Kevin Lewis

November 21, 2018

Urbanization exacerbated the rainfall and flooding caused by Hurricane Harvey in Houston
Wei Zhang et al.
Nature, 15 November 2018, Pages 384–388

Category 4 landfalling hurricane Harvey poured more than a metre of rainfall across the heavily populated Houston area, leading to unprecedented flooding and damage. Although studies have focused on the contribution of anthropogenic climate change to this extreme rainfall event, limited attention has been paid to the potential effects of urbanization on the hydrometeorology associated with hurricane Harvey. Here we find that urbanization exacerbated not only the flood response but also the storm total rainfall. Using the Weather Research and Forecast model — a numerical model for simulating weather and climate at regional scales — and statistical models, we quantify the contribution of urbanization to rainfall and flooding. Overall, we find that the probability of such extreme flood events across the studied basins increased on average by about 21 times in the period 25–30 August 2017 because of urbanization. The effect of urbanization on storm-induced extreme precipitation and flooding should be more explicitly included in global climate models, and this study highlights its importance when assessing the future risk of such extreme events in highly urbanized coastal areas.

Decreases in global beer supply due to extreme drought and heat
Wei Xie et al.
Nature Plants, November 2018, Pages 964–973

Beer is the most popular alcoholic beverage in the world by volume consumed, and yields of its main ingredient, barley, decline sharply in periods of extreme drought and heat. Although the frequency and severity of drought and heat extremes increase substantially in range of future climate scenarios by five Earth System Models, the vulnerability of beer supply to such extremes has never been assessed. We couple a process-based crop model (decision support system for agrotechnology transfer) and a global economic model (Global Trade Analysis Project model) to evaluate the effects of concurrent drought and heat extremes projected under a range of future climate scenarios. We find that these extreme events may cause substantial decreases in barley yields worldwide. Average yield losses range from 3% to 17% depending on the severity of the conditions. Decreases in the global supply of barley lead to proportionally larger decreases in barley used to make beer and ultimately result in dramatic regional decreases in beer consumption (for example, −32% in Argentina) and increases in beer prices (for example, +193% in Ireland). Although not the most concerning impact of future climate change, climate-related weather extremes may threaten the availability and economic accessibility of beer.

The Crucial Role of International Trade in Adaptation to Climate Change
Christophe Gouel & David Laborde
NBER Working Paper, November 2018

Climate change effects on agricultural yields will be uneven over the world with a few countries, mostly in high latitudes, that may experience gains, while most will see average yield decrease. This paper aims at quantifying the role of international trade in attenuating the effects of climate change by allowing the expression of the new climate-induced pattern of comparative advantages. To do this, we develop a quantitative general equilibrium trade model where the representation of acreage and land use choices is inspired from modern Ricardian trade models but also consistent with theoretical and empirical literature on land use choices. The model is calibrated on spatially explicit information about potential yields before and after climate change coming from the agronomic literature. The results show that the climate-induced yield changes generate large price movements that incentivize adjustments in acreage and trade. The new trade pattern is very different from the current one, showing the important role of trade flows in adapting to climate change. This is confirmed by larger welfare losses from climate change when adjustments in trade flows are constrained versus when they are not.

Broad threat to humanity from cumulative climate hazards intensified by greenhouse gas emissions
Camilo Mora et al.
Nature Climate Change, forthcoming

The ongoing emission of greenhouse gases (GHGs) is triggering changes in many climate hazards that can impact humanity. We found traceable evidence for 467 pathways by which human health, water, food, economy, infrastructure and security have been recently impacted by climate hazards such as warming, heatwaves, precipitation, drought, floods, fires, storms, sea-level rise and changes in natural land cover and ocean chemistry. By 2100, the world’s population will be exposed concurrently to the equivalent of the largest magnitude in one of these hazards if emissions are aggressively reduced, or three if they are not, with some tropical coastal areas facing up to six simultaneous hazards. These findings highlight the fact that GHG emissions pose a broad threat to humanity by intensifying multiple hazards to which humanity is vulnerable.

Impacts of a Carbon Tax across US Household Income Groups: What Are the Equity-Efficiency Trade-Offs?
Lawrence Goulder et al.
NBER Working Paper, October 2018

This paper assesses the impacts across US household income groups of carbon taxes of various designs. We consider both the source-side impacts (reflecting how policies affect nominal wage, capital, and transfer incomes) and the use-side impacts (reflecting how policies alter prices of goods and services purchased by households). We apply an integrated general equilibrium framework with extended measures of the source- and use-side impacts that add up to the overall welfare impact. The distributional impacts depend importantly on the revenue recycling method and treatment of transfer income. In the absence of compensation targeted to particular income groups, use-side impacts tend to be regressive and source-side impacts progressive, with the progressive source-side impacts fully offsetting the regressive use-side impacts. Both types of impact are considerably larger under our more comprehensive welfare measures than under more conventional measures. The efficiency costs of targeted compensation to achieve distributional objectives depend critically on the recycling method and compensation target. These costs are an order of magnitude higher when the revenues that remain after compensation are used for corporate income tax cuts than when the remaining revenues are used in other ways. Efficiency costs rise dramatically when targeted compensation extends beyond the lowest income quintiles.

