Up the chimney

Kevin Lewis

December 21, 2017

Elite Domination of Public Doubts About Climate Change (Not Evolution)
Michael Tesler
Political Communication, forthcoming

This article examines the sources of ideological skepticism about two issues where there is a scientific consensus: climate change and evolution. The results indicate that self-identified conservatives doubt global warming in large part because of elite rhetoric, but that evolution beliefs are unrelated to reception of political discourse. News reception is perhaps the strongest predictor of conservatives’ climate change skepticism, but has no influence on their aversion to evolution. Moreover, the article leverages three sources of variation in elite discourse on climate change — temporal, cross-national, and experimental — to show that changes in the prevalence of ideological cues strongly affect public opinion about global warming. Politically attentive conservatives, in fact, were more likely to believe scientists about global warming than liberals were in the 1990s before the media depicted climate change as a partisan issue. The United States is also the only nation where political interest significantly predicts both conservatives’ skepticism about, and liberals’ belief in, climate change. Finally, evidence from a national survey experiment suggests that Americans would be less skeptical of manmade global warming if more Republicans in Congress believed in it, but a growing Congressional consensus about evolution would not diminish doubts about its existence.

The spatial distribution of Republican and Democratic climate opinions at state and local scales
Matto Mildenberger et al.
Climatic Change, December 2017, Pages 539–548

Even as US partisan polarization shapes climate and energy attitudes, substantial heterogeneity in climate opinions still exists among both Republicans and Democrats. To date, our understanding of this partisan heterogeneity has been limited to analysis of national- or, less commonly, state-level opinion poll subsamples. However, the dynamics of political representation and issue commitments play out over more finely resolved state and local scales. Here we use previously validated multilevel regression and post-stratification (MRP) models (Howe et al., Nat Clim Chang 5(6):596–603 2015; Mildenberger et al., PLoS One 11(8):e0159774 2016) combined with a novel approach to measuring the distribution of party members to model, for the first time, the spatial distribution of partisan climate and energy opinions. We find substantial geographic variation in Republican climate opinions across states and congressional districts. While Democratic party members consistently think human-caused global warming is happening and support climate policy reforms, the intensity of their climate beliefs also varies spatially at state and local scales. These results have policy-relevant implications for the trajectory of US climate policy reforms.

Disaster on the Horizon: The Price Effect of Sea Level Rise
Asaf Bernstein, Matthew Gustafson & Ryan Lewis
University of Colorado Working Paper, December 2017

Homes exposed to sea level rise (SLR) sell at a 7% discount relative to observably equivalent unexposed properties equidistant from the beach. This discount has grown over time and is driven by sophisticated buyers and communities worried about global warming. Consistent with causal identification of long horizon SLR costs, (1) we find no relation between SLR exposure and rental rates, (2) despite decreased remodeling among exposed homeowners, current SLR discounts are not caused by differential investment, (3) results hold controlling for flooded properties and views. Overall, we provide the first evidence on the price of SLR risk and its determinants. These findings contribute to the mixed literature on how investors price long-run risky cash flows and have implications for optimal climate change policy.

Attribution of extreme rainfall from Hurricane Harvey, August 2017
Geert Jan van Oldenborgh et al.
Environmental Research Letters, December 2017

