Not for attribution

Kevin Lewis

August 30, 2017

A Survey of Global Impacts of Climate Change: Replication, Survey Methods, and a Statistical Analysis
William Nordhaus & Andrew Moffat
NBER Working Paper, August 2017

The present study has two objectives. The first is a review of studies that estimate the global economic impacts of climate change using a systematic research synthesis (SRS). In this review, we attempt to replicate the impact estimates provided by Tol (2009, 2014) and find a large number of errors and estimates that could not be replicated. The study provides revised estimates for a total of 36 usable estimates from 27 studies. A second part of the study performs a statistical analysis. While the different specifications provide alternative estimates of the damage function, there were no large discrepancies among specifications. The preferred regression is the median, quadratic, weighted regression. The data here omit several important potential damages, which we estimate to add 25% to the quantified damages. With this addition, the estimated impact is -2.04 (± 2.21) % of income at 3 °C warming and -8.06 (± 2.43) % of income at 6 °C warming. We also considered the likelihood of thresholds or sharp convexities in the damage function and found no evidence from the damage estimates of a sharp discontinuity or high convexity.

The Trade-off Between Income Inequality and Carbon Dioxide Emissions
Nicole Grunewald et al.
Ecological Economics, December 2017, Pages 249-256

We investigate the theoretically ambiguous link between income inequality and per capita carbon dioxide emissions using a panel data set that is substantially larger (in both regional and temporal coverage) than those used in the existing literature. Using an arguably superior group fixed effects estimator, we find that the relationship between income inequality and per capita emissions depends on the level of income. We show that for low and middle-income economies, higher income inequality is associated with lower carbon emissions while in upper middle-income and high-income economies, higher income inequality increases per capita emissions. The result is robust to the inclusion of plausible transmission variables.

Examining the Association Between Temperature and Emergency Room Visits from Mental Health-Related Outcomes in California
Rupa Basu et al.
American Journal of Epidemiology, forthcoming

Temperature and morbidity has been explored previously. However, the association between temperature and mental health-related outcomes, including violence and self-harm, remains relatively unexamined. We obtained daily counts of mental health-related emergency room visits involving injuries with external cause from the California Office of Statewide Health Planning and Development from 16 California climate zones from 2005 to 2013, and combined them with data on mean apparent temperature, a combination of temperature and humidity. Using Poisson regression models, we estimated climate zone-level associations, then used random-effects meta-analyses to produce overall estimates. Analyses were stratified by season (warm: May-October; cold: November-April), race/ethnicity, and age. A 10-degree Fahrenheit increase in same-day mean apparent temperature was associated with a 4.8% (95% confidence interval, 3.6-6.0%), 5.8% (4.5-7.1%), and 7.9% (7.3-8.4%) increase in visits for mental health disorders, self-injury/suicide, and intentional injury/homicide, respectively, during the warm season. High temperatures during the cold season were also positively associated with these outcomes. Variations were observed by race/ethnicity, age group, and sex, with Hispanics, Whites, 6-18 year olds, and females at greatest risk for most outcomes. Increasing mean apparent temperature was found to have acute associations with mental health outcomes and intentional injuries, and warrants further studies in other locations.

Humid heat waves at different warming levels
Simone Russo, Jana Sillmann & Andreas Sterl
Scientific Reports, August 2017

The co-occurrence of consecutive hot and humid days during a heat wave can strongly affect human health. Here, we quantify humid heat wave hazard in the recent past and at different levels of global warming. We find that the magnitude and apparent temperature peak of heat waves, such as the ones observed in Chicago in 1995 and China in 2003, have been strongly amplified by humidity. Climate model projections suggest that the percentage of area where heat wave magnitude and peak are amplified by humidity increases with increasing warming levels. Considering the effect of humidity at 1.5° and 2° global warming, highly populated regions, such as the Eastern US and China, could experience heat waves with magnitude greater than the one in Russia in 2010 (the most severe of the present era). The apparent temperature peak during such humid-heat waves can be greater than 55 °C. According to the US Weather Service, at this temperature humans are very likely to suffer from heat strokes. Humid-heat waves with these conditions were never exceeded in the present climate, but are expected to occur every other year at 4° global warming. This calls for respective adaptation measures in some key regions of the world along with international climate change mitigation efforts.

