Kevin Lewis

October 11, 2017

Redefining climate change inaction as temporal intergroup bias: Temporally adapted interventions for reducing prejudice may help elicit environmental protection
Rose Meleady & Richard Crisp
Journal of Environmental Psychology, November 2017, Pages 206-212


The consequences of the environmental decisions we make today will bear upon future generations of people. We argue that the framing of climate change is inherently intergroup in nature and suggest a reason for inaction on climate change is the perception of future generations as an outgroup. We test whether a technique adapted from the realm of intergroup relations may provide a novel approach to encouraging more sustainable environmental conduct. In Study 1 we found that participants who completed a simple social categorization technique designed to reduce (temporal) intergroup bias subsequently displayed a heightened preference for sustainable goods in a product choice task. Study 2 replicated these results with an alternative measure of pro-environmental intentions, and confirmed that the effect of the intervention on environmental outcomes was explained by changes in intergroup perception.

Extreme weather exposure and support for climate change adaptation
Aaron Ray et al.
Global Environmental Change, September 2017, Pages 104–113


Policy efforts to address climate change are increasingly focused on adaptation, understood as adjustments in human systems to moderate the harm, or exploit beneficial opportunities, related to actual or expected climate impacts. We examine individual-level determinants of support for climate adaptation policies, focusing on whether individuals’ exposure to extreme weather events is associated with their support for climate adaptation policies. Using novel public opinion data on support for a range of adaptation policies, coupled with high resolution geographic data on extreme weather events, we find that individuals experiencing recent extreme weather activity are more likely to support climate change adaptation policy in general, but that the relationship is modest, inconsistent across specific adaptation policies, and diminishes with time. The data thus suggest that experiencing more severe weather may not appreciably increase support for climate adaptation policies.

A Time Series Analysis of Associations between Daily Temperature and Crime Events in Philadelphia, Pennsylvania
Leah Schinasi & Ghassan Hamra
Journal of Urban Health, forthcoming


Urban crime may be an important but overlooked public health impact of rising ambient temperatures. We conducted a time series analysis of associations between temperature and crimes in Philadelphia, PA, for years 2006–2015. We obtained daily crime data from the Philadelphia Police Department, and hourly temperature and dew point data from the National Centers for Environmental Information. We calculated the mean daily heat index and daily deviations from each year’s seasonal mean heat index value. We used generalized additive models with a quasi-Poisson distribution, adjusted for day of the week, public holiday, and long-term trends and seasonality, to estimate relative rates (RR) and 95% confidence intervals. We found that the strongest associations were with violent crime and disorderly conduct. For example, relative to the median of the distribution of mean daily heat index values, the rate of violent crimes was 9% (95% CI 6–12%) higher when the mean daily heat index was at the 99th percentile of the distribution. There was a positive, linear relationship between deviations of the daily mean heat index from the seasonal mean and rates of violent crime and disorderly conduct, especially in cold months. Overall, these analyses suggest that disorderly conduct and violent crimes are highest when temperatures are comfortable, especially during cold months. This work provides important information regarding the temporal patterns of crime activity.

Flood Risk Belief Heterogeneity and Coastal Home Price Dynamics: Going Under Water?
Laura Bakkensen & Lint Barrage
NBER Working Paper, September 2017


How will climate risk beliefs affect coastal housing market dynamics? This paper provides both theoretical and empirical evidence: First, we build a dynamic housing market model with heterogeneity in home types, consumer preferences, and flood risk beliefs. The model incorporates a Bayesian learning mechanism allowing agents to update their beliefs depending on whether flood events occur. Second, to quantify these elements, we implement a door-to-door survey campaign in Rhode Island. The results confirm significant heterogeneity in flood risk beliefs, and that selection into coastal homes is driven by both lower risk perceptions and higher coastal amenity values. Third, we calibrate the model to simulate coastal home price trajectories given a future flood risk increase and policy reform across different belief scenarios. Accounting for heterogeneity increases the projected home price declines due to sea level rise by a factor of four, and increases market volatility by an order of magnitude. Studies assuming homogeneous rational expectations may thus substantially underestimate the home price implications of future climate risks. We conclude by highlighting potential implications for welfare and flood policy.

