Scorched-earth policy
The Supply of Environmentalism
Edward Glaeser
NBER Working Paper, August 2013
Abstract:
Long before economics turned to psychology, environmentalists were nudging and framing and pushing their cause like highly gifted amateur psychologists. Their interventions seem to have changed behavior by altering beliefs, norms and preferences, but because psychological interventions are often coarse, inadvertent, offsetting side effects occur. After discussing the interplay between environmental preference-making and economics, I turn to three areas where strong, simple views have spread — electric cars, recycling and local conservation efforts. In all three areas, environmental rules of thumb can lead to significant, adverse environmental side effects. Local environmentalism, for example, may increase carbon emissions by pushing development from low emission areas, like coastal California, to high emissions areas elsewhere. I end by discussing how economic analysis of the political market for ideas can make sense of the remarkable disparity of views on global warming.
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Quantifying the Influence of Climate on Human Conflict
Solomon Hsiang, Marshall Burke & Edward Miguel
Science, forthcoming
Abstract:
A rapidly growing body of research examines whether human conflict can be affected by climatic changes. Drawing from archaeology, criminology, economics, geography, history, political science, and psychology, we assemble and analyze the 60 most rigorous quantitative studies and document, for the first time, a remarkable convergence of results. We find strong causal evidence linking climatic events to human conflict across a range of spatial and temporal scales and across all major regions of the world. The magnitude of climate's influence is substantial: for each 1 standard deviation (1σ) change in climate toward warmer temperatures or more extreme rainfall, median estimates indicate that the frequency of interpersonal violence rises 4% and the frequency of intergroup conflict rises 14%. Because locations throughout the inhabited world are expected to warm 2 to 4σ by 2050, amplified rates of human conflict could represent a large and critical impact of anthropogenic climate change.
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Carbon Taxes vs. Cap and Trade: A Critical Review
Lawrence Goulder & Andrew Schein
NBER Working Paper, August 2013
Abstract:
We examine the relative attractions of a carbon tax, a “pure” cap-and-trade system, and a “hybrid” option (a cap-and-trade system with a price ceiling and/or price floor). We show that the various options are equivalent along more dimensions than often are recognized. In addition, we bring out important dimensions along which the approaches have very different impacts. Several of these dimensions have received little attention in prior literature. A key finding is that exogenous emissions pricing (whether through a carbon tax or through the hybrid option) has a number of attractions over pure cap and trade. Beyond helping prevent price volatility and reducing expected policy errors in the face of uncertainties, exogenous pricing helps avoid problematic interactions with other climate policies and helps avoid large wealth transfers to oil exporting countries.
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Future flood losses in major coastal cities
Stephane Hallegatte et al.
Nature Climate Change, September 2013, Pages 802-806
Abstract:
Flood exposure is increasing in coastal cities owing to growing populations and assets, the changing climate, and subsidence. Here we provide a quantification of present and future flood losses in the 136 largest coastal cities. Using a new database of urban protection and different assumptions on adaptation, we account for existing and future flood defences. Average global flood losses in 2005 are estimated to be approximately US$6 billion per year, increasing to US$52 billion by 2050 with projected socio-economic change alone. With climate change and subsidence, present protection will need to be upgraded to avoid unacceptable losses of US$1 trillion or more per year. Even if adaptation investments maintain constant flood probability, subsidence and sea-level rise will increase global flood losses to US$60–63 billion per year in 2050. To maintain present flood risk, adaptation will need to reduce flood probabilities below present values. In this case, the magnitude of losses when floods do occur would increase, often by more than 50%, making it critical to also prepare for larger disasters than we experience today. The analysis identifies the cities that seem most vulnerable to these trends, that is, where the largest increase in losses can be expected.
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The Effect of the Kyoto Protocol on Carbon Emissions
Rahel Aichele & Gabriel Felbermayr
Journal of Policy Analysis and Management, forthcoming
Abstract:
Since 1997, CO2 emissions have continued to rise in many countries despite their emission caps under the Kyoto Protocol (Kyoto). Failure to meet promised targets, however, does not imply that Kyoto has been pointless. Whether Kyoto has made a difference relative to the counterfactual of “No Kyoto” is an empirical question that requires an instrumental variables strategy. We argue that countries’ ratification of the statutes governing the International Criminal Court is a valid instrument for ratification of Kyoto commitments. In our panel fixed effects estimations, the instrument easily passes weak identification and overidentification tests. It can be plausibly excluded from our second-stage equations and does not cause CO2 emissions. Our estimates suggest that Kyoto ratification has a quantitatively large (about 10 percent) and robust, though only moderately statistically significant, negative effect on CO2 emissions. We also show that higher fuel prices and a different energy mix in Kyoto countries support this result.
