Christopher P. Weaver

Urban adaptation can roll back warming of emerging megapolitan regions.

Significance Conversion to urban landforms has consequences for regional climate and the many inhabitants living within the built environment. The purpose of our investigation was to explore hydroclimatic impacts of 21st century urban expansion across the United States and examine the efficacy of commonly proposed urban adaptation strategies in context of long-term global climate change. We show that, in the absence of any adaptive urban design, urban expansion across the United States imparts warming over large regional swaths of the country that is a significant fraction of anticipated temperature increases resulting from greenhouse gas-induced warming. Adapting to urban-induced climate change is geographically dependent, and the robust analysis that we present offers insights into optimal approaches and anticipated tradeoffs associated with varying expansion pathways. 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.

Atmospheric Disturbances Caused by Human Modification of the Landscape

This study documents significant atmospheric effects over the U.S. central plains caused by human modification of the landscape. Using observations and an atmospheric model, it is shown here that diurnal, thermally induced circulations occur during summer over a 250 × 250 km region in Oklahoma and Kansas. Furthermore, it is shown that the driving force behind these circulations is the landscape heterogeneity resulting from differential land use patterns, that such atmospheric phenomena are characteristic of surfaces with this type of heterogeneity and not limited to infrequent days when unusual wind or other meteorological conditions prevail, and that the net effect of these motions is significant, not only locally, but also at the regional and global scales.

A preliminary synthesis of modeled climate change impacts on U.S. regional ozone concentrations.

This paper provides a synthesis of results that have emerged from recent modeling studies of the potential sensitivity of U.S. regional ozone (O3) concentrations to global climate change (ca. 2050). This research has been carried out under the auspices of an ongoing U.S. Environmental Protection Agency (EPA) assessment effort to increase scientific understanding of the multiple complex interactions among climate, emissions, atmospheric chemistry, and air quality. The ultimate goal is to enhance the ability of air quality managers to consider global change in their decisions through improved characterization of the potential effects of global change on air quality, including O3 The results discussed here are interim, representing the first phase of the EPA assessment. The aim in this first phase was to consider the effects of climate change alone on air quality, without accompanying changes in anthropogenic emissions of precursor pollutants. Across all of the modeling experiments carried out by the differe...

Improved Techniques for Evaluating GCM Cloudiness Applied to the NCAR CCM3

Abstract Evaluations of GCM cloudiness typically compare climatological output with observations, but averaging over time can obscure the presence of compensating errors. A more informative and stringent evaluation can be obtained by averaging cloud properties according to meteorological process (i.e., compositing). The present study illustrates this by comparing simulated and observed cloudiness composited on 500-mb pressure vertical velocity over the summertime midlatitude North Pacific. Observed cloud properties are daily ERBE cloud radiative forcing, daily NVAP liquid water path, and 3-hourly ISCCP cloud optical thickness and cloud-top pressure. ECMWF and NCEP–NCAR reanalyses provide vertical velocity. The GCM evaluated is the NCAR CCM3 with Rasch and Kristjansson (1998) predicted cloud condensate. Results show that CCM3 overproduces cloud optical thickness, cloud-top height, and cloud radiative forcing under conditions of synoptic ascent and underproduces cloud cover, cloud-top height, and cloud radi...

Variation in Estimated Ozone-Related Health Impacts of Climate Change due to Modeling Choices and Assumptions

Background: Future climate change may cause air quality degradation via climate-induced changes in meteorology, atmospheric chemistry, and emissions into the air. Few studies have explicitly modeled the potential relationships between climate change, air quality, and human health, and fewer still have investigated the sensitivity of estimates to the underlying modeling choices. Objectives: Our goal was to assess the sensitivity of estimated ozone-related human health impacts of climate change to key modeling choices. Methods: Our analysis included seven modeling systems in which a climate change model is linked to an air quality model, five population projections, and multiple concentration–response functions. Using the U.S. Environmental Protection Agency’s (EPA’s) Environmental Benefits Mapping and Analysis Program (BenMAP), we estimated future ozone (O3)-related health effects in the United States attributable to simulated climate change between the years 2000 and approximately 2050, given each combination of modeling choices. Health effects and concentration–response functions were chosen to match those used in the U.S. EPA’s 2008 Regulatory Impact Analysis of the National Ambient Air Quality Standards for O3. Results: Different combinations of methodological choices produced a range of estimates of national O3-related mortality from roughly 600 deaths avoided as a result of climate change to 2,500 deaths attributable to climate change (although the large majority produced increases in mortality). The choice of the climate change and the air quality model reflected the greatest source of uncertainty, with the other modeling choices having lesser but still substantial effects. Conclusions: Our results highlight the need to use an ensemble approach, instead of relying on any one set of modeling choices, to assess the potential risks associated with O3-related human health effects resulting from climate change.