An Imperfect Storm: Fat-Tailed Tropical Cyclone Damages, Insurance, and Climate Policy
Marc Conte & David Kelly
Journal of Environmental Economics and Management, forthcoming


We perform two tests that estimate the mass of the upper tail of the distribution of aggregate US tropical cyclone damages. Both tests reject the hypothesis that the distribution of damages is thin tailed at the 95% confidence level, even after correcting for inflation and growth in population and per capita income. Our point estimates of the shape parameter of the damage distribution indicate that the distribution has finite mean, but infinite variance. In the second part of the paper, we develop a microfoundations model of insurance and storm size that generates a fat tail in aggregate tropical cyclone damages. The distribution of the number of properties within a random geographical area that lies in the path of a tropical cyclone is shown to drive fat tailed storm damages, and we confirm that the distribution of coastal city population is fat tailed in the US. We show empirically and theoretically that other random variation, such as the distribution of storm strength and the distribution of damages across individual properties, does not generate a fat tail. We consider policy options such as climate change abatement, policies which encourage adaptation, reducing subsidies for coastal development, and disaster relief policies, which distort insurance markets. Such policies can reduce the thickness of the tail, but do not affect the shape parameter or the existence of the fat tail.

Another avenue of action: An examination of climate change countermovement industries use of PAC donations and their relationship to Congressional voting over time
Kerry Ard, Nick Garcia & Paige Kelly
Environmental Politics, November/December 2017, Pages 1107-1131


The political mobilization of American business elites in the 1970s and 1980s has been well studied by political scientists. Environmental sociologists have explored how industries in this elite countermovement have organized to prevent environmental legislation. The literature often focuses on the efforts of this movement to shape public opinion on climate change. However, political scientists argue business elites are running several parallel strategies simultaneously in order to protect their interests. FEC data are utilized in multilevel logit models to examine how donations from industrial Political Action Committees (PACs) relate to Congressional representative’s environmental voting behavior over a 20-year period. Industries associated with the environmental countermovement have increasingly used PAC donations over time, and every additional $10,000 a representative received from countermovement industries significantly decreased odds of their taking the pro-environmental stance even when controlling for representatives’ demographics, districts, Congressional polarization and time-period.

Public willingness to pay for a US carbon tax and preferences for spending the revenue
Matthew Kotchen, Zachary Turk & Anthony Leiserowitz
Environmental Research Letters, September 2017


We provide evidence from a nationally representative survey on Americans' willingness to pay (WTP) for a carbon tax, and public preferences for how potential carbon-tax revenue should be spent. The average WTP for a tax on fossil fuels that increases household energy bills is US$177 per year. This translates into an average WTP of 14% more on average for households across the United States, where energy costs differ significantly across states. Regarding the tax revenues, Americans are most in support of using the money to invest in clean energy and infrastructure. There is relatively less support for reducing income or payroll taxes, returning dividends to households, and other expenditure categories. Finally, Americans support using the tax revenues to assist displaced workers in the coal industry enough to compensate each miner nearly US$146 000 upon passage of a carbon tax.

Increased costs to US pavement infrastructure from future temperature rise
Shane Underwood et al.
Nature Climate Change, October 2017, Pages 704–707


Roadway design aims to maximize functionality, safety, and longevity. The materials used for construction, however, are often selected on the assumption of a stationary climate. Anthropogenic climate change may therefore result in rapid infrastructure failure and, consequently, increased maintenance costs, particularly for paved roads where temperature is a key determinant for material selection. Here, we examine the economic costs of projected temperature changes on asphalt roads across the contiguous United States using an ensemble of 19 global climate models forced with RCP 4.5 and 8.5 scenarios. Over the past 20 years, stationary assumptions have resulted in incorrect material selection for 35% of 799 observed locations. With warming temperatures, maintaining the standard practice for material selection is estimated to add approximately US$13.6, US$19.0 and US$21.8 billion to pavement costs by 2010, 2040 and 2070 under RCP4.5, respectively, increasing to US$14.5, US$26.3 and US$35.8 for RCP8.5. These costs will disproportionately affect local municipalities that have fewer resources to mitigate impacts. Failing to update engineering standards of practice in light of climate change therefore significantly threatens pavement infrastructure in the United States.