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The social cost of CO2 in a low-growth world
Chris Hope & Mat Hope
Nature Climate Change, August 2013, Pages 722–724
Abstract:
Action on mitigating climate change seems to be grinding to a halt within the global political arena. Major emitters seem unwilling to accept binding emissions reductions targets as their economies have stagnated. The talks at the United Nations Framework Convention on Climate Change conference in Copenhagen in 2009 were meant to represent a watershed moment for global cooperation on climate change but produced little more than a symbolic accord. Fast forward another three years and the outcomes of the Doha negotiations deferred the key decisions on climate change mitigation to 2015, as the Durban Platform did before. Is this neglect justified? Here we use the PAGE09 integrated assessment model to estimate the mean social cost of CO2 for a wide range of economic growth scenarios. The social cost of CO2 measures the net present value of the extra damage caused by the emission of one more tonne of CO2 today. The results show that in a world with sustained lower economic growth the mean social cost of CO2 increases because the climate impacts occur in a relatively poor world, suggesting that, if anything, mitigating climate change should be a higher priority for policymakers in a low-growth world.
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Long-Term Climate Change Commitment and Reversibility: An EMIC Intercomparison
Kirsten Zickfeld et al.
Journal of Climate, August 2013, Pages 5782–5809
Abstract:
This paper summarizes the results of an intercomparison project with Earth System Models of Intermediate Complexity (EMICs) undertaken in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). The focus is on long-term climate projections designed to 1) quantify the climate change commitment of different radiative forcing trajectories and 2) explore the extent to which climate change is reversible on human time scales. All commitment simulations follow the four representative concentration pathways (RCPs) and their extensions to year 2300. Most EMICs simulate substantial surface air temperature and thermosteric sea level rise commitment following stabilization of the atmospheric composition at year-2300 levels. The meridional overturning circulation (MOC) is weakened temporarily and recovers to near-preindustrial values in most models for RCPs 2.6–6.0. The MOC weakening is more persistent for RCP8.5. Elimination of anthropogenic CO2 emissions after 2300 results in slowly decreasing atmospheric CO2 concentrations. At year 3000 atmospheric CO2 is still at more than half its year-2300 level in all EMICs for RCPs 4.5–8.5. Surface air temperature remains constant or decreases slightly and thermosteric sea level rise continues for centuries after elimination of CO2 emissions in all EMICs. Restoration of atmospheric CO2 from RCP to preindustrial levels over 100–1000 years requires large artificial removal of CO2 from the atmosphere and does not result in the simultaneous return to preindustrial climate conditions, as surface air temperature and sea level response exhibit a substantial time lag relative to atmospheric CO2.
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Time-dependent climate sensitivity and the legacy of anthropogenic greenhouse gas emissions
Richard Zeebe
Proceedings of the National Academy of Sciences, 20 August 2013, Pages 13739-13744
Abstract:
Climate sensitivity measures the response of Earth’s surface temperature to changes in forcing. The response depends on various climate processes that feed back on the initial forcing on different timescales. Understanding climate sensitivity is fundamental to reconstructing Earth’s climatic history as well as predicting future climate change. On timescales shorter than centuries, only fast climate feedbacks including water vapor, lapse rate, clouds, and snow/sea ice albedo are usually considered. However, on timescales longer than millennia, the generally higher Earth system sensitivity becomes relevant, including changes in ice sheets, vegetation, ocean circulation, biogeochemical cycling, etc. Here, I introduce the time-dependent climate sensitivity, which unifies fast-feedback and Earth system sensitivity. I show that warming projections, which include a time-dependent climate sensitivity, exhibit an enhanced feedback between surface warming and ocean CO2 solubility, which in turn leads to higher atmospheric CO2 levels and further warming. Compared with earlier studies, my results predict a much longer lifetime of human-induced future warming (23,000–165,000 y), which increases the likelihood of large ice sheet melting and major sea level rise. The main point regarding the legacy of anthropogenic greenhouse gas emissions is that, even if the fast-feedback sensitivity is no more than 3 K per CO2 doubling, there will likely be additional long-term warming from slow climate feedbacks. Time-dependent climate sensitivity also helps explaining intense and prolonged warming in response to massive carbon release as documented for past events such as the Paleocene–Eocene Thermal Maximum.
