Kevin Lewis

November 25, 2020

Global food system emissions could preclude achieving the 1.5° and 2°C climate change targets
Michael Clark et al.
Science, 6 November 2020, Pages 705-708


The Paris Agreement’s goal of limiting the increase in global temperature to 1.5° or 2°C above preindustrial levels requires rapid reductions in greenhouse gas emissions. Although reducing emissions from fossil fuels is essential for meeting this goal, other sources of emissions may also preclude its attainment. We show that even if fossil fuel emissions were immediately halted, current trends in global food systems would prevent the achievement of the 1.5°C target and, by the end of the century, threaten the achievement of the 2°C target. Meeting the 1.5°C target requires rapid and ambitious changes to food systems as well as to all nonfood sectors. The 2°C target could be achieved with less-ambitious changes to food systems, but only if fossil fuel and other nonfood emissions are eliminated soon.

Learning is inhibited by heat exposure, both internationally and within the United States
Jisung Park, Joshua Goodman & Patrick Behrer
Nature Human Behaviour, forthcoming


Human capital generally, and cognitive skills specifically, play a crucial role in determining economic mobility and macroeconomic growth. While elevated temperatures have been shown to impair short-run cognitive performance, much less is known about whether heat exposure affects the rate of skill formation. We combine standardized achievement data for 58 countries and 12,000 US school districts with detailed weather and academic calendar information to show that the rate of learning decreases with an increase in the number of hot school days. These results provide evidence that climatic differences may contribute to differences in educational achievement both across countries and within countries by socioeconomic status and that may have important implications for the magnitude and functional form of climate damages in coupled human-natural systems.

Voting with their Sandals: Partisan Residential Sorting on Climate Change Risk
Asaf Bernstein et al.
NBER Working Paper, October 2020


Climate change partisanship is reflected in residential choice. Comparing individual occupants at properties in the same zip code with similar elevation and proximity to the coast, registered republicans (democrats) are more (less) likely than independents to own houses exposed to sea level rise (SLR). Findings are unchanged controlling flexibly for other individual demographics and a variety of granular property characteristics, including the value of the home. This sorting is driven by differential perceptions of long-run SLR risks across the political spectrum not tolerance for current flood risk or preferences for correlated coastal amenities. Observed residential sorting manifests among owners regardless of occupancy, but not among renters. We also find no residential sorting in relation to storm surge exposure, which is a primary driver of current flood risk. Anticipatory sorting on climate change informs models of migration in the face of long-run risks and suggests households that are most likely to vote against climate friendly policies and least likely to adapt may ultimately bear the burden of climate change.

Solar geoengineering may not prevent strong warming from direct effects of CO2 on stratocumulus cloud cover
Tapio Schneider, Colleen Kaul & Kyle Pressel
Proceedings of the National Academy of Sciences, forthcoming


Discussions of countering global warming with solar geoengineering assume that warming owing to rising greenhouse-gas concentrations can be compensated by artificially reducing the amount of sunlight Earth absorbs. However, solar geoengineering may not be fail-safe to prevent global warming because CO2 can directly affect cloud cover: It reduces cloud cover by modulating the longwave radiative cooling within the atmosphere. This effect is not mitigated by solar geoengineering. Here, we use idealized high-resolution simulations of clouds to show that, even under a sustained solar geoengineering scenario with initially only modest warming, subtropical stratocumulus clouds gradually thin and may eventually break up into scattered cumulus clouds, at concentrations exceeding 1,700 parts per million (ppm). Because stratocumulus clouds cover large swaths of subtropical oceans and cool Earth by reflecting incident sunlight, their loss would trigger strong (about 5 K) global warming. Thus, the results highlight that, at least in this extreme and idealized scenario, solar geoengineering may not suffice to counter greenhouse-gas-driven global warming.

Constant carbon pricing increases support for climate action compared to ramping up costs over time
Michael Bechtel, Kenneth Scheve & Elisabeth van Lieshout
Nature Climate Change, November 2020, Pages 1004-1009


The introduction of policies that increase the price of carbon is central to limiting the adverse effects of global warming. Conventional wisdom holds that, of the possible cost paths, gradually raising costs relating to climate action will receive the most public support. Here, we explore mass support for dynamic cost paths in four major economies (France, Germany, the United Kingdom and the United States). We find that, for a given level of average costs, increasing cost paths receive little support whereas constant cost schedules are backed by majorities in all countries irrespective of whether those average costs are low or high. Experimental evidence indicates that constant cost paths significantly reduce opposition to climate action relative to increasing cost paths. Preferences for climate cost paths are related to the time horizons of individuals and their desire to smooth consumption over time.

