Findings

Warm feelings

Kevin Lewis

March 02, 2016

Communicating the Scientific Consensus on Human-Caused Climate Change is an Effective and Depolarizing Public Engagement Strategy: Experimental Evidence from a Large National Replication Study

Sander van der Linden, Anthony Leiserowitz & Edward Maibach

Princeton University Working Paper, February 2016

Abstract:
This experimental study evaluated whether communicating the scientific consensus on human-caused climate change is likely to be effective with the American public. Drawing on a large national sample (N = 6,301), we set out to replicate and extend the findings of van der Linden et al. (2015). Consistent with the original study, we find robust and replicated evidence that communicating the scientific consensus on human-caused climate change leads to significant and substantial changes in perceived scientific agreement among conservatives, moderates, and liberals alike. These findings prove robust, even among those predisposed to receive counter-attitudinal information (e.g., Fox-news watchers, global warming skeptics). Further, among conservatives, we find the greatest change in perceived consensus among the subset whose own friends and family are least likely to believe in human-caused global warming. In short, we find little evidence of identity-protective cognition and no evidence of belief polarization across these groups. We further find that communicating the scientific consensus has (positive) direct effects (across the political spectrum) on belief that climate change is happening, human-caused, and a serious threat that requires societal action. We also find that these direct effects are mediated by changes in perceived scientific consensus. In other words, public perception of the scientific consensus is an important gateway cognition. Results also show that belief in the scientific consensus is more influential in driving public engagement than perceived consensus among other groups (e.g., Americans). Lastly, although public understanding of the scientific consensus is low, we find that conservatives and moderates are significantly less aware of the scientific consensus than liberals.

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Can Journalistic “False Balance” Distort Public Perception of Consensus in Expert Opinion?

Derek Koehler

Journal of Experimental Psychology: Applied, forthcoming

Abstract:
Media critics have expressed concern that journalistic “false balance” can distort the public’s perceptions of what ought to be noncontroversial subjects (e.g., climate change). I report several experiments testing the influence of presenting conflicting comments from 2 experts who disagree on an issue (balance condition) in addition to a complete count of the number of experts on a panel who favor either side. Compared with a control condition, who received only the complete count, participants in the balance condition gave ratings of the perceived agreement among the experts that did not discriminate as clearly between issues with and without strong expert consensus. Participants in the balance condition also perceived less agreement among the experts in general, and were less likely to think that there was enough agreement among experts on the high-consensus issues to guide government policy. Evidently, “false balance” can distort perceptions of expert opinion even when participants would seem to have all the information needed to correct for its influence.

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Rare disaster information can increase risk-taking

Ben Newell et al.

Nature Climate Change, February 2016, Pages 158–161

Abstract:
The recent increase in the frequency and impact of natural disasters highlights the need to provide the public with accurate information concerning disaster prevalence. Most approaches to this problem assume that providing summaries of the nature and scale of disasters will lead people to reduce their exposure to risk. Here we present experimental evidence that such ex post ‘news reports’ of disaster occurrences can increase the tolerance for risk-taking (which implies that rare events are underweighted). This result is robust across several hundred rounds of choices in a simulated microworld, persists even when the long-run expected value of risky choices is substantially lower than safe choices, and is contingent on providing risk information about disasters that have been (personally) experienced and those that have been avoided (‘forgone’ outcomes). The results suggest that augmenting personal experience with information summaries of the number of adverse events (for example, storms, floods) in different regions may, paradoxically, increase the appeal of a disaster-prone region. This finding implies a need to communicate long-term trends in severe climatic events, thereby reinforcing the accumulation of events, and the increase in their associated risks, across time.

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Help or hindrance? The travel, energy and carbon impacts of highly automated vehicles

Zia Wadud, Don MacKenzie & Paul Leiby

Transportation Research Part A: Policy and Practice, April 2016, Pages 1–18

Abstract:
Experts predict that new automobiles will be capable of driving themselves under limited conditions within 5–10 years, and under most conditions within 10–20 years. Automation may affect road vehicle energy consumption and greenhouse gas (GHG) emissions in a host of ways, positive and negative, by causing changes in travel demand, vehicle design, vehicle operating profiles, and choices of fuels. In this paper, we identify specific mechanisms through which automation may affect travel and energy demand and resulting GHG emissions and bring them together using a coherent energy decomposition framework. We review the literature for estimates of the energy impacts of each mechanism and, where the literature is lacking, develop our own estimates using engineering and economic analysis. We consider how widely applicable each mechanism is, and quantify the potential impact of each mechanism on a common basis: the percentage change it is expected to cause in total GHG emissions from light-duty or heavy-duty vehicles in the U.S. Our primary focus is travel related energy consumption and emissions, since potential lifecycle impacts are generally smaller in magnitude. We explore the net effects of automation on emissions through several illustrative scenarios, finding that automation might plausibly reduce road transport GHG emissions and energy use by nearly half – or nearly double them – depending on which effects come to dominate. We also find that many potential energy-reduction benefits may be realized through partial automation, while the major energy/emission downside risks appear more likely at full automation. We close by presenting some implications for policymakers and identifying priority areas for further research.