During August 25–30, 2017, Hurricane Harvey stalled over Texas and caused extreme precipitation, particularly over Houston and the surrounding area on August 26–28. This resulted in extensive flooding with over 80 fatalities and large economic costs. It was an extremely rare event: the return period of the highest observed three-day precipitation amount, 1043.4 mm 3dy−1 at Baytown, is more than 9000 years (97.5% one-sided confidence interval) and return periods exceeded 1000 yr (750 mm 3dy−1) over a large area in the current climate. Observations since 1880 over the region show a clear positive trend in the intensity of extreme precipitation of between 12% and 22%, roughly two times the increase of the moisture holding capacity of the atmosphere expected for 1 °C warming according to the Clausius–Clapeyron (CC) relation. This would indicate that the moisture flux was increased by both the moisture content and stronger winds or updrafts driven by the heat of condensation of the moisture. We also analysed extreme rainfall in the Houston area in three ensembles of 25 km resolution models. The first also shows 2 × CC scaling, the second 1 × CC scaling and the third did not have a realistic representation of extreme rainfall on the Gulf Coast. Extrapolating these results to the 2017 event, we conclude that global warming made the precipitation about 15% (8%–19%) more intense, or equivalently made such an event three (1.5–5) times more likely. This analysis makes clear that extreme rainfall events along the Gulf Coast are on the rise. And while fortifying Houston to fully withstand the impact of an event as extreme as Hurricane Harvey may not be economically feasible, it is critical that information regarding the increasing risk of extreme rainfall events in general should be part of the discussion about future improvements to Houston's flood protection system.

The Marginal Product of Climate
Tatyana Deryugina & Solomon Hsiang
NBER Working Paper, November 2017

We develop an empirical approach to value changes to a climate in terms of total market output given optimal factor allocations in general equilibrium. Our approach accounts for unobservable heterogeneity across locations as well as the costs and benefits of adaptation in climates of arbitrary dimension. Importantly, we demonstrate that the Envelope Theorem implies the marginal product of a long-run climate can be exactly identified using only idiosyncratic weather variation. We apply this method to the temperature climate of the modern United States and find that, despite evidence that populations adapt, the marginal product of temperature has remained unchanged during 1970-2010, with high temperatures having low net value. Integrating marginal products recovers a value function for temperature, describing the causal effect of non-marginal climate changes net of adaptive re-optimization. We use this value function to consider the influence of temperature in the current cross-section and a future climate change scenario.

Regretful Decisions and Climate Change
Rebecca Livernois
Philosophy of the Social Sciences, forthcoming

Climate change has made pressing the question of why we do little to reduce greenhouse gas emissions. By analogy to the puzzle of the self-torturer, I argue that even if interpersonal and intergenerational conflicts of interest were resolved, we may still end up in a regretful environmental state when we aim to maximize our net benefit derived from polluting activities. This is because a rational agent with transitive preferences making climate change decisions faces incentives to over-pollute. This is caused by the presence of marginal costs that are uninformative of well-being in an uncertain and intertemporal decision problem.

Increased rainfall volume from future convective storms in the US
Andreas Prein et al.
Nature Climate Change, December 2017, Pages 880–884

Mesoscale convective system (MCS)-organized convective storms with a size of ~100 km have increased in frequency and intensity in the USA over the past 35 years, causing fatalities and economic losses. However, their poor representation in traditional climate models hampers the understanding of their change in the future. Here, a North American-scale convection-permitting model which is able to realistically simulate MSCs is used to investigate their change by the end-of-century under RCP8.5. A storm-tracking algorithm indicates that intense summertime MCS frequency will more than triple in North America. Furthermore, the combined effect of a 15–40% increase in maximum precipitation rates and a significant spreading of regions impacted by heavy precipitation results in up to 80% increases in the total MCS precipitation volume, focused in a 40 km radius around the storm centre. These typically neglected increases substantially raise future flood risk. Current investments in long-lived infrastructures, such as flood protection and water management systems, need to take these changes into account to improve climate-adaptation practices.