Understanding the Meteorological Drivers of U.S. Particulate Matter Concentrations in a Changing Climate

Particulate matter (PM) air pollution is a serious public health issue for the United States. While there is a growing body of evidence that climate change will partially counter the effectiveness of future precursor emission reductions to reduce ozone (O3) air pollution, the links between PM and climate change are more complex and less understood. This paper discusses what we currently understand about the potential sensitivity of PM episodes to climate-change-related shifts in air pollution meteorology, in the broader context of the emissions and atmospheric chemistry drivers of PM. For example, initial studies have focused largely on annual average concentrations of inorganic aerosol species. However, the potential for future changes in the occurrence of PM episodes, and their underlying meteorological drivers, are likely more important to understand and remain highly uncertain. In addition, a number of other poorly understood factors interact with these likely critical meteorological changes. These in...

Toward a parameterization of mesoscale fluxes and moist convection induced by landscape heterogeneity

A growing body of evidence from modeling and observations indicates that mesoscale circulations generated by land-surface wetness heterogeneities result in substantial vertical fluxes of sensible heat and moisture. These fluxes are believed to have a strong impact on large-scale mean atmospheric variables such as temperature, humidity, cloudiness, and precipitation. Currently, however, this type of mesoscale convective process is not considered in general circulation models (GCMs). In this study, we develop a parameterization for these landscape-forced fluxes, similar to what might eventually be implemented into a GCM. In addition, we investigate the relationship between the parameterized mesoscale flux and the convective condensation associated with these circulations as a first step toward directly including clouds and precipitation forced by surface heterogeneity effects as one component of a comprehensive GCM convective scheme. To generate the data necessary for this development, we perform a number of simulations with a state-of-the-art mesoscale model to determine the sensitivity of the fluxes and condensation to a variety of background atmospheric conditions and land-surface wetness distributions. We use similarity theory to determine the dependence of the mesoscale sensible heat and moisture fluxes on the parameters relevant to the problem, and we create parameterized vertical flux profiles by fitting with Chebyshev polynomials. The parameterized fluxes are tested against an independent, three-dimensional (3-D) simulation of mesoscale development over a heterogeneous landscape, and general good agreement is found. We propose an empirical form for domain-averaged condensation on the basis of a linear relationship with parameterized mesoscale moisture flux and also demonstrate a reasonable agreement with the results from the 3-D simulation. The methodology of this study, i.e., the use of a numerical model in the preliminary stages of parameterization development, is advantageous for situations where the necessary observational data set is nonexistent. The use of model simulations to fully explore the parameter space of this type of problem should then lead to observational campaigns that focus on only those key processes and variables which are relevant for the further refinement of a given parameterization.

Sensitivity of model-simulated summertime precipitation over the Mississippi River Basin to the spatial distribution of initial soil moisture

