Kevin Lewis

November 22, 2017

Assessing the present and future probability of Hurricane Harvey’s rainfall
Kerry Emanuel
Proceedings of the National Academy of Sciences, forthcoming

We estimate, for current and future climates, the annual probability of areally averaged hurricane rain of Hurricane Harvey’s magnitude by downscaling large numbers of tropical cyclones from three climate reanalyses and six climate models. For the state of Texas, we estimate that the annual probability of 500 mm of area-integrated rainfall was about 1% in the period 1981–2000 and will increase to 18% over the period 2081–2100 under Intergovernmental Panel on Climate Change (IPCC) AR5 representative concentration pathway 8.5. If the frequency of such an event is increasing linearly between these two periods, then in 2017 the annual probability would be 6%, a sixfold increase since the late 20th century.

Recent very hot summers in northern hemispheric land areas measured by wet bulb globe temperature will be the norm within 20 years
Chao Li et al.
Earth's Future, forthcoming

Wet bulb Globe Temperature (WBGT) accounts for the effect of environmental temperature and humidity on thermal comfort, and can be directly related to the ability of the human body to dissipate excess metabolic heat and thus avoid heat stress. Using WBGT as a measure of environmental conditions conducive to heat stress, we show that anthropogenic influence has very substantially increased the likelihood of extreme high summer mean WBGT in northern hemispheric land areas relative to the climate that would have prevailed in the absence of anthropogenic forcing. We estimate that the likelihood of summer mean WGBT exceeding the observed historical record value has increased by a factor of at least 70 at regional scales due to anthropogenic influence on the climate. We further estimate that, in most northern hemispheric regions, these changes in the likelihood of extreme summer mean WBGT are roughly an order of magnitude larger than the corresponding changes in the likelihood of extreme hot summers as simply measured by surface air temperature. Projections of future summer mean WBGT under the RCP8.5 emissions scenario that are constrained by observations indicate that by 2030s at least 50% of the summers will have mean WBGT higher than the observed historical record value in all the analyzed regions, and that this frequency of occurrence will increase to 95% by mid-century.

Economic and environmental costs of replacing nuclear fission with solar and wind energy in Sweden
Sanghyun Hong, Staffan Qvist & Barry Brook
Energy Policy, January 2018, Pages 56–66

Nuclear power is facing an uncertain future in Sweden due to political directives that are seeking to phase out this energy source over coming decades. Here we examine the environmental and economic costs of hypothetical future renewable-energy-focused cases compared with the current nuclear and hydroelectricity-centred mix in Sweden. We show that if wind and photovoltaics replace entire nuclear power while maintaining the current level of dispatchable backup capacity including hydroelectric power and peak gas power, 154 GW of wind power will be required and will generate 427.1 TWh (compared with the actual demand of 143.7 TWh) to reliably meet demand each hour of the year. As a consequence, the annual spending on electricity systems will be five times higher than the status quo. Increasing dispatchable power, increasing transmission capacities to other countries, and generating electricity from combined heat and power plants even when there is no heat demand, will together reduce the required capacities of wind and solar photovoltaic by half, but it will double the greenhouse-gas emissions during the combustion process. In conclusion, our economic and greenhouse-gas emissions analyses demonstrate that replacing nuclear power with renewables will be neither economic nor environmentally-friendly with regards to the climate.

Impact of climate change on New York City’s coastal flood hazard: Increasing flood heights from the preindustrial to 2300 CE
Andra Garner et al.
Proceedings of the National Academy of Sciences, 7 November 2017, Pages 11861–11866

The flood hazard in New York City depends on both storm surges and rising sea levels. We combine modeled storm surges with probabilistic sea-level rise projections to assess future coastal inundation in New York City from the preindustrial era through 2300 CE. The storm surges are derived from large sets of synthetic tropical cyclones, downscaled from RCP8.5 simulations from three CMIP5 models. The sea-level rise projections account for potential partial collapse of the Antarctic ice sheet in assessing future coastal inundation. CMIP5 models indicate that there will be minimal change in storm-surge heights from 2010 to 2100 or 2300, because the predicted strengthening of the strongest storms will be compensated by storm tracks moving offshore at the latitude of New York City. However, projected sea-level rise causes overall flood heights associated with tropical cyclones in New York City in coming centuries to increase greatly compared with preindustrial or modern flood heights. For the various sea-level rise scenarios we consider, the 1-in-500-y flood event increases from 3.4 m above mean tidal level during 1970–2005 to 4.0–5.1 m above mean tidal level by 2080–2100 and ranges from 5.0–15.4 m above mean tidal level by 2280–2300. Further, we find that the return period of a 2.25-m flood has decreased from ∼500 y before 1800 to ∼25 y during 1970–2005 and further decreases to ∼5 y by 2030–2045 in 95% of our simulations. The 2.25-m flood height is permanently exceeded by 2280–2300 for scenarios that include Antarctica’s potential partial collapse.