Human presence diminishes the importance of climate in driving fire activity across the United States
Alexandra Syphard et al.
Proceedings of the National Academy of Sciences, forthcoming

Growing human and ecological costs due to increasing wildfire are an urgent concern in policy and management, particularly given projections of worsening fire conditions under climate change. Thus, understanding the relationship between climatic variation and fire activity is a critically important scientific question. Different factors limit fire behavior in different places and times, but most fire-climate analyses are conducted across broad spatial extents that mask geographical variation. This could result in overly broad or inappropriate management and policy decisions that neglect to account for regionally specific or other important factors driving fire activity. We developed statistical models relating seasonal temperature and precipitation variables to historical annual fire activity for 37 different regions across the continental United States and asked whether and how fire-climate relationships vary geographically, and why climate is more important in some regions than in others. Climatic variation played a significant role in explaining annual fire activity in some regions, but the relative importance of seasonal temperature or precipitation, in addition to the overall importance of climate, varied substantially depending on geographical context. Human presence was the primary reason that climate explained less fire activity in some regions than in others. That is, where human presence was more prominent, climate was less important. This means that humans may not only influence fire regimes but their presence can actually override, or swamp out, the effect of climate. Thus, geographical context as well as human influence should be considered alongside climate in national wildfire policy and management.

Is There a Role for Human-Induced Climate Change in the Precipitation Decline that Drove the California Drought?
Richard Seager et al.
Journal of Climate, December 2017, Pages 10237–10258

The recent California drought was associated with a persistent ridge at the west coast of North America that has been associated with, in part, forcing from warm SST anomalies in the tropical west Pacific. Here it is considered whether there is a role for human-induced climate change in favoring such a west coast ridge. The models from phase 5 of the Coupled Model Intercomparison Project do not support such a case either in terms of a shift in the mean circulation or in variance that would favor increased intensity or frequency of ridges. The models also do not support shifts toward a drier mean climate or more frequent or intense dry winters or to tropical SST states that would favor west coast ridges. However, reanalyses do show that over the last century there has been a trend toward circulation anomalies over the Pacific–North American domain akin to those during the height of the California drought. The trend has been associated with a trend toward preferential warming of the Indo–west Pacific, an arrangement of tropical oceans and Pacific–North American circulation similar to that during winter 2013/14, the driest winter of the California drought. These height trends, however, are not reproduced in SST-forced atmosphere model ensembles. In contrast, idealized atmosphere modeling suggests that increased tropical Indo-Pacific zonal SST gradients are optimal for forcing height trends that favor a west coast ridge. These results allow a tenuous case for human-driven climate change driving increased gradients and favoring the west coast ridge, but observational data are not sufficiently accurate to confirm or reject this case.

The Curious Case of Projected Twenty-First-Century Drying but Greening in the American West
Justin Mankin et al.
Journal of Climate, November 2017, Pages 8689–8710

Climate models project significant twenty-first-century declines in water availability over the American West from anthropogenic warming. However, the physical mechanisms underpinning this response are poorly characterized, as are the uncertainties from vegetation’s modulation of evaporative losses. To understand the drivers and uncertainties of future hydroclimate in the American West, a 35-member single model ensemble is used to examine the response of summer soil moisture and runoff to anthropogenic forcing. Widespread dry season soil moisture declines occur across the region despite increases in total water-year precipitation and ubiquitous increases in plant water-use efficiency. These modeled soil moisture declines are initially forced by significant snowpack losses that directly diminish summer soil water, even in regions where water-year precipitation increases. When snowpack priming is coupled with a warming- and CO2-induced shift in phenology and increased primary production, widespread increases in leaf area further reduces summer soil moisture and runoff by outpacing decreased stomatal conductance from high CO2. The net effects lead to the co-occurrence of both a “greener” and “drier” future across the western United States. Because simulated vegetation exerts a large influence on predicted changes in water availability in the American West, these findings highlight the importance of reducing the substantial uncertainties in the ecological processes increasingly incorporated into numerical Earth system models.

