Findings

Taking heat

Kevin Lewis

July 12, 2017

Does the label really matter? Evidence that the US public continues to doubt “global warming” more than “climate change”
Jonathon Schuldt, Peter Enns & Victoria Cavaliere
Climatic Change, July 2017, Pages 271–280

Abstract:

Does the public doubt the existence of “global warming” more than “climate change”? While previously published research suggests that it does, others have argued that this effect either never existed or has disappeared amid broader shifts in public opinion. We draw on survey response theory to help reconcile this debate. We then analyze data from an October 2016 probability-based survey experiment (n = 1461 US adults) to test the prediction that the US public (and particularly, Republicans) continue to respond differently when asked whether global warming vs. climate change exists. Indeed, respondents who were asked about climate change responded “Yes” (definitely or somewhat) more often (85.8%) than respondents who were asked about global warming (80.9%), an effect observed for Republicans (74.4 vs. 65.5%) but not Democrats (94% in both conditions). We discuss broader implications for US public opinion and discourse in an era of significant proposed government rollbacks of climate and environmental policy.


Evaluation of a proposal for reliable low-cost grid power with 100% wind, water, and solar
Christopher Clack et al.
Proceedings of the National Academy of Sciences, 27 June 2017, Pages 6722–6727

Abstract:

A number of analyses, meta-analyses, and assessments, including those performed by the Intergovernmental Panel on Climate Change, the National Oceanic and Atmospheric Administration, the National Renewable Energy Laboratory, and the International Energy Agency, have concluded that deployment of a diverse portfolio of clean energy technologies makes a transition to a low-carbon-emission energy system both more feasible and less costly than other pathways. In contrast, Jacobson et al. [Jacobson MZ, Delucchi MA, Cameron MA, Frew BA (2015) Proc Natl Acad Sci USA 112(49):15060–15065] argue that it is feasible to provide “low-cost solutions to the grid reliability problem with 100% penetration of WWS [wind, water and solar power] across all energy sectors in the continental United States between 2050 and 2055”, with only electricity and hydrogen as energy carriers. In this paper, we evaluate that study and find significant shortcomings in the analysis. In particular, we point out that this work used invalid modeling tools, contained modeling errors, and made implausible and inadequately supported assumptions. Policy makers should treat with caution any visions of a rapid, reliable, and low-cost transition to entire energy systems that relies almost exclusively on wind, solar, and hydroelectric power.


Global risk of deadly heat
Camilo Mora et al.
Nature Climate Change, July 2017, Pages 501–506

Abstract:

Climate change can increase the risk of conditions that exceed human thermoregulatory capacity. Although numerous studies report increased mortality associated with extreme heat events, quantifying the global risk of heat-related mortality remains challenging due to a lack of comparable data on heat-related deaths. Here we conducted a global analysis of documented lethal heat events to identify the climatic conditions associated with human death and then quantified the current and projected occurrence of such deadly climatic conditions worldwide. We reviewed papers published between 1980 and 2014, and found 783 cases of excess human mortality associated with heat from 164 cities in 36 countries. Based on the climatic conditions of those lethal heat events, we identified a global threshold beyond which daily mean surface air temperature and relative humidity become deadly. Around 30% of the world’s population is currently exposed to climatic conditions exceeding this deadly threshold for at least 20 days a year. By 2100, this percentage is projected to increase to ~48% under a scenario with drastic reductions of greenhouse gas emissions and ~74% under a scenario of growing emissions. An increasing threat to human life from excess heat now seems almost inevitable, but will be greatly aggravated if greenhouse gases are not considerably reduced.


Estimating economic damage from climate change in the United States
Solomon Hsiang et al.
Science, 30 June 2017, Pages 1362-1369

Abstract:

Estimates of climate change damage are central to the design of climate policies. Here, we develop a flexible architecture for computing damages that integrates climate science, econometric analyses, and process models. We use this approach to construct spatially explicit, probabilistic, and empirically derived estimates of economic damage in the United States from climate change. The combined value of market and nonmarket damage across analyzed sectors — agriculture, crime, coastal storms, energy, human mortality, and labor — increases quadratically in global mean temperature, costing roughly 1.2% of gross domestic product per +1°C on average. Importantly, risk is distributed unequally across locations, generating a large transfer of value northward and westward that increases economic inequality. By the late 21st century, the poorest third of counties are projected to experience damages between 2 and 20% of county income (90% chance) under business-as-usual emissions (Representative Concentration Pathway 8.5).