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Global flood risk under climate change
Yukiko Hirabayashi et al.
Nature Climate Change, September 2013, Pages 816–821
Abstract:
A warmer climate would increase the risk of floods. So far, only a few studies have projected changes in floods on a global scale. None of these studies relied on multiple climate models. A few global studies have started to estimate the exposure to flooding (population in potential inundation areas) as a proxy of risk, but none of them has estimated it in a warmer future climate. Here we present global flood risk for the end of this century based on the outputs of 11 climate models. A state-of-the-art global river routing model with an inundation scheme was employed to compute river discharge and inundation area. An ensemble of projections under a new high-concentration scenario demonstrates a large increase in flood frequency in Southeast Asia, Peninsular India, eastern Africa and the northern half of the Andes, with small uncertainty in the direction of change. In certain areas of the world, however, flood frequency is projected to decrease. Another larger ensemble of projections under four new concentration scenarios reveals that the global exposure to floods would increase depending on the degree of warming, but interannual variability of the exposure may imply the necessity of adaptation before significant warming.
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Jeffrey Wilson et al.
Energy Policy, forthcoming
Abstract:
This research investigates whether where we live matters in terms of contributions to direct greenhouse gas (GHG) emissions. Using results from the Halifax Space Time Activity Research (STAR) project, we estimate GHG emissions for 1920 randomly selected respondents in Halifax Regional Municipality, Nova Scotia, Canada. The unique data set allows us to report direct GHG emissions with an unprecedented level of specificity at the sub-regional scale using household energy-use survey data and GPS-verified travel data. We report results and investigate statistical differences between communities and urban–rural zones (inner city, suburban, and inner and outer commuter belts). Results reveal considerable spatial variability in direct GHG emissions across the study area. Our findings indicate that individuals living in the suburbs generate similar amounts of GHG emissions (20.5 kg CO2e person−1 day−1) to those living in the inner city (20.2 kg CO2e person−1 day−1), challenging a widely held assumption that living in the urban centre is better for sustainability. However, individuals in more rural areas have significantly higher transport-related GHG emissions than those living in the inner city and suburbs. Our results underscore the importance of understanding the spatial distribution of GHG emissions at the sub-regional scale.
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Low simulated radiation limit for runaway greenhouse climates
Colin Goldblatt et al.
Nature Geoscience, August 2013, Pages 661–667
Abstract:
The atmospheres of terrestrial planets are expected to be in long-term radiation balance: an increase in the absorption of solar radiation warms the surface and troposphere, which leads to a matching increase in the emission of thermal radiation. Warming a wet planet such as Earth would make the atmosphere moist and optically thick such that only thermal radiation emitted from the upper troposphere can escape to space. Hence, for a hot moist atmosphere, there is an upper limit on the thermal emission that is unrelated to surface temperature. If the solar radiation absorbed exceeds this limit, the planet will heat uncontrollably and the entire ocean will evaporate — the so-called runaway greenhouse. Here we model the solar and thermal radiative transfer in incipient and complete runaway greenhouse atmospheres at line-by-line spectral resolution using a modern spectral database. We find a thermal radiation limit of 282 W m−2 (lower than previously reported) and that 294 W m−2 of solar radiation is absorbed (higher than previously reported). Therefore, a steam atmosphere induced by such a runaway greenhouse may be a stable state for a planet receiving a similar amount of solar radiation as Earth today. Avoiding a runaway greenhouse on Earth requires that the atmosphere is subsaturated with water, and that the albedo effect of clouds exceeds their greenhouse effect. A runaway greenhouse could in theory be triggered by increased greenhouse forcing, but anthropogenic emissions are probably insufficient.