High Resolution Dynamical Downscaling Ensemble Projections of Future Extreme Temperature Distributions for the United States
Zachary Zobel et al.
Earth's Future, forthcoming

The aim of this study is to examine projections of extreme temperatures over the continental United States (CONUS) for the 21st century using an ensemble of high spatial resolution dynamically downscaled model simulations with different boundary conditions. The downscaling uses the Weather Research and Forecast model at a spatial resolution of 12 km along with outputs from three different Coupled Model Intercomparison Project Phase 5 global climate models that provide boundary conditions under two different future greenhouse gas (GHG) concentration trajectories. The results from two decadal-length time slices (2045-2054 and 2085-2094) are compared with a historical decade (1995-2004). Probability density functions of daily maximum/minimum temperatures are analyzed over seven climatologically cohesive regions of the CONUS. The impacts of different boundary conditions as well as future GHG concentrations on extreme events such as heat waves and days with temperature higher than 95°F are also investigated. The results show that the intensity of extreme warm temperature in future summer is significantly increased, while the frequency of extreme cold temperature in future winter decreases. The distribution of summer daily maximum temperature experiences a significant warm-side shift and increased variability, while the distribution of winter daily minimum temperature is projected to have a less significant warm-side shift with decreased variability. Using “business-as-usual” scenario, 5-day heat waves are projected to occur at least 5-10 times per year in most CONUS and ≥95°F days will increase by 1-2 months by the end of the century.

Heat wave exposure in India in current, 1.5 °C, and 2.0 °C worlds
Vimal Mishra et al.
Environmental Research Letters, December 2017

Heatwaves with large impacts have increased in the recent past and will continue to increase under future warming. However, the implication for population exposure to severe heatwaves remains unexplored. Here, we characterize maximum potential human exposure (without passive/active reduction measures) to severe heatwaves in India. We show that if the global mean temperature is limited to 2.0 °C above pre-industrial conditions, the frequency of severe heatwaves will rise by 30 times the current climate by the end-21st century. In contrast, the frequency is projected to be about 2.5 times more (than the low-warming scenario of 2 °C) under conditions expected if the RCP8.5 'business-as-usual' emissions scenario is followed. Under the 2.0 °C low-warming target, population exposure to severe heatwaves is projected to increase by about 15 and 92 times the current level by the mid and end-21st century respectively. Strategies to reduce population growth in India during the 21st century may provide only limited mitigation of heatwave exposure mostly late in the century. Limiting global temperatures to 1.5 °C above preindustrial would reduce the exposure by half relative to RCP8.5 by the mid-21st century. If global temperatures are to exceed 1.5 °C then substantial measures will be required to offset the large increase in exposure to severe heatwaves in India.

Changes in the convective population and thermodynamic environments in convection-permitting regional climate simulations over the United States
Kristen Rasmussen et al.
Climate Dynamics, forthcoming

Novel high-resolution convection-permitting regional climate simulations over the US employing the pseudo-global warming approach are used to investigate changes in the convective population and thermodynamic environments in a future climate. Two continuous 13-year simulations were conducted using (1) ERA-Interim reanalysis and (2) ERA-Interim reanalysis plus a climate perturbation for the RCP8.5 scenario. The simulations adequately reproduce the observed precipitation diurnal cycle, indicating that they capture organized and propagating convection that most climate models cannot adequately represent. This study shows that weak to moderate convection will decrease and strong convection will increase in frequency in a future climate. Analysis of the thermodynamic environments supporting convection shows that both convective available potential energy (CAPE) and convective inhibition (CIN) increase downstream of the Rockies in a future climate. Previous studies suggest that CAPE will increase in a warming climate, however a corresponding increase in CIN acts as a balancing force to shift the convective population by suppressing weak to moderate convection and provides an environment where CAPE can build to extreme levels that may result in more frequent severe convection. An idealized investigation of fundamental changes in the thermodynamic environment was conducted by shifting a standard atmospheric profile by ± 5 °C. When temperature is increased, both CAPE and CIN increase in magnitude, while the opposite is true for decreased temperatures. Thus, even in the absence of synoptic and mesoscale variations, a warmer climate will provide more CAPE and CIN that will shift the convective population, likely impacting water and energy budgets on Earth.