[1] Using a numerical model, the Regional Atmospheric Modeling System (RAMS), we simulate July precipitation over parts of the Mississippi River Basin and surroundings for each of three years, 1995–1997, with six different initial soil moisture patterns: three (control, dry, and wet) with a realistic (observationally based) spatial distribution, and three (control, dry, and wet) with a horizontally homogeneous distribution. Our goal is to determine the impact on future simulated precipitation of changing the initial soil moisture spatial distribution. The spatially homogeneous initial soil moisture pattern represents, in effect, a ‘‘wet west/dry east’’ anomaly imposed on the realistic soil moisture pattern (that reflects the west-to-east climatological gradient). The impact of this anomaly, i.e., increasing soil moisture in the western half and decreasing it in the eastern half of the simulation domain, is most pronounced for the dry experiments and weakens nonlinearly with increasing domain-average initial soil moisture. In the dry regime, the impact is to enhance the total monthly precipitation in both the west and east. We examine the various terms in the atmospheric moisture budget to interpret these results. The changes in precipitation in the runs with a homogeneous compared to realistic initial soil moisture spatial pattern are consistent with enhanced evaporation in the western half of the model domain accompanied by enhanced west-to-east horizontal moisture transport that helps restore the initially depleted soil moisture in the east. In this manner, the zonal moisture flux acts toward re-establishing the initial climatological soil moisture pattern of the region, thus acting as a negative feedback mechanism. In addition, the soil moisture anomaly generally produces diminished meridional moisture transport into the simulation domain from the south through a decrease in the low-level meridional wind speed. This decrease in meridional flux acts in the same direction as the zonal flux change in the west, and in the opposite direction to the zonal flux change in the east. Since this change is most pronounced in the west, it therefore also contributes to the overall negative feedback of the atmospheric dynamics on the initial soil moisture. The persistence timescale of the impact of this particular soil moisture anomaly pattern on precipitation is on the order of 3 months in the dry regime. Sensitivity of the results to a change in convection scheme is also explored. INDEX TERMS: 1854 Hydrology: Precipitation (3354); 1866 Hydrology: Soil moisture; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; 3354 Meteorology and Atmospheric Dynamics: Precipitation (1854); KEYWORDS: land/atmosphere, precipitation, soil moisture

Challenges in applying the paradigm of welfare economics to climate change

Abstract This paper discusses the challenges inherent in developing benefit-cost analysis (BCAs) of climate change. Challenges are explored from three perspectives: meeting the foundational premises for conducting BCA within the framework of welfare economics, methodological considerations that affect the application of the tools and techniques of BCA, and practical limitations that arise out of resource constraints and the nature of the question, project, or policy being evaluated. Although economic analysts frequently face – and overcome – conceptual and practical complications in developing BCAs, climate change presents difficulties beyond those posed by more conventional environmental problems. Five characteristics of the climate system and associated impacts on human and natural systems are identified that pose particular challenges to BCA of climate change, including ubiquity of impacts, intangibility, non-marginal changes, long timeframes, and uncertainty. These characteristics interact with traditional economic challenges, such as valuing non-market impact, addressing non-marginal changes, accounting for low-probability but high-impact events, and the eternal issue of appropriately discounting the future. A mapping between the characteristics of climate change and traditional economic challenges highlights the difficulties analysts are likely to encounter in conducting BCA. Despite these challenges, the paper argues that the fundamental ability of economic analysis to evaluate alternatives and tradeoffs is vital to decision making. Climate-related decisions span a wide range in terms of their scope, complexity, and depth, and for many applications of economic analyses the issues associated with climate change are tractable. In other cases it may require improved economic techniques or taking steps to ensure uncertainty is more fully addressed. Augmenting economic analysis with distribution analysis or an account of physical effects, and exploring how economic benefit and cost estimates can be incorporated into broader decision making frameworks have also been suggested. The paper concludes that there are opportunities for BCA to play a key role in informing climate change decision-making.

The Interactions among Cyclone Dynamics, Vertical Thermodynamic Structure, and Cloud Radiative Forcing in the North Atlantic Summertime Storm Track

Abstract This study investigates the changes in the vertical thermodynamic structure of the troposphere associated with the passage of cyclones and the corresponding influence on cloud radiative forcing (CRF). The focus is the synoptic-scale evolution of lower-tropospheric sounding structure in the extratropical North Atlantic during July 1985–89. The type and amount of low-level cloud cover, which has a strong impact on total CRF in this region, is sensitive to these variations. Composite profiles at ocean weather stations L and C are constructed for soundings with low-level temperature inversions, soundings with surface-based inversions, and soundings without inversions, separately for conditions of large-scale subsidence and ascent. In addition, collocated European Centre for Medium-Range Weather Forecasts analyzed fields and Earth Radiation Budget Experiment CRF data are averaged for each composite sounding. These composites correspond to distinct dynamical regimes associated with the movement of cycl...