Substituting beans for beef as a contribution toward US climate change targets
Helen Harwatt et al.
Climatic Change, July 2017, Pages 261–270

Abstract:

Shifting dietary patterns for environmental benefits has long been advocated. In relation to mitigating climate change, the debate has been more recent, with a growing interest from policy makers, academics, and society. Many researchers have highlighted the need for changes to food consumption in order to achieve the required greenhouse gas (GHG) reductions. So far, food consumption has not been anchored in climate change policy to the same extent as energy production and usage, nor has it been considered within the context of achieving GHG targets to a level where tangible outputs are available. Here, we address those issues by performing a relatively simple analysis that considers the extent to which one food exchange could contribute to achieving GHG reduction targets in the United States (US). We use the targeted reduction for 2020 as a reference and apply published Life Cycle Assessment data on GHG emissions to beans and beef consumed in the US. We calculate the difference in GHGs resulting from the replacement of beef with beans in terms of both calories and protein. Our results demonstrate that substituting one food for another, beans for beef, could achieve approximately 46 to 74% of the reductions needed to meet the 2020 GHG target for the US. In turn, this shift would free up 42% of US cropland (692,918 km2). While not currently recognized as a climate policy option, the “beans for beef” scenario offers significant climate change mitigation and other environmental benefits, illustrating the high potential of animal to plant food shifts.


The changing hail threat over North America in response to anthropogenic climate change
Julian Brimelow, William Burrows & John Hanesiak
Nature Climate Change, July 2017, Pages 516–522

Abstract:

Anthropogenic climate change is anticipated to increase severe thunderstorm potential in North America, but the resulting changes in associated convective hazards are not well known. Here, using a novel modelling approach, we investigate the spatiotemporal changes in hail frequency and size between the present (1971–2000) and future (2041–2070). Although fewer hail days are expected over most areas in the future, an increase in the mean hail size is projected, with fewer small hail events and a shift toward a more frequent occurrence of larger hail. This leads to an anticipated increase in hail damage potential over most southern regions in spring, retreating to the higher latitudes (that is, north of 50° N) and the Rocky Mountains in the summer. In contrast, a dramatic decrease in hail frequency and damage potential is predicted over eastern and southeastern regions in spring and summer due to a significant increase in melting that mitigates gains in hail size from increased buoyancy.


Willingness to Pay for Low Water Footprint Food Choices During Drought
Hannah Krovetz, Rebecca Taylor & Sofia Villas-Boas
NBER Working Paper, June 2017

Abstract:

In the context of recent California drought years, we investigate empirically whether consumers are willing to pay for more efficient water usage in the production of four California agricultural products. We implement an internet survey choice experiment for avocados, almonds, lettuce, and tomatoes to elicit consumer valuation for water efficiency via revealed choices. We estimate a model of consumer choices where a product is defined as a bundle of three attributes: price, production method (conventional or organic), and water usage (average or efficient). Varying the attribute space presented to consumers in the experimental choice design gives us the data variation to estimate a discrete choice model — both conditional logit specifications and random coefficient mixed logit specifications. We find that on average consumers have a significant positive marginal utility towards water-efficiency and estimate that there is an implied positive willingness to pay (WTP) of about 12 cents per gallon of water saved on average. Moreover, informing consumers about the drought severity increases the WTP for low water footprint options, but not significantly. We find that there is heterogeneity in the WTP along respondents' education, race, and also with respect to stated environmental concern. Our findings have policy implications in that they suggest there to be a market based potential to nudge consumers who want to decrease their water footprint and follow a more sustainable diet, namely, by revealing information on the product's water footprint in a form of a label. Simulations of removing low water footprint labels from the choice set attributes imply significant consumer surplus losses, especially for the more educated, white, and more environmentally concerned respondents.