First simulations of designing stratospheric sulfate aerosol geoengineering to meet multiple simultaneous climate objectives
Ben Kravitz et al.
Journal of Geophysical Research: Atmospheres, forthcoming

We describe the first simulations of stratospheric sulfate aerosol geoengineering using multiple injection locations to meet multiple simultaneous surface temperature objectives. Simulations were performed using CESM1(WACCM), a coupled atmosphere-ocean general circulation model with fully interactive stratospheric chemistry, dynamics (including an internally generated quasi-biennial oscillation), and a sophisticated treatment of sulfate aerosol formation, microphysical growth, and deposition. The objectives are defined as maintaining three temperature features at their 2020 levels against a background of the RCP8.5 scenario over the period 2020-2099. These objectives are met using a feedback mechanism in which the rate of sulfur dioxide injection at each of the four locations is adjusted independently every year of simulation. Even in the presence of uncertainties, nonlinearities, and variability, the objectives are met, predominantly by SO2 injection at 30° N and 30° S. By the last year of simulation, the feedback algorithm calls for a total injection rate of 51 Tg SO2 per year. The injections are not in the tropics, which results in a greater degree of linearity of the surface climate response with injection amount than has been found in many previous studies using injection at the equator. Because the objectives are defined in terms of annual mean temperature, the required geongineering results in “overcooling” during summer and “undercooling” during winter. The hydrological cycle is also suppressed as compared to the reference values corresponding to the year 2020. The demonstration we describe in this study is an important step toward understanding what geoengineering can do and what it cannot do.

Mandates and the Incentive for Environmental Innovation
Matthew Clancy & GianCarlo Moschini
American Journal of Agricultural Economics, forthcoming

Mandates, which establish minimum use quotas for certain goods, are becoming increasingly popular policy tools to promote renewable energy use. In addition to mitigating the pollution externality of conventional energy, clean energy mandates have the goal of promoting research and development (R&D) investments in renewable energy technology. But how well do mandates perform as innovation incentives? To address this question, we develop a partial equilibrium model to examine the R&D incentives induced by a mandate, and compare this policy to two benchmark situations: laissez faire and a carbon tax. Innovation is stochastic and the model permits an endogenous number of multiple innovators. We present both analytical results and conclusions based on numerical simulations. We find that the optimal mandate is larger than it would be without the prospect of innovation, that neglecting the outlook for innovation significantly reduces welfare, and that the optimal mandate is more sensitive to assumptions about the innovation process than an optimal carbon tax. Furthermore, we find that mandates create relatively strong incentives for R&D investment in low-quality innovations, but relatively weak incentives to invest in high-quality innovations. We also rank policies by expected welfare. An optimal carbon tax has higher expected welfare than an optimal mandate, and both have higher expected welfare than laissez faire. Moreover, in our endogenous innovation setting, a stronger result obtains: a simple carbon tax equal to the damage from pollution (unadjusted for the prospect of innovation) has higher expected welfare than an optimal mandate.

Nutritional and greenhouse gas impacts of removing animals from US agriculture
Robin White & Mary Beth Hall
Proceedings of the National Academy of Sciences, forthcoming

As a major contributor to agricultural greenhouse gas (GHG) emissions, it has been suggested that reducing animal agriculture or consumption of animal-derived foods may reduce GHGs and enhance food security. Because the total removal of animals provides the extreme boundary to potential mitigation options and requires the fewest assumptions to model, the yearly nutritional and GHG impacts of eliminating animals from US agriculture were quantified. Animal-derived foods currently provide energy (24% of total), protein (48%), essential fatty acids (23–100%), and essential amino acids (34–67%) available for human consumption in the United States. The US livestock industry employs 1.6 × 106 people and accounts for $31.8 billion in exports. Livestock recycle more than 43.2 × 109 kg of human-inedible food and fiber processing byproducts, converting them into human-edible food, pet food, industrial products, and 4 × 109 kg of N fertilizer. Although modeled plants-only agriculture produced 23% more food, it met fewer of the US population’s requirements for essential nutrients. When nutritional adequacy was evaluated by using least-cost diets produced from foods available, more nutrient deficiencies, a greater excess of energy, and a need to consume a greater amount of food solids were encountered in plants-only diets. In the simulated system with no animals, estimated agricultural GHG decreased (28%), but did not fully counterbalance the animal contribution of GHG (49% in this model). This assessment suggests that removing animals from US agriculture would reduce agricultural GHG emissions, but would also create a food supply incapable of supporting the US population’s nutritional requirements.