The influence of learning about carbon dioxide removal (CDR) on support for mitigation policies
Victoria Campbell-Arvai et al.
Climatic Change, August 2017, Pages 321–336

A wide range of carbon dioxide removal (CDR) strategies has been proposed to address climate change. As most CDR strategies are unfamiliar to the public, it is unknown how increased media and policy attention on CDR might affect public sentiment about climate change. On the one hand, CDR poses a potential moral hazard: if people perceive that CDR solves climate change, they may be less likely to support efforts to reduce carbon emissions. On the other hand, the need for CDR may increase the perceived severity of climate change and, thus, increase support for other types of mitigation. Using an online survey of US adults (N = 984), we tested these competing hypotheses by exposing participants to information about different forms of CDR. We find that learning about certain CDR strategies indirectly reduces support for mitigation policies by reducing the perceived threat of climate change. This was found to be true for participants who read about CDR in general (without mention of specific strategies), bioenergy with carbon capture and storage, or direct air capture. Furthermore, this risk compensation pattern was more pronounced among political conservatives than liberals — although in some cases, was partially offset by positive direct effects. Learning about reforestation, by contrast, had no indirect effects on mitigation support through perceived threat but was found to directly increase support among conservatives. The results suggest caution is warranted when promoting technological fixes to climate change, like CDR, as some forms may further dampen support for climate change action among the unengaged.

Assessing ExxonMobil's climate change communications (1977–2014)
Geoffrey Supran & Naomi Oreskes
Environmental Research Letters, August 2017

This paper assesses whether ExxonMobil Corporation has in the past misled the general public about climate change. We present an empirical document-by-document textual content analysis and comparison of 187 climate change communications from ExxonMobil, including peer-reviewed and non-peer-reviewed publications, internal company documents, and paid, editorial-style advertisements ('advertorials') in The New York Times. We examine whether these communications sent consistent messages about the state of climate science and its implications — specifically, we compare their positions on climate change as real, human-caused, serious, and solvable. In all four cases, we find that as documents become more publicly accessible, they increasingly communicate doubt. This discrepancy is most pronounced between advertorials and all other documents. For example, accounting for expressions of reasonable doubt, 83% of peer-reviewed papers and 80% of internal documents acknowledge that climate change is real and human-caused, yet only 12% of advertorials do so, with 81% instead expressing doubt. We conclude that ExxonMobil contributed to advancing climate science — by way of its scientists' academic publications — but promoted doubt about it in advertorials. Given this discrepancy, we conclude that ExxonMobil misled the public. Our content analysis also examines ExxonMobil's discussion of the risks of stranded fossil fuel assets. We find the topic discussed and sometimes quantified in 24 documents of various types, but absent from advertorials. Finally, based on the available documents, we outline ExxonMobil's strategic approach to climate change research and communication, which helps to contextualize our findings.

How Much Will the Sea Level Rise? Outcome Selection and Subjective Probability in Climate Change Predictions
Marie Juanchich & Miroslav Sirota
Journal of Experimental Psychology: Applied, forthcoming

We tested whether people focus on extreme outcomes to predict climate change and assessed the gap between the frequency of the predicted outcome and its perceived probability while controlling for climate change beliefs. We also tested 2 cost-effective interventions to reduce the preference for extreme outcomes and the frequency–probability gap by manipulating the probabilistic format: numerical or dual-verbal-numerical. In 4 experiments, participants read a scenario featuring a distribution of sea level rises, selected a sea rise to complete a prediction (e.g., “It is ‘unlikely’ that the sea level will rise . . . inches”) and judged the likelihood of this sea rise occurring. Results showed that people have a preference for predicting extreme climate change outcomes in verbal predictions (59% in Experiments 1–4) and that this preference was not predicted by climate change beliefs. Results also showed an important gap between the predicted outcome frequency and participants’ perception of the probability that it would occur. The dual-format reduced the preference for extreme outcomes for low and medium probability predictions but not for high ones, and none of the formats consistently reduced the frequency–probability gap.