Emissions embodied in global trade have plateaued due to structural changes in China
Chen Pan et al.
Earth's Future, forthcoming


In the 2000s, the rapid growth of CO2 emitted in the production of exports from developing to developed countries, in which China accounted for the dominant share, led to concerns that climate polices had been undermined by international trade. Arguments on ‘carbon leakage’ and ‘competitiveness’ – which led to the refusal of the United States to ratify the Kyoto Protocol – put pressure on developing countries, especially China, to limit their emissions with Border Carbon Adjustments used as one threat. After strong growth in the early 2000s, emissions exported from developing to developed countries plateaued and could have even decreased since 2007. These changes were mainly due to China: In 2002–2007, China’s exported emissions grew by 827 MtCO2, amounting to almost all the 892 MtCO2 total increase in emissions exported from developing to developed countries, while in 2007–2012, emissions exported from China decreased by 229 MtCO2, contributing to the total decrease of 172 MtCO2 exported from developing to developed countries. We apply Structural Decomposition Analysis to find that, in addition to the diminishing effects of the global financial crisis, the slowdown and eventual plateau was largely explained by several potentially permanent changes in China: Decline in export volume growth, improvements in CO2 intensity, and changes in production structure and the mix of exported products. We argue that growth in China’s exported emissions will not return to the high levels during the 2000s, therefore the arguments for climate polices focused on embodied emissions such as Border Carbon Adjustments are now weakened.

Addressing concerns about climate policies: The possibilities and perils of responsive accommodation
Graham Bullock & Alexander Theodoridis
Environmental Politics, November/December 2017, Pages 1079-1106


Responsive accommodation is a political strategy that addresses concerns about a policy proposal by incorporating amendments that address those concerns. This approach can broaden the policy’s appeal, but is strategically risky, as it can alienate the policy’s base of support. We examine this strategy and its application in the politics of climate change. Using a novel survey experiment, relative public support is evaluated for two amendments to a carbon tax proposal – revenue neutrality assurances and a carbon tariff – designed to ease concerns about taxes and global competitiveness. Analysis shows that support for a carbon tax increases when coupled with a carbon tariff, but decreases among some of the policy’s supporters when described as revenue-neutral. These results suggest that policymakers using a responsive accommodation strategy must carefully weigh its possible risks and rewards in their particular context.

Change in the magnitude and mechanisms of global temperature variability with warming
Patrick Brown et al.
Nature Climate Change, October 2017, Pages 743–748


Natural unforced variability in global mean surface air temperature (GMST) can mask or exaggerate human-caused global warming, and thus a complete understanding of this variability is highly desirable. Significant progress has been made in elucidating the magnitude and physical origins of present-day unforced GMST variability, but it has remained unclear how such variability may change as the climate warms. Here we present modelling evidence that indicates that the magnitude of low-frequency GMST variability is likely to decline in a warmer climate and that its generating mechanisms may be fundamentally altered. In particular, a warmer climate results in lower albedo at high latitudes, which yields a weaker albedo feedback on unforced GMST variability. These results imply that unforced GMST variability is dependent on the background climatological conditions, and thus climate model control simulations run under perpetual pre-industrial conditions may have only limited relevance for understanding the unforced GMST variability of the future.