Outward migration may alter population dynamics and income inequality
Soheil Shayegh
Nature Climate Change, November 2017, Pages 828–832

Climate change impacts may drive affected populations to migrate. However, migration decisions in response to climate change could have broader effects on population dynamics in affected regions. Here, I model the effect of climate change on fertility rates, income inequality, and human capital accumulation in developing countries, focusing on the instrumental role of migration as a key adaptation mechanism. In particular, I investigate how climate-induced migration in developing countries will affect those who do not migrate. I find that holding all else constant, climate change raises the return on acquiring skills, because skilled individuals have greater migration opportunities than unskilled individuals. In response to this change in incentives, parents may choose to invest more in education and have fewer children. This may ultimately reduce local income inequality, partially offsetting some of the damages of climate change for low-income individuals who do not migrate.

The 2015 drought in Washington State: A harbinger of things to come?
Miriam Marlier et al.
Environmental Research Letters, November 2017

Washington State experienced widespread drought in 2015 and the largest burned area in the observational record, attributable in part to exceptionally low winter snow accumulation and high summer temperatures. We examine 2015 drought severity in the Cascade and Olympic mountains relative to the historical climatology (1950–present) and future climate projections (mid-21st century) for a mid-range global greenhouse gas emissions scenario. Although winter precipitation was near normal, the regional winter temperature anomaly was +2.1 °C (+2.0σ) in 2015, consistent with projections of a +2.3 °C (+2.2σ) temperature change and near normal precipitation in the future, relative to the climatology. April 1 snow water equivalent in 2015, −325 mm (−1.5σ), and the future, −252 mm (−1.1σ), were substantially lower than the climatology. Wildfire potential, as indicated by dead fuel moisture content, was higher in 2015 than mid-21st century mean projections. In contrast to most historical droughts, which have been driven by precipitation deficits, our results suggest that 2015 is a useful analog of typical conditions in the Pacific Northwest by the mid-21st century.

Increasing potential for intense tropical and subtropical thunderstorms under global warming
Martin Singh et al.
Proceedings of the National Academy of Sciences, 31 October 2017, Pages 11657–11662

Intense thunderstorms produce rapid cloud updrafts and may be associated with a range of destructive weather events. An important ingredient in measures of the potential for intense thunderstorms is the convective available potential energy (CAPE). Climate models project increases in summertime mean CAPE in the tropics and subtropics in response to global warming, but the physical mechanisms responsible for such increases and the implications for future thunderstorm activity remain uncertain. Here, we show that high percentiles of the CAPE distribution (CAPE extremes) also increase robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art climate models, implying strong increases in the frequency of occurrence of environments conducive to intense thunderstorms in future climate projections. The increase in CAPE extremes is consistent with a recently proposed theoretical model in which CAPE depends on the influence of convective entrainment on the tropospheric lapse rate, and we demonstrate the importance of this influence for simulated CAPE extremes using a climate model in which the convective entrainment rate is varied. We further show that the theoretical model is able to account for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in simulations and in observations. Our results provide a physical basis on which to understand projected future increases in intense thunderstorm potential, and they suggest that an important mechanism that contributes to such increases may be present in Earth’s atmosphere.

Temperature Effects on Productivity and Factor Reallocation: Evidence from a Half Million Chinese Manufacturing Plants
Peng Zhang et al.
Journal of Environmental Economics and Management, March 2018, Pages 1–17

This paper uses detailed production data from a half million Chinese manufacturing plants over 1998–2007 to estimate the effects of temperature on firm-level total factor productivity (TFP), factor inputs, and output. We detect an inverted U-shaped relationship between temperature and TFP and show that it primarily drives the temperature-output effect. Both labor- and capital- intensive firms exhibit sensitivity to high temperatures. By mid 21st century, if no additional adaptation were to occur, we project that climate change will reduce Chinese manufacturing output annually by 12%, equivalent to a loss of $39.5 billion in 2007 dollars. This implies substantial local and global economic consequences as the Chinese manufacturing sector produces 32% of national GDP and supplies 12% of global exports.

Habitat-based conservation strategies cannot compensate for climate-change-induced range loss
Johannes Wessely et al.
Nature Climate Change, November 2017, Pages 823–827

Anthropogenic habitat fragmentation represents a major obstacle to species shifting their range in response to climate change. Conservation measures to increase the (meta-)population capacity and permeability of landscapes may help but the effectiveness of such measures in a warming climate has rarely been evaluated. Here, we simulate range dynamics of 51 species from three taxonomic groups (vascular plants, butterflies and grasshoppers) in Central Europe as driven by twenty-first-century climate scenarios and analyse how three habitat-based conservation strategies (establishing corridors, improving the landscape matrix, and protected area management) modify species’ projected range size changes. These simulations suggest that the conservation strategies considered are unable to save species from regional extinction. For those persisting, they reduce the magnitude of range loss in lowland but not in alpine species. Protected area management and corridor establishment are more effective than matrix improvement. However, none of the conservation strategies evaluated could fully compensate the negative impact of climate change for vascular plants, butterflies or grasshoppers in central Europe.

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