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Historic and future increase in the global land area affected by monthly heat extremes
Dim Coumou & Alexander Robinson
Environmental Research Letters, August 2013
Abstract:
Climatic warming of about 0.5 ° C in the global mean since the 1970s has strongly increased the occurrence-probability of heat extremes on monthly to seasonal time scales. For the 21st century, climate models predict more substantial warming. Here we show that the multi-model mean of the CMIP5 (Coupled Model Intercomparison Project) climate models accurately reproduces the evolution over time and spatial patterns of the historically observed increase in monthly heat extremes. For the near-term (i.e., by 2040), the models predict a robust, several-fold increase in the frequency of such heat extremes, irrespective of the emission scenario. However, mitigation can strongly reduce the number of heat extremes by the second half of the 21st century. Unmitigated climate change causes most (>50%) continental regions to move to a new climatic regime with the coldest summer months by the end of the century substantially hotter than the hottest experienced today. We show that the land fraction experiencing extreme heat as a function of global mean temperature follows a simple cumulative distribution function, which depends only on natural variability and the level of spatial heterogeneity in the warming.
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Richard Brusca et al.
Ecology and Evolution, forthcoming
Abstract:
Models analyzing how Southwestern plant communities will respond to climate change predict that increases in temperature will lead to upward elevational shifts of montane species. We tested this hypothesis by reexamining Robert Whittaker's 1963 plant transect in the Santa Catalina Mountains of southern Arizona, finding that this process is already well underway. Our survey, five decades after Whittaker's, reveals large changes in the elevational ranges of common montane plants, while mean annual rainfall has decreased over the past 20 years, and mean annual temperatures increased 0.25°C/decade from 1949 to 2011 in the Tucson Basin. Although elevational changes in species are individualistic, significant overall upward movement of the lower elevation boundaries, and elevational range contractions, have occurred. This is the first documentation of significant upward shifts of lower elevation range boundaries in Southwestern montane plant species over decadal time, confirming that previous hypotheses are correct in their prediction that mountain communities in the Southwest will be strongly impacted by warming, and that the Southwest is already experiencing a rapid vegetation change.
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Projections of seasonal patterns in temperature-related deaths for Manhattan, New York
Tiantian Li, Radley Horton & Patrick Kinney
Nature Climate Change, August 2013, Pages 717–721
Abstract:
Global average temperatures have been rising for the past half-century, and the warming trend has accelerated in recent decades. Further warming is expected over the next few decades, with significant regional variations. These warming trends will probably result in more frequent, intense and persistent periods of hot temperatures in summer, and generally higher temperatures in winter. Daily death counts in cities increase markedly when temperatures reach levels that are very high relative to what is normal in a given location. Relatively cold temperatures also seem to carry risk. Rising temperatures may result in more heat-related mortality but may also reduce cold-related mortality, and the net impact on annual mortality remains uncertain. Here we use 16 downscaled global climate models and two emissions scenarios to estimate present and future seasonal patterns in temperature-related mortality in Manhattan, New York. All 32 projections yielded warm-season increases and cold-season decreases in temperature-related mortality, with positive net annual temperature-related deaths in all cases. Monthly analyses showed that the largest percentage increases may occur in May and September. These results suggest that, over a range of models and scenarios of future greenhouse gas emissions, increases in heat-related mortality could outweigh reductions in cold-related mortality, with shifting seasonal patterns.
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A method for estimating the cost to sequester carbon dioxide by delivering iron to the ocean
Daniel Harrison
International Journal of Global Warming, Summer 2013, Pages 231 - 254
Abstract:
The need to find economical methods of CO2 sequestration is now urgent. Ocean iron fertilisation has been suggested as a low cost mitigation option to capture and store carbon. However, previous methods of estimating the cost fail to account for many of the losses and offsets occurring over the storage period. A method for calculating the net carbon stored from iron fertilisation of high nutrient low chlorophyll ocean regions is provided. Ship based fertilisation of the Southern Ocean is considered as a case study, on average, a single fertilisation is found to result in a net sequestration of 0.01 t C km−2 for 100 years at a cost of US$457 per tonne CO2. Previous estimates of cost underestimate the economic challenge of distributing low concentrations of iron over large areas of the ocean surface, and the subsequent loss processes that result in only a small net storage of carbon per km2 fertilised. Technologies that could lower the cost are discussed.
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Thomas Knutson et al.