Temperature increase reduces global yields of major crops in four independent estimates
Chuang Zhao et al.
Proceedings of the National Academy of Sciences, 29 August 2017, Pages 9326–9331

Wheat, rice, maize, and soybean provide two-thirds of human caloric intake. Assessing the impact of global temperature increase on production of these crops is therefore critical to maintaining global food supply, but different studies have yielded different results. Here, we investigated the impacts of temperature on yields of the four crops by compiling extensive published results from four analytical methods: global grid-based and local point-based models, statistical regressions, and field-warming experiments. Results from the different methods consistently showed negative temperature impacts on crop yield at the global scale, generally underpinned by similar impacts at country and site scales. Without CO2 fertilization, effective adaptation, and genetic improvement, each degree-Celsius increase in global mean temperature would, on average, reduce global yields of wheat by 6.0%, rice by 3.2%, maize by 7.4%, and soybean by 3.1%. Results are highly heterogeneous across crops and geographical areas, with some positive impact estimates. Multimethod analyses improved the confidence in assessments of future climate impacts on global major crops and suggest crop- and region-specific adaptation strategies to ensure food security for an increasing world population.

Consequences of a Carbon Tax on Household Electricity Use and Cost, Carbon Emissions, and Economics of Household Solar and Wind
Ahmad Ghaith & Francis Epplin
Energy Economics, forthcoming

The study was conducted to determine the consequences of a carbon tax, equal to an estimated social cost of carbon of $37.2/Mg, on household electricity cost, and to determine if a carbon tax would be sufficient to incentivize households to install either a grid-tied solar or wind system. U.S. Department of Energy hourly residential profiles for five locations, 20 years of hourly weather data, prevailing electricity pricing rate schedules, and purchase prices and solar panel and wind turbine power output response functions, were used to address the objectives. Two commercially available household solar panels (4 kW, 12 kW), two wind turbines (6 kW, 12 kW), and two price rate structures (traditional meter, smart meter) were considered. Averaged across the five households, the carbon tax is expected to reduce annual consumption by 4.4% (552 kWh/year) for traditional meter households and by 4.9% (611 kWh/year) for households charged smart meter rates. The carbon tax increases electricity cost by 19% ($202/year). For a household cost of $202/year the carbon tax is expected to reduce social costs by $11. Annual carbon tax collections of $234/household are expected. Adding the carbon tax was found to be insufficient to incentivize households to install either a solar panel or wind turbine system. Installation of a 4 kW solar system would increase the annual cost by $1546 (247%) and decrease CO2 emissions by 38% (2526 kg) valued at $94/household. The consequence of a carbon tax would depend largely on how the proceeds of the tax are used.

Less than 2 °C warming by 2100 unlikely
Adrian Raftery et al.
Nature Climate Change, forthcoming

The recently published Intergovernmental Panel on Climate Change (IPCC) projections to 2100 give likely ranges of global temperature increase in four scenarios for population, economic growth and carbon use. However, these projections are not based on a fully statistical approach. Here we use a country-specific version of Kaya’s identity to develop a statistically based probabilistic forecast of CO2 emissions and temperature change to 2100. Using data for 1960–2010, including the UN’s probabilistic population projections for all countries, we develop a joint Bayesian hierarchical model for Gross Domestic Product (GDP) per capita and carbon intensity. We find that the 90% interval for cumulative CO2 emissions includes the IPCC’s two middle scenarios but not the extreme ones. The likely range of global temperature increase is 2.0–4.9 °C, with median 3.2 °C and a 5% (1%) chance that it will be less than 2 °C (1.5 °C). Population growth is not a major contributing factor. Our model is not a ‘business as usual’ scenario, but rather is based on data which already show the effect of emission mitigation policies. Achieving the goal of less than 1.5 °C warming will require carbon intensity to decline much faster than in the recent past.

Committed warming inferred from observations
Thorsten Mauritsen & Robert Pincus
Nature Climate Change, forthcoming

Due to the lifetime of CO2, the thermal inertia of the oceans, and the temporary impacts of short-lived aerosols and reactive greenhouse gases, the Earth’s climate is not equilibrated with anthropogenic forcing. As a result, even if fossil-fuel emissions were to suddenly cease, some level of committed warming is expected due to past emissions as studied previously using climate models. Here, we provide an observational-based quantification of this committed warming using the instrument record of global-mean warming, recently improved estimates of Earth’s energy imbalance, and estimates of radiative forcing from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Compared with pre-industrial levels, we find a committed warming of 1.5 K (0.9–3.6, 5th–95th percentile) at equilibrium, and of 1.3 K (0.9–2.3) within this century. However, when assuming that ocean carbon uptake cancels remnant greenhouse gas-induced warming on centennial timescales, committed warming is reduced to 1.1 K (0.7–1.8). In the latter case there is a 13% risk that committed warming already exceeds the 1.5 K target set in Paris. Regular updates of these observationally constrained committed warming estimates, although simplistic, can provide transparent guidance as uncertainty regarding transient climate sensitivity inevitably narrows and the understanding of the limitations of the framework is advanced.