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Climate and health impacts of US emissions reductions consistent with 2 °C

Drew Shindell, Yunha Lee & Greg Faluvegi

Nature Climate Change, forthcoming

Abstract:
An emissions trajectory for the US consistent with 2 °C warming would require marked societal changes, making it crucial to understand the associated benefits. Previous studies have examined technological potentials and implementation costs and public health benefits have been quantified for less-aggressive potential emissions-reduction policies, but researchers have not yet fully explored the multiple benefits of reductions consistent with 2 °C. We examine the impacts of such highly ambitious scenarios for clean energy and vehicles. US transportation emissions reductions avoid ~0.03 °C global warming in 2030 (0.15 °C in 2100), whereas energy emissions reductions avoid ~0.05–0.07 °C 2030 warming (~0.25 °C in 2100). Nationally, however, clean energy policies produce climate disbenefits including warmer summers (although these would be eliminated by the remote effects of similar policies if they were undertaken elsewhere). The policies also greatly reduce damaging ambient particulate matter and ozone. By 2030, clean energy policies could prevent ~175,000 premature deaths, with ~22,000 (11,000–96,000; 95% confidence) fewer annually thereafter, whereas clean transportation could prevent ~120,000 premature deaths and ~14,000 (9,000–52,000) annually thereafter. Near-term national benefits are valued at ~US$250 billion (140 billion to 1,050 billion) per year, which is likely to exceed implementation costs. Including longer-term, worldwide climate impacts, benefits roughly quintuple, becoming ~5–10 times larger than estimated implementation costs. Achieving the benefits, however, would require both larger and broader emissions reductions than those in current legislation or regulations.

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Future temperature in southwest Asia projected to exceed a threshold for human adaptability

Jeremy Pal & Elfatih Eltahir

Nature Climate Change, February 2016, Pages 197–200

Abstract:
A human body may be able to adapt to extremes of dry-bulb temperature (commonly referred to as simply temperature) through perspiration and associated evaporative cooling provided that the wet-bulb temperature (a combined measure of temperature and humidity or degree of ‘mugginess’) remains below a threshold of 35 °C. This threshold defines a limit of survivability for a fit human under well-ventilated outdoor conditions and is lower for most people. We project using an ensemble of high-resolution regional climate model simulations that extremes of wet-bulb temperature in the region around the Arabian Gulf are likely to approach and exceed this critical threshold under the business-as-usual scenario of future greenhouse gas concentrations. Our results expose a specific regional hotspot where climate change, in the absence of significant mitigation, is likely to severely impact human habitability in the future.

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A decade of sea level rise slowed by climate-driven hydrology

J.T. Reager et al.

Science, 12 February 2016, Pages 699-703

Abstract:
Climate-driven changes in land water storage and their contributions to sea level rise have been absent from Intergovernmental Panel on Climate Change sea level budgets owing to observational challenges. Recent advances in satellite measurement of time-variable gravity combined with reconciled global glacier loss estimates enable a disaggregation of continental land mass changes and a quantification of this term. We found that between 2002 and 2014, climate variability resulted in an additional 3200 ± 900 gigatons of water being stored on land. This gain partially offset water losses from ice sheets, glaciers, and groundwater pumping, slowing the rate of sea level rise by 0.71 ± 0.20 millimeters per year. These findings highlight the importance of climate-driven changes in hydrology when assigning attribution to decadal changes in sea level.

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Temperature-driven global sea-level variability in the Common Era

Robert Kopp et al.

Proceedings of the National Academy of Sciences, forthcoming

Abstract:
We assess the relationship between temperature and global sea-level (GSL) variability over the Common Era through a statistical metaanalysis of proxy relative sea-level reconstructions and tide-gauge data. GSL rose at 0.1 ± 0.1 mm/y (2σ) over 0–700 CE. A GSL fall of 0.2 ± 0.2 mm/y over 1000–1400 CE is associated with ∼0.2 °C global mean cooling. A significant GSL acceleration began in the 19th century and yielded a 20th century rise that is extremely likely (probability P ≥ 0.95) faster than during any of the previous 27 centuries. A semiempirical model calibrated against the GSL reconstruction indicates that, in the absence of anthropogenic climate change, it is extremely likely (P = 0.95) that 20th century GSL would have risen by less than 51% of the observed 13.8 ± 1.5 cm. The new semiempirical model largely reconciles previous differences between semiempirical 21st century GSL projections and the process model-based projections summarized in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.

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European summer temperatures since Roman times

J. Luterbacher et al.

Environmental Research Letters, February 2016

Abstract:
The spatial context is critical when assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatio-temporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June–August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951–2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986–2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850–2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.

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Accelerated dryland expansion under climate change

Jianping Huang et al.