The Impact of Climate Change on Hazardous Convective Weather in the United States: Insight from High-Resolution Dynamical Downscaling
Kimberly Hoogewind, Michael Baldwin & Robert Trapp
Journal of Climate, December 2017, Pages 10081–10100

This study explores the potential impact anthropogenic climate change may have upon hazardous convective weather (HCW; i.e., tornadoes, large hail, and damaging wind gusts) in the United States. Utilizing the Weather Research and Forecasting (WRF) Model, high-resolution (4 km) dynamically downscaled simulations of the Geophysical Fluid Dynamics Laboratory Climate Model, version 3 (GFDL CM3), are produced for a historical (1971–2000) and future (2071–2100) period. Synthetic HCW day climatologies are created using upward vertical velocity (UVV) exceeding 22 m s−1 as a proxy for HCW occurrence and subsequently compared to the environmental approach of estimating changes in daily frequency of convective environments favorable for HCW (NDSEV) from the driving climate model. Results from the WRF simulations demonstrate that the proxy for HCW becomes more frequent by the end of the twenty-first century, with the greatest absolute increases in daily frequency occurring during the spring and summer. Compared to NDSEV from GFDL CM3, both approaches suggest a longer HCW season, perhaps lengthening by more than a month. The change in environmental estimates are 2–4 times larger than that gauged from WRF; further analyses show that the conditional probability of HCW given NDSEV declines during summer for much of the central United States, a result that may be attributed to both an increase in the magnitude of convective inhibition (CIN) and decreased forcing for ascent, hindering convective initiation. Such an outcome supports the motivation for continued use of dynamical downscaling to overcome the limitations of the GCM-based environmental analysis.

Effectiveness of state climate and energy policies in reducing power-sector CO2 emissions
Geoff Martin & Eri Saikawa
Nature Climate Change, December 2017, Pages 912–919

States have historically been the primary drivers of climate change policy in the US, particularly with regard to emissions from power plants. States have implemented policies designed either to directly curb greenhouse gas (GHG) emissions from power plants, or to encourage energy efficiency and renewable energy growth. With the federal government withdrawing from the global climate agreement, understanding which state-level policies have successfully mitigated power-plant emissions is urgent. Past research has assessed policy effectiveness using data for periods before the adoption of many policies. We assess 17 policies using the latest data on state-level power-sector CO2 emissions. We find that policies with mandatory compliance are reducing power-plant emissions, while voluntary policies are not. Electric decoupling, mandatory GHG registry/reporting and public benefit funds are associated with the largest reduction in emissions. Mandatory GHG registry/reporting and public benefit funds are also associated with a large reduction in emissions intensity.

Beliefs about Climate Beliefs: The Importance of Second-Order Opinions for Climate Politics
Matto Mildenberger & Dustin Tingley
British Journal of Political Science, forthcoming

When political action entails individual costs but group-contingent benefits, political participation may depend on an individual’s perceptions of others’ beliefs; yet detailed empirical attention to these second-order beliefs – beliefs about the beliefs of others – remains rare. We offer the first comprehensive examination of the distribution and content of second-order climate beliefs in the United States and China, drawing from six new opinion surveys of mass publics, political elites and intellectual elites. We demonstrate that all classes of political actors have second-order beliefs characterized by egocentric bias and global underestimation of pro-climate positions. We then demonstrate experimentally that individual support for pro-climate policies increases after respondents update their second-order beliefs. We conclude that scholars should focus more closely on second-order beliefs as a key factor shaping climate policy inaction and that scholars can use the climate case to extend their understanding of second-order beliefs more broadly.