Journal of Climate, September 2013, Pages 6591–6617
Abstract:
Twenty-first-century projections of Atlantic climate change are downscaled to explore the robustness of potential changes in hurricane activity. Multimodel ensembles using the phase 3 of the Coupled Model Intercomparison Project (CMIP3)/Special Report on Emissions Scenarios A1B (SRES A1B; late-twenty-first century) and phase 5 of the Coupled Model Intercomparison Project (CMIP5)/representative concentration pathway 4.5 (RCP4.5; early- and late-twenty-first century) scenarios are examined. Ten individual CMIP3 models are downscaled to assess the spread of results among the CMIP3 (but not the CMIP5) models. Downscaling simulations are compared for 18-km grid regional and 50-km grid global models. Storm cases from the regional model are further downscaled into the Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model (9-km inner grid spacing, with ocean coupling) to simulate intense hurricanes at a finer resolution. A significant reduction in tropical storm frequency is projected for the CMIP3 (−27%), CMIP5-early (−20%) and CMIP5-late (−23%) ensembles and for 5 of the 10 individual CMIP3 models. Lifetime maximum hurricane intensity increases significantly in the high-resolution experiments—by 4%–6% for CMIP3 and CMIP5 ensembles. A significant increase (+87%) in the frequency of very intense (categories 4 and 5) hurricanes (winds ≥ 59 m s−1) is projected using CMIP3, but smaller, only marginally significant increases are projected (+45% and +39%) for the CMIP5-early and CMIP5-late scenarios. Hurricane rainfall rates increase robustly for the CMIP3 and CMIP5 scenarios. For the late-twenty-first century, this increase amounts to +20% to +30% in the model hurricane’s inner core, with a smaller increase (~10%) for averaging radii of 200 km or larger. The fractional increase in precipitation at large radii (200–400 km) approximates that expected from environmental water vapor content scaling, while increases for the inner core exceed this level.
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Arctic warming and your weather: Public belief in the connection
Lawrence Hamilton & Mary Lemcke-Stampone
International Journal of Climatology, forthcoming
Abstract:
Will Arctic warming affect mid-latitude weather? Many researchers think so, and have addressed this question through scientific articles and news media. Much of the public accepts such a connection as well. Across three New Hampshire surveys with more than 1500 interviews, 60% of respondents say they think future Arctic warming would have major effects on their weather. Arctic/weather responses changed little after Superstorm Sandy brushed the region, but exhibit consistently strong partisan divisions that grow wider with education. Belief in an Arctic/weather connection also varies, in a nonlinear pattern, with the temperature anomaly around day of interview. Interviewed on unseasonably warm or cool days, respondents are more likely to think that Arctic warming would have major effects on their weather. This unscientific response seems to mirror the scientific discussion about extremes.
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Near-term climate mitigation by short-lived forcers
Steven Smith & Andrew Mizrahi
Proceedings of the National Academy of Sciences, 27 August 2013, Pages 14202-14206
Abstract:
Emissions reductions focused on anthropogenic climate-forcing agents with relatively short atmospheric lifetimes, such as methane (CH4) and black carbon, have been suggested as a strategy to reduce the rate of climate change over the next several decades. We find that reductions of methane and black carbon would likely have only a modest impact on near-term global climate warming. Even with maximally feasible reductions phased in from 2015 to 2035, global mean temperatures in 2050 would be reduced by 0.16 °C, with a range of 0.04–0.35 °C because of uncertainties in carbonaceous aerosol emissions and aerosol forcing per unit of emissions. The high end of this range is only possible if total historical aerosol forcing is relatively small. More realistic emission reductions would likely provide an even smaller climate benefit. We find that the climate benefit from reductions in short-lived forcing agents are smaller than previously estimated. These near-term climate benefits of targeted reductions in short-lived forcers are not substantially different in magnitude from the benefits from a comprehensive climate policy.
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Global warming amplified by reduced sulphur fluxes as a result of ocean acidification
Katharina Six et al.
Nature Climate Change, forthcoming
Abstract:
Climate change and decreasing seawater pH (ocean acidification) have widely been considered as uncoupled consequences of the anthropogenic CO2 perturbation. Recently, experiments in seawater enclosures (mesocosms) showed that concentrations of dimethylsulphide (DMS), a biogenic sulphur compound, were markedly lower in a low-pH environment. Marine DMS emissions are the largest natural source of atmospheric sulphur and changes in their strength have the potential to alter the Earth’s radiation budget. Here we establish observational-based relationships between pH changes and DMS concentrations to estimate changes in future DMS emissions with Earth system model climate simulations. Global DMS emissions decrease by about 18(±3)% in 2100 compared with pre-industrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS emissions induce a significant additional radiative forcing, of which 83% is attributed to the impact of ocean acidification, tantamount to an equilibrium temperature response between 0.23 and 0.48 K. Our results indicate that ocean acidification has the potential to exacerbate anthropogenic warming through a mechanism that is not considered at present in projections of future climate change.