Anthropogenic influences on major tropical cyclone events
Christina Patricola & Michael Wehner
Nature, 15 November 2018, Pages 339–346

There is no consensus on whether climate change has yet affected the statistics of tropical cyclones, owing to their large natural variability and the limited period of consistent observations. In addition, projections of future tropical cyclone activity are uncertain, because they often rely on coarse-resolution climate models that parameterize convection and hence have difficulty in directly representing tropical cyclones. Here we used convection-permitting regional climate model simulations to investigate whether and how recent destructive tropical cyclones would change if these events had occurred in pre-industrial and in future climates. We found that, relative to pre-industrial conditions, climate change so far has enhanced the average and extreme rainfall of hurricanes Katrina, Irma and Maria, but did not change tropical cyclone wind-speed intensity. In addition, future anthropogenic warming would robustly increase the wind speed and rainfall of 11 of 13 intense tropical cyclones (of 15 events sampled globally). Additional regional climate model simulations suggest that convective parameterization introduces minimal uncertainty into the sign of projected changes in tropical cyclone intensity and rainfall, which allows us to have confidence in projections from global models with parameterized convection and resolution fine enough to include tropical cyclones.

Effects of Climate Change on Wind-Driven Heavy-Snowfall Events over Eastern North America
Tyler Janoskia et al.
Journal of Climate, November 2018, Pages 9037–9054

Eastern North America contains densely populated, highly developed areas, making winter storms with strong winds and high snowfall among the costliest storm types. For this reason, it is important to determine how the frequency of high-impact winter storms, specifically, those combining significant snowfall and winds, will change in this region under increasing greenhouse gas concentrations. This study uses a high-resolution coupled global climate model to simulate the changes in extreme winter conditions from the present climate to a future scenario with doubled CO2 concentrations (2XC). In particular, this study focuses on changes in high-snowfall, extreme-wind (HSEW) events, which are defined as the occurrence of 2-day snowfall and high winds exceeding thresholds based on extreme values from the control simulation, where greenhouse gas concentrations remain fixed. Mean snowfall consistently decreases across the entire region, but extreme snowfall shows a more inconsistent pattern, with some areas experiencing increases in the frequency of extreme-snowfall events. Extreme-wind events show relatively small changes in frequency with 2XC, with the exception of high-elevation areas where there are large decreases in frequency. As a result of combined changes in wind and snowfall, HSEW events decrease in frequency in the 2XC simulation for much of eastern North America. Changes in the number of HSEW events in the 2XC environment are driven mainly by changes in the frequency of extreme-snowfall events, with most of the region experiencing decreases in event frequency, except for certain inland areas at higher latitudes.


Poleward migration of the destructive effects of tropical cyclones during the 20th century
Jan Altman et al.
Proceedings of the National Academy of Sciences, 6 November 2018, Pages 11543-11548

Determination of long-term tropical cyclone (TC) variability is of enormous importance to society; however, changes in TC activity are poorly understood owing to discrepancies among various datasets and limited span of instrumental records. While the increasing intensity and frequency of TCs have been previously documented on a long-term scale using various proxy records, determination of their poleward migration has been based mostly on short-term instrumental data. Here we present a unique tree-ring–based approach for determination of long-term variability in TC activity via forest disturbance rates in northeast Asia (33–45°N). Our results indicate significant long-term changes in TC activity, with increased rates of disturbances in the northern latitudes over the past century. The disturbance frequency was stable over time in the southern latitudes, however. Our findings of increasing disturbance frequency in the areas formerly situated at the edge of TC activity provide evidence supporting the broad relevance of poleward migration of TCs. Our results significantly enhance our understanding of the effects of climate change on TCs and emphasize the need for determination of long-term variation of past TC activity to improve future TC projections.

