Modeling results incorporating several distinct urban expansion futures for the United States in 2100 show that, in the absence of any adaptive urban design, megapolitan expansion, alone and separate from greenhouse gas-induced forcing, can be expected to raise near-surface temperatures 1-2°C not just at the scale of individual cities but over large regional swaths of the country. This warming is a significant fraction of the 21st century greenhouse gas-induced climate change simulated by global climate models. Using a suite of regional climate simulations, we assessed the efficacy of commonly proposed urban adaptation strategies, such as green, cool roof, and hybrid approaches, to ameliorate the warming. Our results quantify how judicious choices in urban planning and design cannot only counteract the climatological impacts of the urban expansion itself but also, can, in fact, even offset a significant percentage of future greenhouse warming over large scales. Our results also reveal tradeoffs among different adaptation options for some regions, showing the need for geographically appropriate strategies rather than one size fits all solutions.sustainability | mitigation | land-use change | urbanization | urban climate

Biomass-derived energy offers the potential to increase energy security while mitigating anthropogenic climate change, but a successful path toward increased production requires a thorough accounting of costs and benefits. Until recently, the efficacy of biomass-derived energy has focused primarily on biogeochemical consequences. Here we show that the biogeophysical effects that result from hypothetical conversion of annual to perennial bioenergy crops across the central United States impart a significant local to regional cooling with considerable implications for the reservoir of stored soil water. This cooling effect is related mainly to local increases in transpiration, but also to higher albedo. The reduction in radiative forcing from albedo alone is equivalent to a carbon emissions reduction of 78 t C ha −1 , which is six times larger than the annual biogeochemical effects that arise from offsetting fossil fuel use. Thus, in the near-term, the biogeophysical effects are an important aspect of climate impacts of biofuels, even at the global scale. Locally, the simulated cooling is sufficiently large to partially offset projected warming due to increasing greenhouse gases over the next few decades. These results demonstrate that a thorough evaluation of costs and benefits of bioenergyrelated land-use change must include potential impacts on the surface energy and water balance to comprehensively address important concerns for local, regional, and global climate change.regional climate modeling | agriculture | landscape modification | CO2 S ecuring energy independence and lessening the human fingerprint on climate are two principal motivations behind increased production of bioenergy. Recognition of the full array of costs and benefits of increased production, such as effects on energy and food security, anthropogenic climate change mitigation, and maintenance of biodiversity, will assist in realization of principal objectives (1-8). Prior research gauging the effectiveness of bioenergy has estimated potential impacts based on greenhouse gas (GHG) emission changes through direct or indirect land-use change (LUC) and by means of life cycle analysis (LCA). In addition to impacts on GHGs, LUC also modifies the surface energy and water balance (9), with implications for near-surface temperature and precipitation, and serves as an additional first-order climate forcing on global (10, 11) and regional (9, 12) spatial scales.One of the main proposed strategies for bioenergy production is widespread planting and harvesting of perennial grasses, such as switchgrass (Panicum virgatum L.) or miscanthus (Miscanthus X giganteus). One LCA study suggested that net GHG savings relative to fossil fuels of greater than 200 g CO 2 e-C m −2 yr −1 may be expected for biomass (switchgrass) conversion to ethanol (13) (roughly double for hybrid poplar). Potential mitigation, however, is complicated by variability in inventory components and system boundaries (i.e., LCA methodology) that leads to GHG displacement estimates that diffe...

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This article investigates the effect of air conditioning (AC) systems on air temperature and examines their electricity consumption for a semiarid urban environment. We simulate a 10 day extreme heat period over the Phoenix metropolitan area (U.S.) with the Weather Research and Forecasting model coupled to a multilayer building energy scheme. The performance of the modeling system is evaluated against 10 Arizona Meteorological Network weather stations and one weather station maintained by the National Weather Service for air temperature, wind speed, and wind direction. We show that explicit representation of waste heat from air conditioning systems improved the 2 m air temperature correspondence to observations. Waste heat release from AC systems was maximum during the day, but the mean effect was negligible near the surface. However, during the night, heat emitted from AC systems increased the mean 2 m air temperature by more than 1°C for some urban locations. The AC systems modified the thermal stratification of the urban boundary layer, promoting vertical mixing during nighttime hours. The anthropogenic processes examined here (i.e., explicit representation of urban energy consumption processes due to AC systems) require incorporation in future meteorological and climate investigations to improve weather and climate predictability. Our results demonstrate that releasing waste heat into the ambient environment exacerbates the nocturnal urban heat island and increases cooling demands.

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