The increasing rate of global mean sea-level rise during 1993–2014
Xianyao Chen et al.
Nature Climate Change, July 2017, Pages 492–495

Abstract:

Global mean sea level (GMSL) has been rising at a faster rate during the satellite altimetry period (1993–2014) than previous decades, and is expected to accelerate further over the coming century. However, the accelerations observed over century and longer periods have not been clearly detected in altimeter data spanning the past two decades. Here we show that the rise, from the sum of all observed contributions to GMSL, increases from 2.2 ± 0.3 mm yr−1 in 1993 to 3.3 ± 0.3 mm yr−1 in 2014. This is in approximate agreement with observed increase in GMSL rise, 2.4 ± 0.2 mm yr−1 (1993) to 2.9 ± 0.3 mm yr−1 (2014), from satellite observations that have been adjusted for small systematic drift, particularly affecting the first decade of satellite observations. The mass contributions to GMSL increase from about 50% in 1993 to 70% in 2014 with the largest, and statistically significant, increase coming from the contribution from the Greenland ice sheet, which is less than 5% of the GMSL rate during 1993 but more than 25% during 2014. The suggested acceleration and improved closure of the sea-level budget highlights the importance and urgency of mitigating climate change and formulating coastal adaption plans to mitigate the impacts of ongoing sea-level rise.


A novel proxy and the sea level rise in Venice, Italy, from 1350 to 2014
Dario Camuffo, Chiara Bertolin & Patrizia Schenal
Climatic Change, July 2017, Pages 73–86

Abstract:

The evolution of relative sea level (RSL) in Venice, Italy, is crucial for the safeguarding of the city and it is now possible to extend our knowledge back to 1350, including the whole Little Ice Age and modern global warming. The existing tide gauge record is extensive, going back to 1871, but it is affected by the superposition of multidecadal swings and short-term fluctuations, including both natural and manmade forcing factors. A biological proxy, i.e. the green algae belt reported on paintings made with the help of a camera obscura by the Venetian painters Canaletto and Bellotto (eighteenth century) and Veronese (sixteenth century), helps us to go back to 1571. This paper presents an exceptionally long series (i.e. 664 years) and adds a novel proxy: the submersion of water stairs of the historic palaces facing the Grand Canal. Originally, the bottom step of the water stairs was built in relation to the sea level and the slippery algae belt, while today, the water stairs are mostly submerged. An underwater survey of 78 water stairs has provided new data about the RSL since 1350. The results show that RSL in Venice was always rising at an increasingly fast rate. By subtracting local land subsidence (LLS) from RSL, absolute (eustatic) sea level (ASL) has been calculated. For both RSL and ASL, the apparent acceleration is +0.0030 ± 0.0004 mm year−2. This figure becomes unstable when the record length is reduced. A discussion is made about the interpolation functions, i.e. the second-order polynomial and the exponential that provide almost the same best-fit over the common period. The RSL and ASL trend lines and the possibility of turning points are also discussed and compared with other scholarly studies. A eustatic turning point is suggested for the mid fifteenth century, consistent with the literature. However, the comparison between scholarly papers is difficult due to geographic and geological differences between sites and record durations.


A human-driven decline in global burned area
Niels Andela et al.
Science, 30 June 2017, Pages 1356-1362

Abstract:

Fire is an essential Earth system process that alters ecosystem and atmospheric composition. Here we assessed long-term fire trends using multiple satellite data sets. We found that global burned area declined by 24.3 ± 8.8% over the past 18 years. The estimated decrease in burned area remained robust after adjusting for precipitation variability and was largest in savannas. Agricultural expansion and intensification were primary drivers of declining fire activity. Fewer and smaller fires reduced aerosol concentrations, modified vegetation structure, and increased the magnitude of the terrestrial carbon sink. Fire models were unable to reproduce the pattern and magnitude of observed declines, suggesting that they may overestimate fire emissions in future projections. Using economic and demographic variables, we developed a conceptual model for predicting fire in human-dominated landscapes.


El Niño-like teleconnection increases California precipitation in response to warming
Robert Allen & Rainer Luptowitz
Nature Communications, July 2017

Abstract:

Future California (CA) precipitation projections, including those from the most recent Climate Model Intercomparison Project (CMIP5), remain uncertain. This uncertainty is related to several factors, including relatively large internal climate variability, model shortcomings, and because CA lies within a transition zone, where mid-latitude regions are expected to become wetter and subtropical regions drier. Here, we use a multitude of models to show CA may receive more precipitation in the future under a business-as-usual scenario. The boreal winter season-when most of the CA precipitation increase occurs-is associated with robust changes in the mean circulation reminiscent of an El Niño teleconnection. Using idealized simulations with two different models, we further show that warming of tropical Pacific sea surface temperatures accounts for these changes. Models that better simulate the observed El Niño-CA precipitation teleconnection yield larger, and more consistent increases in CA precipitation through the twenty-first century.