Near-Future Prediction of Tropical Cyclone Activity over the North Atlantic
Woosuk Choi et al.
Journal of Climate, November 2017, Pages 8795–8809

Prediction of tropical cyclone (TC) activity is essential to better prepare for and mitigate TC-induced disasters. Although many studies have attempted to predict TC activity on various time scales, very few have focused on near-future predictions. Here a decrease in seasonal TC activity over the North Atlantic (NA) for 2016–30 is shown using a track-pattern-based TC prediction model. The TC model is forced by long-term coupled simulations initialized using reanalysis data. Unfavorable conditions for TC development including strengthened vertical wind shear, enhanced low-level anticyclonic flow, and cooled sea surface temperature (SST) over the tropical NA are found in the simulations. Most of the environmental changes are attributable to cooling of the NA basinwide SST (NASST) and more frequent El Niño episodes in the near future. The consistent NASST warming trend in the projections from phase 5 of the Coupled Model Intercomparison Project (CMIP5) suggests that natural variability is more dominant than anthropogenic forcing over the NA in the near-future period.

Greater future global warming inferred from Earth’s recent energy budget
Patrick Brown & Ken Caldeira
Nature, 7 December 2017, Pages 45–50

Climate models provide the principal means of projecting global warming over the remainder of the twenty-first century but modelled estimates of warming vary by a factor of approximately two even under the same radiative forcing scenarios. Across-model relationships between currently observable attributes of the climate system and the simulated magnitude of future warming have the potential to inform projections. Here we show that robust across-model relationships exist between the global spatial patterns of several fundamental attributes of Earth’s top-of-atmosphere energy budget and the magnitude of projected global warming. When we constrain the model projections with observations, we obtain greater means and narrower ranges of future global warming across the major radiative forcing scenarios, in general. In particular, we find that the observationally informed warming projection for the end of the twenty-first century for the steepest radiative forcing scenario is about 15 per cent warmer (+0.5 degrees Celsius) with a reduction of about a third in the two-standard-deviation spread (−1.2 degrees Celsius) relative to the raw model projections reported by the Intergovernmental Panel on Climate Change. Our results suggest that achieving any given global temperature stabilization target will require steeper greenhouse gas emissions reductions than previously calculated.

Southward shift of the global wind energy resource under high carbon dioxide emissions
Kristopher Karnauskas, Julie Lundquist & Lei Zhang
Nature Geoscience, forthcoming

The use of wind energy resource is an integral part of many nations’ strategies towards realizing the carbon emissions reduction targets set forth in the Paris Agreement, and global installed wind power cumulative capacity has grown on average by 22% per year since 2006. However, assessments of wind energy resource are usually based on today’s climate, rather than taking into account that anthropogenic greenhouse gas emissions continue to modify the global atmospheric circulation. Here, we apply an industry wind turbine power curve to simulations of high and low future emissions scenarios in an ensemble of ten fully coupled global climate models to investigate large-scale changes in wind power across the globe. Our calculations reveal decreases in wind power across the Northern Hemisphere mid-latitudes and increases across the tropics and Southern Hemisphere, with substantial regional variations. The changes across the northern mid-latitudes are robust responses over time in both emissions scenarios, whereas the Southern Hemisphere changes appear critically sensitive to each individual emissions scenario. In addition, we find that established features of climate change can explain these patterns: polar amplification is implicated in the northern mid-latitude decrease in wind power, and enhanced land–sea thermal gradients account for the tropical and southern subtropical increases.

Groundwater Depletion: A Significant Unreported Source of Atmospheric Carbon Dioxide
Warren Wood & David Hyndman
Earth's Future, November 2017, Pages 1133–1135

Quantifying the annual flux of CO2 (carbon dioxide) and equivalent emissions to the atmosphere is critical for both policy decisions and modeling of future climate change. Given the importance of greenhouse gas emissions to climate change and a recognized mismatch between sources and sinks (e.g., Liu & Dreybrodt, 2015), it is important to quantify these parameters. A significant and previously unrecognized CO2 contribution arises from groundwater depletion (net removal from storage). The average annual 1.7 MMT (million metric tons) CO2 released in the United States from this source is greater than approximately one third of the 23 major sources reported by the US EPA (United States Environmental Protection Agency) to the IPCC (Intergovernmental Panel on Climate Change; US EPA, 2016).