Steering the Climate System: Using Inertia to Lower the Cost of Policy
Derek Lemoine & Ivan Rudik
American Economic Review, October 2017, Pages 2947-2957


Common views hold that the efficient way to limit warming to a chosen level is to price carbon emissions at a rate that increases exponentially. We show that this Hotelling tax on carbon emissions is actually inefficient. The least-cost policy path takes advantage of the climate system's inertia to delay reducing emissions and allow greater cumulative emissions. The efficient carbon tax follows an inverse-U-shaped path and grows more slowly than the Hotelling tax. Economic models that assume exponentially increasing carbon taxes are overestimating the cost of limiting warming, overestimating the efficient near-term carbon tax, and overvaluing technologies that mature sooner.

Attributing extreme fire risk in Western Canada to human emissions
Megan Kirchmeier-Young et al.
Climatic Change, September 2017, Pages 365–379


Canada is expected to see an increase in fire risk under future climate projections. Large fires, such as that near Fort McMurray, Alberta in 2016, can be devastating to the communities affected. Understanding the role of human emissions in the occurrence of such extreme fire events can lend insight into how these events might change in the future. An event attribution framework is used to quantify the influence of anthropogenic forcings on extreme fire risk in the current climate of a western Canada region. Fourteen metrics from the Canadian Forest Fire Danger Rating System are used to define the extreme fire seasons. For the majority of these metrics and during the current decade, the combined effect of anthropogenic and natural forcing is estimated to have made extreme fire risk events in the region 1.5 to 6 times as likely compared to a climate that would have been with natural forcings alone.

Potential climate change impacts on fire intensity and key wildfire suppression thresholds in Canada
B.M. Wotton, M.D. Flannigan & G.A. Marshall
Environmental Research Letters, September 2017


Much research has been carried out on the potential impacts of climate change on forest fire activity in the boreal forest. Indeed, there is a general consensus that, while change will vary regionally across the vast extent of the boreal, in general the fire environment will become more conducive to fire. Land management agencies must consider ways to adapt to these new conditions. This paper examines the impact of that changed fire environment on overall wildfire suppression capability. We use multiple General Circulation Models and carbon emission pathways to generate future fire environment scenarios for Canada's forested region. We then use these scenarios with the Canadian Forest Fire Behaviour Prediction System and spatial coverages of the current forest fuel composition across the landscape to examine potential variation in key fire behaviour outputs that influence whether fire management resources can effectively suppress fire. Specifically, we evaluate how the potential for crown fire occurrence and active growth of fires changes with the changing climate. We also examine future fire behaviour through the lens of operational fire intensity thresholds used to guide decisions about resources effectiveness. Results indicate that the proportion of days in fire seasons with the potential for unmanageable fire will increase across Canada's forest, more than doubling in some regions in northern and eastern boreal forest.

Annual and seasonal tornado trends in the contiguous United States and its regions
Todd Moore
International Journal of Climatology, forthcoming


Previous studies provide evidence of possible changes to the climatology of tornadoes in the United States. These include a decrease in the number of tornado days per year, but an increase in the number of days per year with a large number of tornadoes; an increase in the mean number of tornadoes per tornado day; a spatial shift in tornado activity, generally towards the Southeast United States. Most of these studies, however, tend to examine trends at the annual (or spring) and contiguous United States scales. Using tornado data over the period 1954–2016, this study analyses various tornado metrics to determine whether trends are consistent throughout the year and across the United States. Trends are assessed with the Mann–Kendall test and their slopes with the Theil–Sen estimator. The annual analyses indicate that the number of tornadoes per year declined in the West, North Great Plains, South Great Plains, and Midwest regions, but increased in the Southeast. The decreasing/increasing tendencies in the South Great Plains/Southeast led to a reversal of the most active region – the South Great Plains had the greatest median tornado frequency early in the study period whereas the Southeast had the greatest in the middle and late periods. Annual analyses also indicate that the previously reported decline in the number of tornado days per year and the increase in the mean number of tornadoes per tornado day per year are generally present across the United States. Seasonal analyses suggest that the proportion of tornadoes occurring in the contiguous United States in summer is decreasing whereas the proportion occurring in fall is increasing. This is especially apparent in the Southeast.