Slower decay of landfalling hurricanes in a warming world
Lin Li & Pinaki Chakraborty
Nature, 12 November 2020, Pages 230-234


When a hurricane strikes land, the destruction of property and the environment and the loss of life are largely confined to a narrow coastal area. This is because hurricanes are fuelled by moisture from the ocean, and so hurricane intensity decays rapidly after striking land. In contrast to the effect of a warming climate on hurricane intensification, many aspects of which are fairly well understood, little is known of its effect on hurricane decay. Here we analyse intensity data for North Atlantic landfalling hurricanes over the past 50 years and show that hurricane decay has slowed, and that the slowdown in the decay over time is in direct proportion to a contemporaneous rise in the sea surface temperature. Thus, whereas in the late 1960s a typical hurricane lost about 75 per cent of its intensity in the first day past landfall, now the corresponding decay is only about 50 per cent. We also show, using computational simulations, that warmer sea surface temperatures induce a slower decay by increasing the stock of moisture that a hurricane carries as it hits land. This stored moisture constitutes a source of heat that is not considered in theoretical models of decay. Additionally, we show that climate-modulated changes in hurricane tracks contribute to the increasingly slow decay. Our findings suggest that as the world continues to warm, the destructive power of hurricanes will extend progressively farther inland.

Projected Changes in Reference Evapotranspiration in California and Nevada: Implications for Drought and Wildland Fire Danger
Daniel McEvoy et al.
Earth's Future, forthcoming


Recent high impact wildfires and droughts in California and Nevada have been linked to extremes in the Evaporative Demand Drought Index (EDDI) and Standardized Precipitation Evapotranspiration Index (SPEI), respectively. Both indices are dependent on reference evapotranspiration (ET0). Future changes in ET0 for California and Nevada are examined, calculated from global climate model simulations downscaled by Localized Constructed Analogs (LOCA). ET0 increases of 13‐18% at seasonal time scales are projected by late century (2070‐2099), with greatest relative increases in winter and spring. Seasonal ET0 increases are most strongly driven by warmer temperatures, with increasing specific humidity having a smaller, but noteworthy, counter tendency. Extreme (95th percentile) EDDI values on the two‐week timescale have coincided with recent large wildfires in the area. Two‐week EDDI extremes are projected to increase by 6‐10 times during summer and 4‐6 times during autumn by the end of the century. On multi‐year timescales, the occurrence of extreme droughts based on 3‐year SPEI below the historical 5th percentile, similar to that experienced during the 2012‐2016 drought across the region, is projected to increase 3‐15 times by late century. Positive trends in extreme multi‐year droughts will further increase seasonal fire potential through degraded forests and increased fuel loads and flammability. Understanding how these drought metrics change on various climate timescales at the local level can provide fundamental information to support the development of long‐term adaptation strategies for wildland fire and water resource management.

Government effectiveness and institutions as determinants of tropical cyclone mortality
Elizabeth Tennant & Elisabeth Gilmore
Proceedings of the National Academy of Sciences, 17 November 2020, Pages 28692-28699


Strong institutions as well as economic development are generally understood to play critical roles in protecting societies from the adverse impacts of natural hazards, such as tropical cyclones. The independent effect of institutions on reducing these risks, however, has not been confirmed empirically in previous global studies. As a storm’s path and intensity influence the severity of the damages and may be spatially correlated with human vulnerabilities, failing to accurately capture physical exposure in an econometric analysis may result in imprecise and biased estimates of the influence of the independent variables. Here, we develop an approach to control for physical exposure by spatially interacting meteorological and socioeconomic data for over 1,000 tropical cyclone disasters from 1979 to 2016. We find evidence that higher levels of national government effectiveness are associated with lower tropical cyclone mortality, even when controlling for average income and other socioeconomic conditions. Within countries, deaths are higher when strong winds are concentrated over areas of the country with elevated infant mortality rates, an indicator of institutional effectiveness through public service delivery. These results suggest that policies and programs to enhance institutional capacity and governance can support risk reduction from extreme weather events.

Sources of Cost Overrun in Nuclear Power Plant Construction Call for a New Approach to Engineering Design
Philip Eash-Gates et al.
Joule, 18 November 2020, Pages 2348-2373


Nuclear plant costs in the US have repeatedly exceeded projections. Here, we use data covering 5 decades and bottom-up cost modeling to identify the mechanisms behind this divergence. We observe that nth-of-a-kind plants have been more, not less, expensive than first-of-a-kind plants. “Soft” factors external to standardized reactor hardware, such as labor supervision, contributed over half of the cost rise from 1976 to 1987. Relatedly, containment building costs more than doubled from 1976 to 2017, due only in part to safety regulations. Labor productivity in recent plants is up to 13 times lower than industry expectations. Our results point to a gap between expected and realized costs stemming from low resilience to time- and site-dependent construction conditions. Prospective models suggest reducing commodity usage and automating construction to increase resilience. More generally, rethinking engineering design to relate design variables to cost change mechanisms could help deliver real-world cost reductions for technologies with demanding construction requirements.


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