Recently amplified arctic warming has contributed to a continual global warming trend
Jianbin Huang et al.
Nature Climate Change, December 2017, Pages 875–879

The existence and magnitude of the recently suggested global warming hiatus, or slowdown, have been strongly debated. Although various physical processes have been examined to elucidate this phenomenon, the accuracy and completeness of observational data that comprise global average surface air temperature (SAT) datasets is a concern. In particular, these datasets lack either complete geographic coverage or in situ observations over the Arctic, owing to the sparse observational network in this area. As a consequence, the contribution of Arctic warming to global SAT changes may have been underestimated, leading to an uncertainty in the hiatus debate. Here, we constructed a new Arctic SAT dataset using the most recently updated global SATs and a drifting buoys based Arctic SAT dataset through employing the ‘data interpolating empirical orthogonal functions’ method. Our estimate of global SAT rate of increase is around 0.112 °C per decade, instead of 0.05 °C per decade from IPCC AR51, for 1998–2012. Analysis of this dataset shows that the amplified Arctic warming over the past decade has significantly contributed to a continual global warming trend, rather than a hiatus or slowdown.

Evolving Understanding of Antarctic Ice-Sheet Physics and Ambiguity in Probabilistic Sea-Level Projections
Robert Kopp et al.
Earth's Future, forthcoming

Mechanisms such as ice-shelf hydrofracturing and ice-cliff collapse may rapidly increase discharge from marine-based ice sheets. Here, we link a probabilistic framework for sea-level projections to a small ensemble of Antarctic ice-sheet (AIS) simulations incorporating these physical processes to explore their influence on global-mean sea-level (GMSL) and relative sea-level (RSL). We compare the new projections to past results using expert assessment and structured expert elicitation about AIS changes. Under high greenhouse gas emissions (Representative Concentration Pathway [RCP] 8.5), median projected 21st century GMSL rise increases from 79 to 146 cm. Without protective measures, revised median RSL projections would by 2100 submerge land currently home to 153 million people, an increase of 44 million. The use of a physical model, rather than simple parameterizations assuming constant acceleration of ice loss, increases forcing sensitivity: overlap between the central 90% of simulations for 2100 for RCP 8.5 (93–243 cm) and RCP 2.6 (26–98 cm) is minimal. By 2300, the gap between median GMSL estimates for RCP 8.5 and RCP 2.6 reaches >10 m, with median RSL projections for RCP 8.5 jeopardizing land now occupied by 950 million people (versus 167 million for RCP 2.6). The minimal correlation between the contribution of AIS to GMSL by 2050 and that in 2100 and beyond implies current sea-level observations cannot exclude future extreme outcomes. The sensitivity of post-2050 projections to deeply uncertain physics highlights the need for robust decision and adaptive management frameworks.

Deep oceans may acidify faster than anticipated due to global warming
Chen-Tung Arthur Chen et al.
Nature Climate Change, December 2017, Pages 890–894

Oceans worldwide are undergoing acidification due to the penetration of anthropogenic CO2 from the atmosphere. The rate of acidification generally diminishes with increasing depth. Yet, slowing down of the thermohaline circulation due to global warming could reduce the pH in the deep oceans, as more organic material would decompose with a longer residence time. To elucidate this process, a time-series study at a climatically sensitive region with sufficient duration and resolution is needed. Here we show that deep waters in the Sea of Japan are undergoing reduced ventilation, reducing the pH of seawater. As a result, the acidification rate near the bottom of the Sea of Japan is 27% higher than the rate at the surface, which is the same as that predicted assuming an air–sea CO2 equilibrium. This reduced ventilation may be due to global warming and, as an oceanic microcosm with its own deep- and bottom-water formations, the Sea of Japan provides an insight into how future warming might alter the deep-ocean acidification. 

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