Was it worthwhile? Where have the benefits of rooftop solar photovoltaic generation exceeded the cost?
Parth Vaishnav, Nathaniel Horner & Inês Azevedo
Environmental Research Letters, September 2017


We estimate the lifetime magnitude and distribution of the private and public benefits and costs of currently installed distributed solar PV systems in the United States. Using data for recently-installed systems, we estimate the balance of benefits and costs associated with installing a non-utility solar PV system today. We also study the geographical distribution of the various subsidies that are made available to owners of rooftop solar PV systems, and compare it to distributions of population and income. We find that, after accounting for federal subsidies and local rebates and assuming a discount rate of 7%, the private benefits of new installations will exceed private costs only in seven of the 19 states for which we have data and only if customers can sell excess power to the electric grid at the retail price. These states are characterized by abundant sunshine (California, Texas and Nevada) or by high electricity prices (New York). Public benefits from reduced air pollution and climate change impact exceed the costs of the various subsidies offered system owners for less than 10% of the systems installed, even assuming a 2% discount rate. Subsidies flowed disproportionately to counties with higher median incomes in 2006. In 2014, the distribution of subsidies was closer to that of population income, but subsidies still flowed disproportionately to the better-off. The total, upfront, subsidy per kilowatt of installed capacity has fallen from $5200 in 2006 to $1400 in 2014, but the absolute magnitude of subsidy has soared as installed capacity has grown explosively. We see considerable differences in the balance of costs and benefits even within states, indicating that local factors such as system price and solar resource are important, and that policies (e.g. net metering) could be made more efficient by taking local conditions into account.

Changes in regional heatwave characteristics as a function of increasing global temperature
S.E. Perkins-Kirkpatrick & P.B. Gibson
Scientific Reports, September 2017


The Paris Agreement calls for global warming to be limited to 1.5–2 °C. For the first time, this study investigates how different regional heatwave characteristics (intensity, frequency and duration) are projected to change relative to increasing global warming thresholds. Increases in heatwave days between 4–34 extra days per season are projected per °C of global warming. Some tropical regions could experience up to 120 extra heatwave days/season if 5 °C is reached. Increases in heatwave intensity are generally 0.5–1.5 °C above a given global warming threshold, however are higher over the Mediterranean and Central Asian regions. Between warming thresholds of 1.5 °C and 2.5 °C, the return intervals of intense heatwaves reduce by 2–3 fold. Heatwave duration is projected to increase by 2–10 days/°C, with larger changes over lower latitudes. Analysis of two climate model ensembles indicate that variation in the rate of heatwave changes is dependent on physical differences between different climate models, however internal climate variability bears considerable influence on the expected range of regional heatwave changes per warming threshold. The results of this study reiterate the potential for disastrous consequences associated with regional heatwaves if global mean warming is not limited to 2 degrees.

Ghost reefs: Nautical charts document large spatial scale of coral reef loss over 240 years
Loren McClenachan et al.
Science Advances, September 2017


Massive declines in population abundances of marine animals have been documented over century-long time scales. However, analogous loss of spatial extent of habitat-forming organisms is less well known because georeferenced data are rare over long time scales, particularly in subtidal, tropical marine regions. We use high-resolution historical nautical charts to quantify changes to benthic structure over 240 years in the Florida Keys, finding an overall loss of 52% (SE, 6.4%) of the area of the seafloor occupied by corals. We find a strong spatial dimension to this decline; the spatial extent of coral in Florida Bay and nearshore declined by 87.5% (SE, 7.2%) and 68.8% (SE, 7.5%), respectively, whereas that of offshore areas of coral remained largely intact. These estimates add to finer-scale loss in live coral cover exceeding 90% in some locations in recent decades. The near-complete elimination of the spatial coverage of nearshore coral represents an underappreciated spatial component of the shifting baseline syndrome, with important lessons for other species and ecosystems. That is, modern surveys are typically designed to assess change only within the species’ known, extant range. For species ranging from corals to sea turtles, this approach may overlook spatial loss over longer time frames, resulting in both overly optimistic views of their current conservation status and underestimates of their restoration potential.