Nature Climate Change, February 2016, Pages 166–171

Abstract:
Drylands are home to more than 38% of the total global population and are one of the most sensitive areas to climate change and human activities. Projecting the areal change in drylands is essential for taking early action to prevent the aggravation of global desertification. However, dryland expansion has been underestimated in the Fifth Coupled Model Intercomparison Project (CMIP5) simulations considering the past 58 years (1948–2005). Here, using historical data to bias-correct CMIP5 projections, we show an increase in dryland expansion rate resulting in the drylands covering half of the global land surface by the end of this century. Dryland area, projected under representative concentration pathways (RCPs) RCP8.5 and RCP4.5, will increase by 23% and 11%, respectively, relative to 1961–1990 baseline, equalling 56% and 50%, respectively, of total land surface. Such an expansion of drylands would lead to reduced carbon sequestration and enhanced regional warming, resulting in warming trends over the present drylands that are double those over humid regions. The increasing aridity, enhanced warming and rapidly growing human population will exacerbate the risk of land degradation and desertification in the near future in the drylands of developing countries, where 78% of dryland expansion and 50% of the population growth will occur under RCP8.5.

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Dark Warming

Melissa Burt, David Randall & Mark Branson

Journal of Climate, January 2016, Pages 705–719

Abstract:
As the Arctic sea ice thins and ultimately disappears in a warming climate, its insulating power decreases. This causes the surface air temperature to approach the temperature of the relatively warm ocean water below the ice. The resulting increases in air temperature, water vapor, and cloudiness lead to an increase in the surface downwelling longwave radiation (DLR), which enables a further thinning of the ice. This positive ice–insulation feedback operates mainly in the autumn and winter. A climate change simulation with the Community Earth System Model shows that, averaged over the year, the increase in Arctic DLR is 3 times stronger than the increase in Arctic absorbed solar radiation at the surface. The warming of the surface air over the Arctic Ocean during fall and winter creates a strong thermal contrast with the colder surrounding continents. Sea level pressure falls over the Arctic Ocean, and the high-latitude circulation reorganizes into a shallow “winter monsoon.” The resulting increase in surface wind speed promotes stronger surface evaporation and higher humidity over portions of the Arctic Ocean, thus reinforcing the ice–insulation feedback.

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Climate Mechanism for Stronger Typhoons in a Warmer World

Nam-Young Kang & James Elsner

Journal of Climate, February 2016, Pages 1051–1057

Abstract:
Violent typhoons continue to have catastrophic impacts on economies and welfare, but how they are responding to global warming has yet to be fully understood. Here, an empirical framework is used to explain physically why observations support a tight connection between increasing ocean warmth and the increasing intensity of supertyphoons in the western North Pacific. It is shown that the energy needed for deep convection is on the rise with greater heat and moisture in the lower tropical troposphere but that this energy remains untapped when air pressure is high. Accordingly, tropical cyclone formation is becoming less common, but those that do form are likely to reach extreme intensities from the discharge of stored energy. These thermodynamic changes to the environment most significantly influence the upper portion of extreme typhoon intensities, indicating that supertyphoons are likely to be stronger at the expense of overall tropical cyclone occurrences in the western North Pacific.

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Future ocean hypercapnia driven by anthropogenic amplification of the natural CO2 cycle

Ben McNeil & Tristan Sasse

Nature, 21 January 2016, Pages 383–386

Abstract:
High carbon dioxide (CO2) concentrations in sea-water (ocean hypercapnia) can induce neurological, physiological and behavioural deficiencies in marine animals. Prediction of the onset and evolution of hypercapnia in the ocean requires a good understanding of annual variations in oceanic CO2 concentration, but there is a lack of relevant global observational data. Here we identify global ocean patterns of monthly variability in carbon concentration using observations that allow us to examine the evolution of surface-ocean CO2 levels over the entire annual cycle under increasing atmospheric CO2 concentrations. We predict that the present-day amplitude of the natural oscillations in oceanic CO2 concentration will be amplified by up to tenfold in some regions by 2100, if atmospheric CO2 concentrations continue to rise throughout this century (according to the RCP8.5 scenario of the Intergovernmental Panel on Climate Change). The findings from our data are broadly consistent with projections from Earth system climate models. Our predicted amplification of the annual CO2 cycle displays distinct global patterns that may expose major fisheries in the Southern, Pacific and North Atlantic oceans to hypercapnia many decades earlier than is expected from average atmospheric CO2 concentrations. We suggest that these ocean ‘CO2 hotspots’ evolve as a combination of the strong seasonal dynamics of CO2 concentration and the long-term effective storage of anthropogenic CO2 in the oceans that lowers the buffer capacity in these regions, causing a nonlinear amplification of CO2 concentration over the annual cycle. The onset of ocean hypercapnia (when the partial pressure of CO2 in sea-water exceeds 1,000 micro-atmospheres) is forecast for atmospheric CO2 concentrations that exceed 650 parts per million, with hypercapnia expected in up to half the surface ocean by 2100, assuming a high-emissions scenario (RCP8.5). Such extensive ocean hypercapnia has detrimental implications for fisheries during the twenty-first century.


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