Is Current Irrigation Sustainable in the United States? An Integrated Assessment of Climate Change Impact on Water Resources and Irrigated Crop Yields
Elodie Blanc et al.
Earth's Future, forthcoming

Abstract:

While climate change impacts on crop yields has been extensively studied, estimating the impact of water shortages on irrigated crop yields is challenging because the water resources management system is complex. To investigate this issue, we integrate a crop yield reduction module and a water resources model into the MIT Integrated Global System Modeling (IGSM) framework, an integrated assessment model linking a global economic model to an Earth system model. We assess the effects of climate and socio-economic changes on water availability for irrigation in the US as well as subsequent impacts on crop yields by 2050, while accounting for climate change projection uncertainty. We find that climate and socio-economic changes will increase water shortages and strongly reduce irrigated yields for specific crops (i.e. cotton and forage), or in specific regions (i.e the Southwest) where irrigation is not sustainable. Crop modeling studies that do not represent changes in irrigation availability can thus be misleading. Yet, since the most water-stressed basins represent a relatively small share of US irrigated areas, the overall reduction in US crop yields is small. The response of crop yields to climate change and water stress also suggests that some level of adaptation will be feasible, like relocating croplands to regions with sustainable irrigation or switching to less irrigation intensive crops. Finally, additional simulations show that greenhouse gas (GHG) mitigation can alleviate the effect of water stress on irrigated crop yields, enough to offset the reduced CO2 fertilization effect compared to an unconstrained GHG emission scenario.


Towards a balanced view of Arctic shipping: Estimating economic impacts of emissions from increased traffic on the Northern Sea Route
Dmitry Yumashev et al.
Climatic Change, July 2017, Pages 143–155

Abstract:

The extensive melting of Arctic sea ice driven by climate change provides opportunities for commercial shipping due to shorter travel distances of up to 40% between Asia and Europe. It has been estimated that around 5% of the world’s trade could be shipped through the Northern Sea Route (NSR) in the Arctic alone under year-round and unhampered navigability, generating additional income for many European and East Asian countries. Our analysis shows that for Arctic sea ice conditions under the RCP8.5 emissions scenario and business restrictions facing shipping companies, NSR traffic will increase steadily from the mid-2030s onwards, although it will take over a century to reach the full capacity expected for ice-free conditions. However, in order to achieve a balanced view of Arctic shipping, it is important to include its detrimental environmental impacts, most notably emissions of short-lived pollutants such as black carbon, as well as CO2 and non-CO2 emissions associated with the additional economic growth enabled by NSR. The total climate feedback of NSR could contribute 0.05% (0.04%) to global mean temperature rise by 2100 under RCP8.5 (RCP4.5), adding $2.15 trillion ($0.44 trillion) to the NPV of total impacts of climate change over the period until 2200 for the SSP2 socio-economic scenario. The climatic losses offset 33% (24.7%) of the total economic gains from NSR under RCP8.5 (RCP4.5), with the biggest losses set to occur in Africa and India. These findings call for policy instruments aimed at reducing emissions from Arctic shipping and providing compensation to the affected regions.


Climatic warming in China during 1901–2015 based on an extended dataset of instrumental temperature records
Lijuan Cao et al.
Environmental Research Letters, June 2016

Abstract:

Monthly mean instrumental surface air temperature (SAT) observations back to the nineteenth century in China are synthesized from different sources via specific quality-control, interpolation, and homogenization. Compared with the first homogenized long-term SAT dataset for China by Cao et al (2013), which contained 18 stations mainly located in the middle and eastern part of China, the present dataset includes homogenized monthly SAT series at 32 stations, with an extended coverage especially towards western China. Missing values are interpolated by using observations at nearby stations, including those from neighboring countries. Cross validation shows that the mean bias error (MBE) is generally small and falls between 0.45 °C and −0.35 °C. Multiple homogenization methods and available metadata are applied to assess the consistency of the time series and to adjust inhomogeneity biases. The homogenized annual mean SAT series shows a range of trends between 1.1 °C and 4.0 °C/century in northeastern China, between 0.4 °C and 1.9 °C/century in southeastern China, and between 1.4 °C and 3.7 °C/century in western China to the west of 105 E (from the initial years of the stations to 2015). The unadjusted data include unusually warm records during the 1940s and hence tend to underestimate the warming trends at a number of stations. The mean SAT series for China based on the climate anomaly method shows a warming trend of 1.56 °C/century during 1901–2015, larger than those based on other currently available datasets.


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