Methods to estimate acclimatization to urban heat island effects on heat- and cold-related mortality

Background: Investigators have examined whether heat mortality risk is increased in neighborhoods subject to the urban heat island (UHI) effect but have not identified degrees of difference in susceptibility to heat and cold between cool and hot areas, which we call acclimatization to the UHI. Objectives: We developed methods to examine and quantify the degree of acclimatization to heat- and cold-related mortality in relation to UHI anomalies and applied these methods to London, UK. Methods: Case–crossover analyses were undertaken on 1993–2006 mortality data from London UHI decile groups defined by anomalies from the London average of modeled air temperature at a 1-km grid resolution. We estimated how UHI anomalies modified excess mortality on cold and hot days for London overall and displaced a fixed-shape temperature-mortality function (“shifted spline” model). We also compared the observed associations with those expected under no or full acclimatization to the UHI. Results: The relative risk of death on hot versus normal days differed very little across UHI decile groups. A 1°C UHI anomaly multiplied the risk of heat death by 1.004 (95% CI: 0.950, 1.061) (interaction rate ratio) compared with the expected value of 1.070 (1.057, 1.082) if there were no acclimatization. The corresponding UHI interaction for cold was 1.020 (0.979, 1.063) versus 1.030 (1.026, 1.034) (actual versus expected under no acclimatization, respectively). Fitted splines for heat shifted little across UHI decile groups, again suggesting acclimatization. For cold, the splines shifted somewhat in the direction of no acclimatization, but did not exclude acclimatization. Conclusions: We have proposed two analytical methods for estimating the degree of acclimatization to the heat- and cold-related mortality burdens associated with UHIs. The results for London suggest relatively complete acclimatization to the UHI effect on summer heat–related mortality, but less clear evidence for cold–related mortality

A Deep Learning Parameterization for Ozone Dry Deposition Velocities

The loss of ozone to terrestrial and aquatic systems, known as dry deposition, is a highly uncertain process governed by turbulent transport, interfacial chemistry, and plant physiology. We demonstrate the value of using Deep Neural Networks (DNN) in predicting ozone dry deposition velocities. We find that a feedforward DNN trained on observations from a coniferous forest site (Hyytiala, Finland) can predict hourly ozone dry deposition velocities at a mixed forest site (Harvard Forest, Massachusetts) more accurately than modern theoretical models, with a reduction in the normalized mean bias (0.05 versus similar to 0.1). The same DNN model, when driven by assimilated meteorology at 2 degrees x 2.5 degrees spatial resolution, outperforms the Wesely scheme as implemented in the GEOS-Chem model. With more available training data from other climate and ecological zones, this methodology could yield a generalizable DNN suitable for global models. Plain Language Summary Ozone in the lower atmosphere is a toxic pollutant and greenhouse gas. In this work, we use a machine learning technique known as deep learning, to simulate the loss of ozone to Earth's surface. We show that our deep learning simulation of this loss process outperforms existing traditional models and demonstrate the opportunity for using machine learning to improve our understanding of the chemical composition of the atmosphere.Peer reviewe

Differences in behavior and distribution of permafrost-related lakes in Central Yakutia and their response to climatic drivers

The Central Yakutian permafrost landscape is rapidly being modified by land use and global warming, but small-scale thermokarst process variability and hydrological conditions are poorly understood. We analyze lake-area changes and thaw subsidence of young thermokarst lakes on ice-complex deposits (yedoma lakes) in comparison to residual lakes in alas basins during the last 70 years for a local study site and we record regional lake size and distribution on different ice-rich permafrost terraces using satellite and historical airborne imagery. Statistical analysis of climatic and ground-temperature data identified driving factors of yedoma- and alas-lake changes. Overall, lake area is larger today than in 1944 but alas-lake levels have oscillated greatly over 70 years, with a mean alas-lake-radius change rate of 1.663.0 m/yr. Anthropogenic disturbance and forest degradation initiated, and climate forced rapid, continuous yedoma-lake growth. The mean yedoma lake-radius change rate equals 1.261.0 m/yr over the whole observation period. Mean thaw subsidence below yedoma lakes is 6.261.4 cm/yr. Multiple regression analysis suggests that winter precipitation, winter temperature, and active-layer properties are primary controllers of area changes in both lake types; summer weather and permafrost conditions additionally influence yedoma-lake growth rates. The main controlling factors of alas-lake changes are unclear due to larger catchment areas and subsurface hydrological conditions. Increasing thermokarst activity is currently linked to older terraces with higher ground-ice contents, but thermokarst activity will likely stay high and wet conditions will persist within the near future in Central Yakutian alas basins

Gas valves, forests and global change: a commentary on Jarvis (1976) 'The interpretation of the variations in leaf water potential and stomatal conductance found in canopies in the field'.