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Compassion fade and the challenge of environmental conservation
Ezra Markowitz et al.
Judgment and Decision Making, July 2013, Pages 397–406
Abstract:
Compassion shown towards victims often decreases as the number of individuals in need of aid increases, identifiability of the victims decreases, and the proportion of victims helped shrinks. Such “compassion fade” may hamper individual-level and collective responses to pressing large-scale crises. To date, research on compassion fade has focused on humanitarian challenges; thus, it remains unknown whether and to what extent compassion fade emerges when victims are non-human others. Here we show that compassion fade occurs in the environmental domain, but only among non-environmentalists. These findings suggest that compassion fade may challenge our collective ability and willingness to confront the major environmental problems we face, including climate change. The observed moderation effect of environmental identity further indicates that compassion fade may present a significant psychological barrier to building broad public support for addressing these problems. Our results highlight the importance of bringing findings from the field of judgment and decision making to bear on pressing societal issues.
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Future reef decalcification under a business-as-usual CO2 emission scenario
Sophie Dove et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Increasing atmospheric partial pressure of CO2 (pCO2) is a major threat to coral reefs, but some argue that the threat is mitigated by factors such as the variability in the response of coral calcification to acidification, differences in bleaching susceptibility, and the potential for rapid adaptation to anthropogenic warming. However the evidence for these mitigating factors tends to involve experimental studies on corals, as opposed to coral reefs, and rarely includes the influence of multiple variables (e.g., temperature and acidification) within regimes that include diurnal and seasonal variability. Here, we demonstrate that the inclusion of all these factors results in the decalcification of patch-reefs under business-as-usual scenarios and reduced, although positive, calcification under reduced-emission scenarios. Primary productivity was found to remain constant across all scenarios, despite significant bleaching and coral mortality under both future scenarios. Daylight calcification decreased and nocturnal decalcification increased sharply from the preindustrial and control conditions to the future scenarios of low (reduced emissions) and high (business-as-usual) increases in pCO2. These changes coincided with deeply negative carbonate budgets, a shift toward smaller carbonate sediments, and an increase in the abundance of sediment microbes under the business-as-usual emission scenario. Experimental coral reefs demonstrated highest net calcification rates and lowest rates of coral mortality under preindustrial conditions, suggesting that reef processes may not have been able to keep pace with the relatively minor environmental changes that have occurred during the last century. Taken together, our results have serious implications for the future of coral reefs under business-as-usual environmental changes projected for the coming decades and century.
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The other ocean acidification problem: CO2 as a resource among competitors for ecosystem dominance
Sean Connell et al.
Philosophical Transactions of the Royal Society: Biological Sciences, 5 October 2013
Abstract:
Predictions concerning the consequences of the oceanic uptake of increasing atmospheric carbon dioxide (CO2) have been primarily occupied with the effects of ocean acidification on calcifying organisms, particularly those critical to the formation of habitats (e.g. coral reefs) or their maintenance (e.g. grazing echinoderms). This focus overlooks direct and indirect effects of CO2 on non-calcareous taxa that play critical roles in ecosystem shifts (e.g. competitors). We present the model that future atmospheric [CO2] may act as a resource for mat-forming algae, a diverse and widespread group known to reduce the resilience of kelp forests and coral reefs. We test this hypothesis by combining laboratory and field CO2 experiments and data from ‘natural’ volcanic CO2 vents. We show that mats have enhanced productivity in experiments and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions. The benefits of CO2 are likely to vary among species of producers, potentially leading to shifts in species dominance in a high CO2 world. We explore how ocean acidification combines with other environmental changes across a number of scales, and raise awareness of CO2 as a resource whose change in availability could have wide-ranging community consequences beyond its direct effects.
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Long-term spatial and temporal trends in frost indices in Kansas, USA
Aavudai Anandhi et al.
