This is a pre-print version of an article published in Nature Energy.

Modifications to the surface albedo through the deployment of cool roofs and pavements (reflective materials) and photovoltaic arrays (low reflection) have the potential to change radiative forcing, surface temperatures, and regional weather patterns. In this work we investigate the regional climate and radiative effects of modifying surface albedo to mimic massive deployment of cool surfaces (roofs and pavements) and, separately, photovoltaic arrays across the United States. We use a fully coupled regional climate model, the Weather Research and Forecasting (WRF) model, to investigate feedbacks between surface albedo changes, surface temperature, precipitation and average cloud cover. With the adoption of cool roofs and pavements, domain-wide annual average outgoing radiation increased by 0.16 ± 0.03 W m −2 (mean ± 95% C.I.) and afternoon summertime temperature in urban locations was reduced by 0.11-0.53 • C, although some urban areas showed no statistically significant temperature changes. In response to increased urban albedo, some rural locations showed summer afternoon temperature increases of up to +0.27 • C and these regions were correlated with less cloud cover and lower precipitation. The emissions offset obtained by this increase in outgoing radiation is calculated to be 3.3 ± 0.5 Gt CO 2 (mean ± 95% C.I.). The hypothetical solar arrays were designed to be able to produce one terawatt of peak energy and were located in the Mojave Desert of California. To simulate the arrays, the desert surface albedo was darkened, causing local afternoon temperature increases of up to +0.4 • C. Due to the solar arrays, local and regional wind patterns within a 300 km radius were affected. Statistically significant but lower magnitude changes to temperature and radiation could be seen across the domain due to the introduction of the solar arrays. The addition of photovoltaic arrays caused no significant change to summertime outgoing radiation when averaged over the full domain, as interannual variation across the continent obscured more consistent local forcing.

PREFACEThis is one report in a series that explores the costs, benefits, and other impacts of state renewable portfolio standards (RPS), both retrospectively and prospectively. The terminology applied in this series does not align precisely with the traditional concepts of costs and benefits, but rather is a function of how RPS programs have often been evaluated in practice. In particular, this analysis series evaluates RPS programs in terms of the following:• RPS compliance costs represent the incremental cost of meeting RPS compliance obligations, from the perspective of the utility or other load-serving entity, compared to the costs that would have been borne in the absence of the RPS. RPS compliance costs may be negative, if the renewable electricity used for RPS compliance is less expensive to the utility than the alternatives.• Benefits, as analyzed in this report series, consist specifically of environmental benefits that accrue to society at large, rather than to individual utilities. In theory, such benefits may be negative, representing net environmental costs, if the renewable electricity used for RPS compliance leads to more harmful environmental impacts than it avoids.• Other impacts, in the form of resource transfers from one market participant or segment to another, are also evaluated. These other impacts may also entail net costs or benefits to society at large, but our analyses focus only on the gross impacts, not the net cost or benefit. This report, the second in the series, analyzes historical benefits and impacts of all state RPS policies, in aggregate, employing a consistent and well-vetted set of methods and data sets. The analysis focuses on three specific benefits: greenhouse gas emissions, air pollution, and water use. It also analyzes three other impacts: gross job additions, wholesale electricity market price suppression, and natural gas price suppression. These are an important subset, but by no means a comprehensive set, of all possible effects associated with RPS policies. These benefits and impacts are also subject to many uncertainties, which are described and, to the extent possible, quantified within the report.The present report is intended to help policymakers, RPS administrators, and other decision-makers gauge the potential significance of a number of key benefits and impacts from state RPS programs. By noting limitations, caveats, and uncertainties in these results, the report also seeks to highlight important methodological considerations to evaluating RPS benefits and impacts. This report does not, however, provide a complete picture, and comparable information on both the costs and benefits, as well as other impacts, are ultimately needed to inform decision-making. To that end, a third report in this series is planned for the coming year to evaluate the future costs, benefits, and other impacts of state RPS policies, under both current policies and possible revisions. A prior study ) and subsequent update in this report series found that RPS compliance costs over the 2...

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We present a new, spatially resolved inventory of methane (CH4) emissions based on US-EPA emission factors and publically available activity data for 2010 California petroleum production and natural gas production, processing, transmission, and distribution. Compared to official California bottom-up inventories, our initial estimates are 3 to 7 times higher for the petroleum and natural gas production sectors but similar for the natural gas transmission and distribution sectors. Evidence from published "top-down" atmospheric measurement campaigns within Southern California supports our initial emission estimates from production and processing but indicates emission estimates from transmission and distribution are low by a factor of approximately 2. To provide emission maps with more accurate total emissions we scale the spatially resolved inventory by sector-specific results from a Southern California aircraft measurement campaign to all of California. Assuming uncertainties are determined by the uncertainties estimated in the top-down study, our estimated state total CH4 emissions are 541 ± 144 Gg yr(-1) (as compared with 210.7 Gg yr(-1) in California's current official inventory), where the majority of our reported uncertainty is derived from transmission and distribution. We note uncertainties relative to the mean for a given region are likely larger than that for the State total, emphasizing the need for additional measurements in undersampled regions.