Microscopic turgor-operated gas valves on leaf surfaces-stomata-facilitate gas exchange between the plant and the atmosphere, and respond to multiple environmental and endogenous cues. Collectively, stomatal activities affect everything from the productivity of forests, grasslands and crops to biophysical feedbacks between land surface vegetation and climate. In 1976, plant physiologist Paul Jarvis reported an empirical model describing stomatal responses to key environmental and plant conditions that predicted the flux of water vapour from leaves into the surrounding atmosphere. Subsequent theoretical advances, building on this earlier approach, established the current paradigm for capturing the physiological behaviour of stomata that became incorporated into sophisticated models of land carbon cycling. However, these models struggle to accurately predict observed trends in the physiological responses of Northern Hemisphere forests to recent atmospheric CO2 increases, highlighting the need for improved representation of the role of stomata in regulating forest-climate interactions. Bridging this gap between observations and theory as atmospheric CO2 rises and climate change accelerates creates challenging opportunities for the next generation of physiologists to advance planetary ecology and climate science. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society

Constraints on the lake volume required for hydro-fracture through ice sheets

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L10501, doi:10.1029/2008GL036765.Water-filled cracks are an effective mechanism to drive hydro-fractures through thick ice sheets. Crack geometry is therefore critical in assessing whether a supraglacial lake contains a sufficient volume of water to keep a crack water-filled until it reaches the bed. In this study, we investigate fracture propagation using a linear elastic fracture mechanics model to calculate the dimensions of water-filled cracks beneath supraglacial lakes. We find that the cross-sectional area of water-filled cracks increases non-linearly with ice sheet thickness. Using these results, we place volumetric constraints on the amount of water necessary to drive cracks through ∼1 km of sub-freezing ice. For ice sheet regions under little tension, lakes larger than 0.25–0.80 km in diameter contain sufficient water to rapidly drive hydro-fractures through 1–1.5 km of subfreezing ice. This represents ∼98% of the meltwater volume held in supraglacial lakes in the central western margin of the Greenland Ice Sheet.Support for this research was provided by NSF and NASA (through ARC-0520077, ARC- 0531345, and ARC-520382) and by the Joint Initiative Awards Fund from the Andrew Mellon Foundation, and the WHOI Ocean and Climate Change Institute and Clark Arctic Research Initiative

Global warming and malaria: knowing the horse before hitching the cart

Speculations on the potential impact of climate change on human health frequently focus on malaria. Predictions are common that in the coming decades, tens – even hundreds – of millions more cases will occur in regions where the disease is already present, and that transmission will extend to higher latitudes and altitudes. Such predictions, sometimes supported by simple models, are persuasive because they are intuitive, but they sidestep factors that are key to the transmission and epidemiology of the disease: the ecology and behaviour of both humans and vectors, and the immunity of the human population. A holistic view of the natural history of the disease, in the context of these factors and in the precise setting where it is transmitted, is the only valid starting point for assessing the likely significance of future changes in climate

On the political feasibility of climate change mitigation pathways: Is it too late to keep warming below 1.5°C?

Keeping global warming below 1.5°C is technically possible but is it politically feasible? Understanding political feasibility requires answering three questions: (a) “Feasibility of what?,” (b) “Feasibility when and where?,” and (c) “Feasibility for whom?.” In relation to the 1.5°C target, these questions translate into (a) identifying specific actions comprising the 1.5°C pathways; (b) assessing the economic and political costs of these actions in different socioeconomic and political contexts; and (c) assessing the economic and institutional capacity of relevant social actors to bear these costs. This view of political feasibility stresses costs and capacities in contrast to the prevailing focus on benefits and motivations which mistakes desirability for feasibility. The evidence on the political feasibility of required climate actions is not systematic, but clearly indicates that the costs of required actions are too high in relation to capacities to bear these costs in relevant contexts. In the future, costs may decline and capacities may increase which would reduce political constraints for at least some solutions. However, this is unlikely to happen in time to avoid a temperature overshoot. Further research should focus on exploring the “dynamic political feasibility space” constrained by costs and capacities in order to find more feasible pathways to climate stabilization. This article is categorized under: The Carbon Economy and Climate Mitigation > Decarbonizing Energy and/or Reducing Demand

A quantitative assessment of uncertainties affecting estimates of global mean OH derived from methyl chloroform observations

We estimated the global abundance of OH by interpreting observations of methyl chloroform (MCF) from two networks using an inverse technique and a 3-D chemical transport model driven by assimilated meteorology. Our inversion approach optimized both the emissions of MCF and the abundance of OH. Because of an a priori overestimate of the latitudinal gradient by the model in the standard setup, the inversion lowers global emissions and the global sink due to OH. Optimized emissions are about 10 % lower than published inventories on average between 1988 and 1994, and the decrease in the sink suggested by the inversion implies an average lifetime for MCF (with respect to tropospheric OH) of about 6.9 years, 11-21 % longer than the 5.7-6.2 years reported in previous studies. Our results are driven by the need to match the observed latitudinal gradient of MCF while balancing the MCF budget. We find that these results depend on the a priori constraint placed on MCF emissions, the rate of interhemispheric mixing in the model, the interhemispheric distribution of OH assumed, and the model simulation of pollution events. Since these factors are highly uncertain, we believe that the level of understanding on global lifetimes of pollutants removed by OH is lower than might be implied by the narrow range of estimates for MCF lifetime in the literature. 2

Local and remote controls on observed Arctic warming

Copyright © 2012 American Geophysical UnionThe Arctic is warming two to four times faster than the global average. Debate continues on the relative roles of local factors, such as sea ice reductions, versus remote factors in driving, or amplifying, Arctic warming. This study examines the vertical profile and seasonality of observed tropospheric warming, and addresses its causes using atmospheric general circulation model simulations. The simulations enable the isolation and quantification of the role of three controlling factors of Arctic warming: 1) observed Arctic sea ice concentration (SIC) and sea surface temperature (SST) changes; 2) observed remote SST changes; and 3) direct radiative forcing (DRF) due to observed changes in greenhouse gases, ozone, aerosols, and solar output. Local SIC and SST changes explain a large portion of the observed Arctic near-surface warming, whereas remote SST changes explain the majority of observed warming aloft. DRF has primarily contributed to Arctic tropospheric warming in summer