstable atmospheric boundary layer.     

Author Index

Authors Index

Author Index     

When is it appropriate to combine expert judgments?

Summary Rather than seeking improved methodologies, difficulty in combining expert opinion should serve as a warning flag that causes us to seek alternative modes of policy analysis. These alternatives are usually more appropriate for the real audience for our analyses.Policy analysis of climate change is too often framed in terms that amount to preparing the tools with which a benevolent world dictator could do cost-benefit analysis. This tends to overemphasize end-to-end analysis that must rely on the combined opinions of experts. This framing is unrealistic and encourages omission of important aspects of the climate problem such as its heterogeneity. Rejecting this framing in favor of alternate, less all encompassing, forms of policy analysis permits more robust results, and reduces the emphasis on combining expert opinion.While the opinions expressed here are my own, I thank Hadi Dowlatabadi, M. Granger Morgan, Ted Parson, and James Risbey for their perceptive comments.     

Spatial Discontinuities in Support for Hydraulic Fracturing: Searching for a “Goldilocks Zone”

Recent research suggests that those located closer to energy development are, on average, more supportive of this development. However, case studies in specific locations reveal additional nuance. In a case study of Bakken Shale residents, Junod et al. identified a “Goldilocks Zone” of unconventional oil and gas development (UOGD) acceptance—an area on the periphery of development that is “just right” because residents feel close enough to receive economic benefits but far enough away to avoid negative impacts. We explore whether this Goldilocks Zone extends nationally by combining geocoded public opinion data (N?=?23,154) with UOGD locations. Using multilevel regression modeling, we find that respondents located within 115?km of newly active UOGD are more supportive of hydraulic fracturing while those located within 115–305?km are comparatively less supportive. While we do not uncover a national-level Goldilocks Zone, our work highlights innovative approaches for examining spatial relationships in energy development opinion.     

Quantifying different riverbank erosion processes during an extreme flood event

Riverbank erosion is a major contributor to catchment sediment budgets. At large spatial scales data is often restricted to planform channel change, with little information on process distributions and their sediment contribution. This study demonstrates how multi‐temporal LiDAR and high resolution aerial imagery can be used to determine processes and volumes of riverbank erosion at a catchment scale. Remotely sensed data captured before and after an extreme flood event, enabled a digital elevation model of difference (DoD) to be constructed for the channel and floodplain. This meant that: the spatial area that could be assessed was extensive; three‐dimensional forms of bank failures could be mapped at a resolution that enabled process inference; and the volume and rates of different bank erosion processes over time could be assessed. A classification of riverbank mass failures, integrating form and process, identified a total of 437 mass failure polygons throughout the study area. These were interpreted as wet flow mass failures based on the presence of a well defined scarp wall and the absence of failed blocks on the failure floor. The failures appeared to be the result of: bank exfiltration, antecedent moisture conditions preceding the event, and the historic development of the channel. Using one‐dimensional hydraulic modelling to delineate geomorphic features within the main boundary of the macrochannel, an estimated 1 466 322 m² of erosion was interpreted as fluvial entrainment, occurring across catchment areas from 30 to 1668 km². Only 8% of the whole riverbank planform area was occupied by mass failures, whilst fluvial entrainment covered 33%. A third of the volume of material eroded came from mass failures, even though they occupied 19% of the eroded bank area. The availability of repeat LiDAR surveys, combined with high‐resolution aerial photography, was very effective in erosion process determination and quantification at a large spatial scale. Copyright © 2013 John Wiley & Sons, Ltd.