Climatic Change, September 2013, Pages 169-181
Abstract:
Frost indices such as number of frost days (nFDs), number of frost-free days (nFFDs), last spring freeze (LSF), first fall freeze (FFF), and growing-season length (GSL) were calculated using daily minimum air temperature (Tmin) from 23 centennial weather stations across Kansas during four time periods (through 1919, 1920–1949, 1950–1979, and 1980–2009). A frost day is defined as a day with Tmin < 0 °C. The long- and short-term trends in frost indices were analyzed at monthly, seasonal, and annual timescales. Probability of occurrence of the indices was analyzed at 5 %, 25 %, 50 %, 75 %, and 95 %. Results indicated a general increase in Tmin from 1900 through 2009 causing a decrease in nFDs. LSF and FFF occurred earlier and later than normal in the year, respectively, thereby resulting in an increase in GSL. In general, northwest Kansas recorded the greatest nFD and lowest Tmin, whereas southeast Kansas had the lowest nFD and highest Tmin; however, the magnitude of the trends in these indices varied with location, time period, and time scales. Based on the long-term records in most stations, LSF occurred earlier by 0.1–1.9 days/decade, FFF occurred later by 0.2–0.9 day/decade, and GSL was longer by 0.1–2.5 day/decade. At the 50 % probability level, Independence in the south-eastern part of Kansas had the earliest LSF (6 April), latest FFF (29 October) and longest GSL (207 days). Oberlin (north-western Kansas) recorded the shortest GSL (156 days) and earliest FFF (7 October) had the latest LSF (2 May) at the 50 % probability level. A positive correlation was observed for combinations of indices (LSF and GSL) and elevation, whereas a negative correlation was found between FFF and elevation.
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Sea surface height evidence for long-term warming effects of tropical cyclones on the ocean
Wei Mei et al.
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Tropical cyclones have been hypothesized to influence climate by pumping heat into the ocean, but a direct measure of this warming effect is still lacking. We quantified cyclone-induced ocean warming by directly monitoring the thermal expansion of water in the wake of cyclones, using satellite-based sea surface height data that provide a unique way of tracking the changes in ocean heat content on seasonal and longer timescales. We find that the long-term effect of cyclones is to warm the ocean at a rate of 0.32 ± 0.15 PW between 1993 and 2009, i.e., ∼23 times more efficiently per unit area than the background equatorial warming, making cyclones potentially important modulators of the climate by affecting heat transport in the ocean–atmosphere system. Furthermore, our analysis reveals that the rate of warming increases with cyclone intensity. This, together with a predicted shift in the distribution of cyclones toward higher intensities as climate warms, suggests the ocean will get even warmer, possibly leading to a positive feedback.
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Will Future Climate Favor More Erratic Wildfires in the Western United States?
Lifeng Luo et al.
Journal of Applied Meteorology and Climatology, forthcoming
Abstract:
Wildfires that occurred over the western US during August 2012 were fewer in number but larger in size, as compared to all other Augusts in the 21st century. This unique characteristic, along with the tremendous property damage and potential loss of life due to large wildfires with erratic behavior, raised the question whether future climate will favor rapid wildfire growth so that similar wildfire activities may become more frequent as climate changes. This study addresses this question by examining differences in the climatological distribution of the Haines Index (HI) between the current and projected future climate over the western US. The HI, ranging from 2 to 6, was designed to characterize dry, unstable air in the lower atmosphere which may contribute to erratic or extreme fire behavior. A shift in HI distribution from low values (2, 3) to higher values (5, 6) would indicate an increased risk for rapid wildfire growth and spread. Haines Index distributions are calculated from simulations of current (1971-2000) and future (2041-2070) climate using multiple regional climate models (RCMs) in the North American Regional Climate Change Assessment Program (NARCCAP). Despite some differences among the projections, the simulations indicate that there may be not only more days but also more consecutive days with HI ≥ 5 during August in the future. This suggests that future atmospheric environments will be more conducive to erratic wildfires in the mountainous regions of the western US.
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Interhemispheric Temperature Asymmetry over the Twentieth Century and in Future Projections
Andrew Friedman et al.
