A review of measurement-based assessments of the aerosol direct radiative effect and forcing

Aerosols affect the Earth's energy budget directly by scattering and absorbing radiation and indirectly by acting as cloud condensation nuclei and, thereby, affecting cloud properties. However, large uncertainties exist in current estimates of aerosol forcing because of incomplete knowledge concerning the distribution and the physical and chemical properties of aerosols as well as aerosol-cloud interactions. In recent years, a great deal of effort has gone into improving measurements and datasets. It is thus feasible to shift the estimates of aerosol forcing from largely model-based to increasingly measurement-based. Our goal is to assess current observational capabilities and identify uncertainties in the aerosol direct forcing through comparisons of different methods with independent sources of uncertainties. Here we assess the aerosol optical depth (τ), direct radiative effect (DRE) by natural and anthropogenic aerosols, and direct climate forcing (DCF) by anthropogenic aerosols, focusing on satellite and ground-based measurements supplemented by global chemical transport model (CTM) simulations. The multi-spectral MODIS measures global distributions of aerosol optical depth (τ) on a daily scale, with a high accuracy of ±0.03±0.05τ over ocean. The annual average τ is about 0.14 over global ocean, of which about 21%±7% is contributed by human activities, as estimated by MODIS fine-mode fraction. The multi-angle MISR derives an annual average AOD of 0.23 over global land with an uncertainty of ~20% or ±0.05. These high-accuracy aerosol products and broadband flux measurements from CERES make it feasible to obtain observational constraints for the aerosol direct effect, especially over global the ocean. A number of measurement-based approaches estimate the clear-sky DRE (on solar radiation) at the top-of-atmosphere (TOA) to be about -5.5±0.2 Wm-2 (median ± standard error from various methods) over the global ocean. Accounting for thin cirrus contamination of the satellite derived aerosol field will reduce the TOA DRE to -5.0 Wm-2. Because of a lack of measurements of aerosol absorption and difficulty in characterizing land surface reflection, estimates of DRE over land and at the ocean surface are currently realized through a combination of satellite retrievals, surface measurements, and model simulations, and are less constrained. Over the oceans the surface DRE is estimated to be -8.8±0.7 Wm-2. Over land, an integration of satellite retrievals and model simulations derives a DRE of -4.9±0.7 Wm-2 and -11.8±1.9 Wm-2 at the TOA and surface, respectively. CTM simulations derive a wide range of DRE estimates that on average are smaller than the measurement-based DRE by about 30-40%, even after accounting for thin cirrus and cloud contamination. A number of issues remain. Current estimates of the aerosol direct effect over land are poorly constrained. Uncertainties of DRE estimates are also larger on regional scales than on a global scale and large discrepancies exist between different approaches. The characterization of aerosol absorption and vertical distribution remains challenging. The aerosol direct effect in the thermal infrared range and in cloudy conditions remains relatively unexplored and quite uncertain, because of a lack of global systematic aerosol vertical profile measurements. A coordinated research strategy needs to be developed for integration and assimilation of satellite measurements into models to constrain model simulations. Enhanced measurement capabilities in the next few years and high-level scientific cooperation will further advance our knowledge.

Sources, sinks, and transatlantic transport of North African dust aerosol: a multimodel analysis and comparison with remote sensing data

This study evaluates model-simulated dust aerosols over North Africa and the North Atlantic from five global models that participated in the Aerosol Comparison between Observations and Models phase II model experiments. The model results are compared with satellite aerosol optical depth (AOD) data from Moderate Resolution Imaging Spectroradiometer (MODIS), Multiangle Imaging Spectroradiometer (MISR), and Sea-viewing Wide Field-of-view Sensor, dust optical depth (DOD) derived from MODIS and MISR, AOD and coarse-mode AOD (as a proxy of DOD) from ground-based Aerosol Robotic Network Sun photometer measurements, and dust vertical distributions/centroid height from Cloud Aerosol Lidar with Orthogonal Polarization and Atmospheric Infrared Sounder satellite AOD retrievals. We examine the following quantities of AOD and DOD: (1) the magnitudes over land and over ocean in our study domain, (2) the longitudinal gradient from the dust source region over North Africa to the western North Atlantic, (3) seasonal variations at different locations, and (4) the dust vertical profile shape and the AOD centroid height (altitude above or below which half of the AOD is located). The different satellite data show consistent features in most of these aspects; however, the models display large diversity in all of them, with significant differences among the models and between models and observations. By examining dust emission, removal, and mass extinction efficiency in the five models, we also find remarkable differences among the models that all contribute to the discrepancies of model-simulated dust amount and distribution. This study highlights the challenges in simulating the dust physical and optical processes, even in the best known dust environment, and stresses the need for observable quantities to constrain the model processes.

The role of Planning Aid England in supporting communities’ engagement in planning

In considering the position of community engagement within planning in a time of neo-liberalism and a context of ‘neo-communitarian localism’ (cf. Jessop, 2002; DeFilippis, 2004), this paper reviews the role and relevance of Planning Aid in terms of its performance and aspirations in guiding and transforming planning practice (Friedmann, 1973; 1987; 2011) since its inception in 1973. In doing this we reflect on the critiques of Planning Aid performance provided by Allmendinger (2004) and bring the account up-to-date following on from past considerations (e.g. Bidwell and Edgar, 1982; Thomas, 1992; Brownill and Carpenter, 2007a,b; Carpenter and Brownill, 2008) and prompted by the 35 years since the University of Reading produced the first published work reviewing Planning Aid (Curtis and Edwards, 1980). Our paper is timely given renewed attacks on planning, the implementation of a form of localism and reductions in funding for planning in a time of austerity. Our view is that the need for forms of ‘neo-advocacy’ planning and community development are perhaps even more necessary now, given the continuing under-representation of lower income groups, minority groups and to allow for the expression of alternative planning futures. Thus further consideration of how to ensure that Planning Aid functions are sustained and understood requires the attention of policymakers and the planning profession more widely.

Neo-Gramscianism

Gramscian concepts have been utilized by scholars to analyze and illuminate various aspects of GLOBAL ENVIRONMENTAL GOVERNANCE. A foremost application of neo-Gramscianism to the scholarship on global environmental governance has been in challenging the basic premise of orthodox regime theory that international environmental rule-making is the exclusive preserve of state actors. Gramscian theory is very sensitive to the role and importance of political contestations, accommodations and compromises, which many have noted as the ‘stuff’ of environmental governance. Crucially, while a Gramscian analysis is sensitive to the counter-hegemonic potential of the subordinate class and the ever contested and changing contours of power in a social regime, it does not subscribe to the unlimited possibility of outcome. Given the utility of neo-Gramscian ideas, as demonstrated by the scholarship discussed, it is surprising that the approach has not been deployed more widely in the scholarship on global environmental governance.

Business

This main argument of the chapter is that the explanation of the slow pace of business action requires a socio-cultural theory that transcends the narrow premises of dominant corporate social responsibility (CRS) and business management approaches. I assert that only a critical political economy approach which captures the complex interplay between cultural ideas, power, politics, and economic interests can provide basis for explaining the prospects and limits of corporate climate governance. My argument, which draws from similar existing works (Levy and Egan 2003, Levy and Newell 2005, Okereke et al. 2009) is focused on carbon-intensive multinational companies (MNCs) whose activities are generally considered crucial in shaping societal response to climate change (McKibben 2012).