Tropical forests are a net carbon source based on aboveground measurements of gain and loss
Alessandro Baccini et al.
Science, forthcoming


The carbon balance of tropical ecosystems remains uncertain, with top-down atmospheric studies suggesting an overall sink and bottom-up ecological approaches indicating a modest net source. Here we use 12 years (2003–2014) of MODIS pantropical satellite data to quantify net annual changes in the aboveground carbon density of tropical woody live vegetation, providing direct, measurement-based evidence that the world’s tropical forests are a net carbon source of 425.2 ± 92.0 Tg C yr–1. This net release of carbon consists of losses of 861.7 ± 80.2 Tg C yr–1 and gains of 436.5 ± 31.0 Tg C yr–1. Gains result from forest growth; losses result from deforestation and from reductions in carbon density within standing forests (degradation/disturbance), with the latter accounting for 68.9% of overall losses.

Causal knowledge promotes behavioral self-regulation: An example using climate change dynamics
David Sewell et al.
PLoS ONE, September 2017


Adopting successful climate change mitigation policies requires the public to choose how to balance the sometimes competing goals of managing CO2 emissions and achieving economic growth. It follows that collective action on climate change depends on members of the public to be knowledgeable of the causes and economic ramifications of climate change. The existing literature, however, shows that people often struggle to correctly reason about the fundamental accumulation dynamics that drive climate change. Previous research has focused on using analogy to improve people’s reasoning about accumulation, which has been met with some success. However, these existing studies have neglected the role economic factors might play in shaping people’s decisions in relation to climate change. Here, we introduce a novel iterated decision task in which people attempt to achieve a specific economic goal by interacting with a causal dynamic system in which human economic activities, CO2 emissions, and warming are all causally interrelated. We show that when the causal links between these factors are highlighted, people’s ability to achieve the economic goal of the task is enhanced in a way that approaches optimal responding, and avoids dangerous levels of warming.

Well below 2 °C: Mitigation strategies for avoiding dangerous to catastrophic climate changes
Yangyang Xu & Veerabhadran Ramanathan
Proceedings of the National Academy of Sciences, 26 September 2017, Pages 10315–10323


The historic Paris Agreement calls for limiting global temperature rise to “well below 2 °C.” Because of uncertainties in emission scenarios, climate, and carbon cycle feedback, we interpret the Paris Agreement in terms of three climate risk categories and bring in considerations of low-probability (5%) high-impact (LPHI) warming in addition to the central (∼50% probability) value. The current risk category of dangerous warming is extended to more categories, which are defined by us here as follows: >1.5 °C as dangerous; >3 °C as catastrophic; and >5 °C as unknown, implying beyond catastrophic, including existential threats. With unchecked emissions, the central warming can reach the dangerous level within three decades, with the LPHI warming becoming catastrophic by 2050. We outline a three-lever strategy to limit the central warming below the dangerous level and the LPHI below the catastrophic level, both in the near term (<2050) and in the long term (2100): the carbon neutral (CN) lever to achieve zero net emissions of CO2, the super pollutant (SP) lever to mitigate short-lived climate pollutants, and the carbon extraction and sequestration (CES) lever to thin the atmospheric CO2 blanket. Pulling on both CN and SP levers and bending the emissions curve by 2020 can keep the central warming below dangerous levels. To limit the LPHI warming below dangerous levels, the CES lever must be pulled as well to extract as much as 1 trillion tons of CO2 before 2100 to both limit the preindustrial to 2100 cumulative net CO2 emissions to 2.2 trillion tons and bend the warming curve to a cooling trend.