Continued increase of extreme El Niño frequency long after 1.5 °C warming stabilization
Guojian Wang et al.
Nature Climate Change, August 2017, Pages 568–572

The Paris Agreement aims to constrain global mean temperature (GMT) increases to 2 °C above pre-industrial levels, with an aspirational target of 1.5 °C. However, the pathway to these targets and the impacts of a 1.5 °C and 2 °C warming on extreme El Niño and La Niña events — which severely influence weather patterns, agriculture, ecosystems, public health and economies — is little known. Here, by analysing climate models participating in the Climate Model Intercomparison Project’s Phase 5 (CMIP5) under a most likely emission scenario, we demonstrate that extreme El Niño frequency increases linearly with the GMT towards a doubling at 1.5 °C warming. This increasing frequency of extreme El Niño events continues for up to a century after GMT has stabilized, underpinned by an oceanic thermocline deepening that sustains faster warming in the eastern equatorial Pacific than the off-equatorial region. Ultimately, this implies a higher risk of extreme El Niño to future generations after GMT rise has halted. On the other hand, whereas previous research suggests extreme La Niña events may double in frequency under the 4.5 °C warming scenario, the results presented here indicate little to no change under 1.5 °C or 2 °C warming.

Sound physiological knowledge and principles in modeling shrinking of fishes under climate change
Daniel Pauly & William Cheung
Global Change Biology, forthcoming

One of the main expected responses of marine fishes to ocean warming is decrease in body size, as supported by evidence from empirical data and theoretical modeling. The theoretical underpinning for fish shrinking is that the oxygen supply to large fish size cannot be met by their gills, whose surface area cannot keep up with the oxygen demand by their three-dimensional bodies. However, Lefevre et al. (Global Change Biology, 2017, 23, 3449–3459) argue against such theory. Here, we re-assert, with the Gill-Oxygen Limitation Theory (GOLT), that gills, which must retain the properties of open surfaces because their growth, even while hyperallometric, cannot keep up with the demand of growing three-dimensional bodies. Also, we show that a wide range of biological features of fish and other water-breathing organisms can be understood when gill area limitation is used as an explanation. We also note that an alternative to GOLT, offering a more parsimonious explanation for these features of water-breathers has not been proposed. Available empirical evidence corroborates predictions of decrease in body sizes under ocean warming based on GOLT, with the magnitude of the predicted change increases when using more species-specific parameter values of metabolic scaling.

Changes in Winter North Atlantic Extratropical Cyclones in High-Resolution Regional Pseudo–Global Warming Simulations
Allison Michaelis et al.
Journal of Climate, September 2017, Pages 6905–6925

The present study investigates changes in the location, frequency, intensity, and dynamical processes of North Atlantic extratropical cyclones with warming consistent with the IPCC Fifth Assessment Report (AR5) representative concentration pathway 8.5 (RCP8.5) scenario. The modeling, analysis, and prediction (MAP) climatology of midlatitude storminess (MCMS) feature-tracking algorithm was utilized to analyze 10 cold-season high-resolution atmospheric simulations over the North Atlantic region in current and future climates. Enhanced extratropical cyclone activity is most evident in the northeast North Atlantic and off the U.S. East Coast. These changes in cyclone activity are offset from changes in eddy kinetic energy and eddy heat flux. Investigation of the minimum SLP reached at each grid point reveals a lack of correspondence between the strongest events in the current and future simulations, indicating the future simulations produced a different population of storms. Examination of the percent change of storms in the storm-track region shows a reduction in the number of strong storms (i.e., those reaching a minimum SLP perturbation of at least −51 hPa). Storm-relative composites of strong and moderate storms show an increase in precipitation, associated with enhanced latent heat release and strengthening of the 900–700-hPa layer-average potential vorticity (PV). Other structural changes found for cyclones in a future climate include weakened upper-level PV for strong storms and a weakened near-surface potential temperature anomaly for moderate storms, demonstrating a change in storm dynamics. Furthermore, the impacts associated with extratropical cyclones, such as strong near-surface winds and heavy precipitation, strengthen and become more frequent with warming.

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