Spatial trends in United States tornado frequency
Vittorio Gensini & Harold Brooks
npj Climate and Atmospheric Science, October 2018

Severe thunderstorms accompanied by tornadoes, hail, and damaging winds cause an average of 5.4 billion dollars of damage each year across the United States, and 10 billion-dollar events are no longer uncommon. This overall economic and casualty risk—with over 600 severe thunderstorm related deaths in 2011—has prompted public and scientific inquiries about the impact of climate change on tornadoes. We show that national annual frequencies of tornado reports have remained relatively constant, but significant spatially-varying temporal trends in tornado frequency have occurred since 1979. Negative tendencies of tornado occurrence have been noted in portions of the central and southern Great Plains, while robust positive trends have been documented in portions of the Midwest and Southeast United States. In addition, the significant tornado parameter is used as an environmental covariate to increase confidence in the tornado report results.

“Ticking Bomb”: The Impact of Climate Change on the Incidence of Lyme Disease
Igor Dumic & Edson Severnini
Canadian Journal of Infectious Diseases and Medical Microbiology, October 2018

Lyme disease (LD) is the most common tick-borne disease in North America. It is caused by Borrelia burgdorferi and transmitted to humans by blacklegged ticks, Ixodes scapularis. The life cycle of the LD vector, I. scapularis, usually takes two to three years to complete and goes through three stages, all of which are dependent on environmental factors. Increases in daily average temperatures, a manifestation of climate change, might have contributed to an increase in tick abundance via higher rates of tick survival. Additionally, these environmental changes might have contributed to better host availability, which is necessary for tick feeding and life cycle completion. In fact, it has been shown that both tick activity and survival depend on temperature and humidity. In this study, we have examined the relationship between those climatic variables and the reported incidence of LD in 15 states that contribute to more than 95% of reported cases within the Unites States. Using fixed effects analysis for a panel of 468 U.S. counties from those high-incidence states with annual data available for the period 2000–2016, we have found sizable impacts of temperature on the incidence of LD. Those impacts can be described approximately by an inverted U-shaped relationship, consistent with patterns of tick survival and host-seeking behavior. Assuming a 2°C increase in annual average temperature — in line with mid-century (2036–2065) projections from the latest U.S. National Climate Assessment (NCA4) — we have predicted that the number of LD cases in the United States will increase by over 20 percent in the coming decades. These findings may help improving preparedness and response by clinicians, public health professionals, and policy makers, as well as raising public awareness of the importance of being cautious when engaging in outdoor activities.

Substantial Increase in Heat Wave Risks in China in a Future Warmer World
Ying Sun, Ting Hu & Xuebin Zhang
Earth's Future, forthcoming

Increases in the frequency and intensity of heat waves have serious impacts on human health, agriculture, energy and infrastructure. Here we use three simple metrics including the number of heat wave days, the length of heat wave season, and the annual hottest day temperature to characterize future changes in heat wave severity in China, based on large ensemble simulations conducted with the Canadian Earth System Model Version 2 (CanESM2) in the context of emergency preparedness. A heat wave day is defined as a day with daily maximum temperature reaching heat alert level (35 °C). We find that global warming is associated with more severe heat waves including more heat wave days, longer heat wave season and higher hottest day temperature, and expansion of regions impacted by heat waves. While the increase in the magnitude of extremes in heat wave metrics with global warming level is close to linear, the increase in the frequency of extremes is much faster. For example, the historically hottest summer in 2013 in Eastern China, which occurs about one in 5 years in the 2013 climate, is projected to become more frequent than one in 2 years under 1.5 °C global warming and almost every year would be worse than 2013 under 2 °C warming. Additionally, the increase in the frequency of the extreme events is larger for rarer extremes. The frequencies for once‐in‐5‐year, once‐in‐10‐year, and once‐in‐50‐year events increase by 2.5, 3.5, and 5.5 times under 1.5 °C global warming, respectively.

Quantification of ocean heat uptake from changes in atmospheric O2 and CO2 composition
Laure Resplandy et al.
Nature, 1 November 2018, Pages 105–108

The ocean is the main source of thermal inertia in the climate system. During recent decades, ocean heat uptake has been quantified by using hydrographic temperature measurements and data from the Argo float program, which expanded its coverage after 2007. However, these estimates all use the same imperfect ocean dataset and share additional uncertainties resulting from sparse coverage, especially before 2007. Here we provide an independent estimate by using measurements of atmospheric oxygen (O2) and carbon dioxide (CO2) — levels of which increase as the ocean warms and releases gases — as a whole-ocean thermometer. We show that the ocean gained 1.33 ± 0.20 × 10^22 joules of heat per year between 1991 and 2016, equivalent to a planetary energy imbalance of 0.83 ± 0.11 watts per square metre of Earth’s surface. We also find that the ocean-warming effect that led to the outgassing of O2 and CO2 can be isolated from the direct effects of anthropogenic emissions and CO2 sinks. Our result — which relies on high-precision O2 measurements dating back to 1991 — suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth response to climate change, such as climate sensitivity to greenhouse gases and the thermal component of sea-level rise.


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