North–south polarization of European electricity consumption under future warming
Leonie Wenz, Anders Levermann & Maximilian Auffhammer
Proceedings of the National Academy of Sciences, 19 September 2017, Pages E7910–E7918


There is growing empirical evidence that anthropogenic climate change will substantially affect the electric sector. Impacts will stem both from the supply side — through the mitigation of greenhouse gases — and from the demand side — through adaptive responses to a changing environment. Here we provide evidence of a polarization of both peak load and overall electricity consumption under future warming for the world’s third-largest electricity market—the 35 countries of Europe. We statistically estimate country-level dose–response functions between daily peak/total electricity load and ambient temperature for the period 2006–2012. After removing the impact of nontemperature confounders and normalizing the residual load data for each country, we estimate a common dose–response function, which we use to compute national electricity loads for temperatures that lie outside each country’s currently observed temperature range. To this end, we impose end-of-century climate on today’s European economies following three different greenhouse-gas concentration trajectories, ranging from ambitious climate-change mitigation — in line with the Paris agreement — to unabated climate change. We find significant increases in average daily peak load and overall electricity consumption in southern and western Europe (∼3 to ∼7% for Portugal and Spain) and significant decreases in northern Europe (∼−6 to ∼−2% for Sweden and Norway). While the projected effect on European total consumption is nearly zero, the significant polarization and seasonal shifts in peak demand and consumption have important ramifications for the location of costly peak-generating capacity, transmission infrastructure, and the design of energy-efficiency policy and storage capacity.

Leakage risks of geologic CO2 storage and the impacts on the global energy system and climate change mitigation
Hang Deng et al.
Climatic Change, September 2017, Pages 151–163


This study investigated how subsurface and atmospheric leakage from geologic CO2 storage reservoirs could impact the deployment of Carbon Capture and Storage (CCS) in the global energy system. The Leakage Risk Monetization Model was used to estimate the costs of leakage for representative CO2 injection scenarios, and these costs were incorporated into the Global Change Assessment Model. Worst-case scenarios of CO2 leakage risk, which assume that all leakage pathway permeabilities are extremely high, were simulated. Even with this extreme assumption, the associated costs of monitoring, treatment, containment, and remediation resulted in minor shifts in the global energy system. For example, the reduction in CCS deployment in the electricity sector was 3% for the “high” leakage scenario, with replacement coming from fossil fuel and biomass without CCS, nuclear power, and renewable energy. In other words, the impact on CCS deployment under a realistic leakage scenario is likely to be negligible. We also quantified how the resulting shifts will impact atmospheric CO2 concentrations. Under a carbon tax that achieves an atmospheric CO2 concentration of 480 ppm in 2100, technology shifts due to leakage costs would increase this concentration by less than 5 ppm. It is important to emphasize that this increase does not result from leaked CO2 that reaches the land surface, which is minimal due to secondary trapping in geologic strata above the storage reservoir. The overall conclusion is that leakage risks and associated costs will likely not interfere with the effectiveness of policies for climate change mitigation.

Increasing atmospheric humidity and CO2 concentration alleviate forest mortality risk
Yanlan Liu et al.
Proceedings of the National Academy of Sciences, 12 September 2017, Pages 9918–9923


Climate-induced forest mortality is being increasingly observed throughout the globe. Alarmingly, it is expected to exacerbate under climate change due to shifting precipitation patterns and rising air temperature. However, the impact of concomitant changes in atmospheric humidity and CO2 concentration through their influence on stomatal kinetics remains a subject of debate and inquiry. By using a dynamic soil–plant–atmosphere model, mortality risks associated with hydraulic failure and stomatal closure for 13 temperate and tropical forest biomes across the globe are analyzed. The mortality risk is evaluated in response to both individual and combined changes in precipitation amounts and their seasonal distribution, mean air temperature, specific humidity, and atmospheric CO2 concentration. Model results show that the risk is predicted to significantly increase due to changes in precipitation and air temperature regime for the period 2050–2069. However, this increase may largely get alleviated by concurrent increases in atmospheric specific humidity and CO2 concentration. The increase in mortality risk is expected to be higher for needleleaf forests than for broadleaf forests, as a result of disparity in hydraulic traits. These findings will facilitate decisions about intervention and management of different forest types under changing climate.

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