Journal of Climate, August 2013, Pages 5419–5433
Abstract:
The temperature contrast between the Northern and Southern Hemispheres — the interhemispheric temperature asymmetry (ITA) — is an emerging indicator of global climate change, potentially relevant to the Hadley circulation and tropical rainfall. The authors examine the ITA in historical observations and in phases 3 and 5 of the Coupled Model Intercomparison Project (CMIP3 and CMIP5) simulations. The observed annual-mean ITA (north minus south) has varied within a 0.8°C range and features a significant positive trend since 1980. The CMIP multimodel ensembles simulate this trend, with a stronger and more realistic signal in CMIP5. Both ensembles project a continued increase in the ITA over the twenty-first century, well outside the twentieth-century range. The authors mainly attribute this increase to the uneven spatial impacts of greenhouse forcing, which result in amplified warming in the Arctic and northern landmasses. The CMIP5 specific-forcing simulations indicate that, before 1980, the greenhouse-forced ITA trend was primarily countered by anthropogenic aerosols. The authors also identify an abrupt decrease in the observed ITA in the late 1960s, which is generally not present in the CMIP simulations; it suggests that the observed drop was caused by internal variability. The difference in the strengths of the northern and southern Hadley cells covaries with the ITA in the CMIP5 simulations, in accordance with previous findings; the authors also find an association with the hemispheric asymmetry in tropical rainfall. These relationships imply a northward shift in tropical rainfall with increasing ITA in the twenty-first century, though this result is difficult to separate from the response to global-mean temperature change.
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Contribution of solar radiation to decadal temperature variability over land
Kaicun Wang & Robert Dickinson
Proceedings of the National Academy of Sciences, forthcoming
Abstract:
Global air temperature has become the primary metric for judging global climate change. The variability of global temperature on a decadal timescale is still poorly understood. This paper examines further one suggested hypothesis, that variations in solar radiation reaching the surface (Rs) have caused much of the observed decadal temperature variability. Because Rs only heats air during the day, its variability is plausibly related to the variability of diurnal temperature range (daily maximum temperature minus its minimum). We show that the variability of diurnal temperature range is consistent with the variability of Rs at timescales from monthly to decadal. This paper uses long comprehensive datasets for diurnal temperature range to establish what has been the contribution of Rs to decadal temperature variability. It shows that Rs over land globally peaked in the 1930s, substantially decreased from the 1940s to the 1970s, and changed little after that. Reduction of Rs caused a reduction of more than 0.2 °C in mean temperature during May to October from the 1940s through the 1970s, and a reduction of nearly 0.2 °C in mean air temperature during November to April from the 1960s through the 1970s. This cooling accounts in part for the near-constant temperature from the 1930s into the 1970s. Since then, neither the rapid increase in temperature from the 1970s through the 1990s nor the slowdown of warming in the early twenty-first century appear to be significantly related to changes of Rs.
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Revisiting the weather effect on energy consumption: Implications for the impact of climate change
Robert Kaufmann et al.
Energy Policy, forthcoming
Abstract:
We revisit statistical estimates for the relation between weather and energy consumption in Massachusetts using times series for heating degree hours that are calculated from hourly data with different set points and set backs. Using hourly values to calculate heating degree hours supports models that generate more accurate out-of-sample forecasts than models estimated from time series for heating degree-days calculated the traditional way. Furthermore, the set point and set back used to calculate heating degree hours generates statistically measurable differences in the accuracy of out-of-sample forecasts. These results indicate that assuming a set point of 65 °F biases statistical estimates for the effect of a warming climate on energy use. We also quantify a new mechanism by which climate change will affect energy use — the temperature of tap water. As climate warms, the temperature of tap water that supplies hot water tanks rises, which reduces the amount of energy consumed to provide hot water. Finally, we use the statistical models to generate a spatial (1 km×1 km) and temporal (hourly) downscaling of carbon emissions that will be used to simulate a model for atmospheric transport and validate our understanding of the sources and sinks of carbon for the urban atmosphere.
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Observed changes in the albedo of the Arctic sea-ice zone for the period 1982–2009
Aku Riihelä, Terhikki Manninen & Vesa Laine
Nature Climate Change, forthcoming
Abstract:
The surface albedo of the Arctic sea-ice zone is a crucial component in the energy budget of the Arctic region. The treatment of sea-ice albedo has been identified as an important source of variability in the future sea-ice mass loss forecasts in coupled climate models. There is a clear need to establish data sets of Arctic sea-ice albedo to study the changes based on observational data and to aid future modelling efforts. Here we present an analysis of observed changes in the mean albedo of the Arctic sea-ice zone using a data set consisting of 28 years of homogenized satellite data. Along with the albedo reduction resulting from the well-known loss of late-summer sea-ice cover, we show that the mean albedo of the remaining Arctic sea-ice zone is decreasing. The change per decade in the mean August sea-ice zone albedo is −0.029±0.011. All albedo trends, except for the sea-ice zone in May, are significant with a 99% confidence interval. Variations in mean sea-ice albedo can be explained using sea-ice concentration, surface air temperature and elapsed time from onset of melt as drivers.