Climatic impacts of stratospheric geoengineering with sulfate, black carbon and titania injection

In this paper, we examine the potential climatic effects of geoengineering by sulfate, black carbon and titania injection against a baseline RCP8.5 scenario. We use the HadGEM2-CCS model to simulate scenarios in which the top-of-the-atmosphere radiative imbalance due to rising greenhouse gas concentrations is offset by sufficient aerosol injection throughout the 2020–2100 period. We find that the global-mean temperature is effectively maintained at historical levels for the entirety of the period for all 3 aerosol-injection scenarios, though there are a wide range of side-effects which are discussed in detail. The most prominent conclusion is that although the BC injection rate necessary to produce an equivalent global mean temperature-response is much lower, the severity of stratospheric temperature changes (> +70 °C) and precipitation impacts effectively exclude BC from being a viable option for geoengineering. Additionally, while it has been suggested that titania would be an effective particle because of its high scattering efficiency, it also efficiently absorbs solar ultraviolet radiation producing a significant stratospheric warming (> +20 °C). As injection rates for titania are close to those for sulfate, there appears little benefit of using titania when compared to injection of sulfur dioxide, which has the added benefit of being well modelled through extensive research that has been carried out on naturally occurring explosive volcanic eruptions.The authors would like to thank Valentina Aquila for supplying AVHRR and SAGE data, and to Peter Cox, Angus Ferraro, David Keith and Alan Robock for helpful discussions. A. C. Jones was supported by a Met Office/NERC CASE (ref. 580 009 183) PhD studentship; J. M. Haywood and A. Jones were supported by the Joint UK DECC/Defra Met Office Hadley Centre Climate Programme (GA01101)

Climate impacts of geoengineering marine stratocumulus clouds

Copyright © 2000 American Geophysical Union[1] Theoretical potential geoengineering solutions to the global warming problem have recently been proposed. Here, we present an idealized study of the climate response to deliberately seeding large-scale stratocumulus cloud decks in the North Pacific, South Pacific, and South Atlantic, thereby inducing cooling via aerosol indirect effects. Atmosphere-only, atmosphere/mixed-layer ocean, and fully coupled atmosphere/ocean versions of the Met Office Hadley Centre model are used to investigate the radiative forcing, climate efficacy, and regional response of temperature, precipitation, and net primary productivity to such geoengineering. The radiative forcing simulations indicate that, for our parameterization of aerosol indirect effects, up to 35% of the radiative forcing due to current levels of greenhouse gases could be offset by stratocumulus modification. Equilibrium simulations with the atmosphere/mixed-layer ocean model, wherein each of the three stratocumulus sheets is modified in turn, reveal that the most efficient cooling per unit radiative forcing occurs when the South Pacific stratocumulus sheet is modified. Transient coupled model simulations suggest that geoengineering all three stratocumulus areas delays the simulated global warming by about 25 years. These simulations also indicate that, while some areas experience increases in precipitation and net primary productivity, sharp decreases are simulated in South America, with particularly detrimental impacts on the Amazon rain forest. These results show that, while some areas benefit from geoengineering, there are significant areas where the response could be very detrimental with implications for the practical applicability of such a scheme

A latest Cretaceous to earliest Paleogene dinoflagellate cyst zonation of Antarctica, and implications for phytoprovincialism in the high southern latitudes

The thickest uppermost Cretaceous to lowermost Paleogene (Maastrichtian to Danian) sedimentary succession in the world is exposed on southern Seymour Island (65° South) in the James Ross Basin, Antarctic Peninsula. This fossiliferous shallow marine sequence, which spans the Cretaceous–Paleogene boundary, has allowed a high-resolution analysis of well-preserved marine palynomorphs. Previous correlation of Cretaceous–Paleogene marine palynomorph assemblages in the south polar region relied on dinoflagellate cyst biozonations from New Zealand and southern Australia. The age model of the southern Seymour Island succession is refined and placed within the stratigraphical context of the mid to high southern palaeolatitudes. Quantitative palynological analysis of a new 1102 m continuous stratigraphical section comprising the uppermost Snow Hill Island Formation and the López de Bertodano Formation (Marambio Group) across southern Seymour Island was undertaken. We propose the first formal late Maastrichtian to early Danian dinoflagellate cyst zonation scheme for the Antarctic based on this exceptional succession. Two new late Maastrichtian zones, including three subzones, and one new early Danian zone are defined. The oldest beds correlate well with the late Maastrichtian of New Zealand. In a wider context, a new South Polar Province based on Maastrichtian to Danian dinoflagellate cysts is proposed, which excludes most southern South American marine palynofloras. This interpretation is supported by models of ocean currents around Antarctica and implies an unrestricted oceanic connection across Antarctica between southern South America and the Tasman Sea

Smoke and clouds above the Southeast Atlantic: upcoming field campaigns probe absorbing aerosol’s impact on climate

ArticleFrom July through October, smoke from biomass burning fires on the southern African sub-continent are transported westward through the free troposphere over one of the largest stratocumulus cloud decks on our planet. Biomass burning aerosol (smoke) absorbs shortwave radiation efficiently. This fundamental property implicates smoke within myriad small-scale processes with potential large-scale impacts on climate that are not yet well-understood. A coordinated, international team of scientists from the United States, United Kingdom, France, South Africa and Namibia will provide an unprecedented interrogation of this smoke-and-cloud regime from 2016 to 2018, using multiple aircraft and surface-based instrumentation suites to span much of the breadth of the southeast Atlantic

Climate response to off-equatorial stratospheric sulfur injections in three Earth system models – Part 2: Stratospheric and free-tropospheric response

The paper constitutes Part 2 of a study performing a first systematic inter-model comparison of the atmospheric responses to stratospheric aerosol injection (SAI) at various single latitudes in the tropics, as simulated by three state-of-the-art Earth system models – CESM2-WACCM6, UKESM1.0, and GISS-E2.1-G. Building on Part 1 (Visioni et al., 2023) we demonstrate the role of biases in the climatological circulation and specific aspects of the model microphysics in driving the inter-model differences in the simulated sulfate distributions. We then characterize the simulated changes in stratospheric and free-tropospheric temperatures, ozone, water vapor, and large-scale circulation, elucidating the role of the above aspects in the surface SAI responses discussed in Part 1. We show that the differences in the aerosol spatial distribution can be explained by the significantly faster shallow branches of the Brewer–Dobson circulation in CESM2, a relatively isolated tropical pipe and older tropical age of air in UKESM, and smaller aerosol sizes and relatively stronger horizontal mixing (thus very young stratospheric age of air) in the two GISS versions used. We also find a large spread in the magnitudes of the tropical lower-stratospheric warming amongst the models, driven by microphysical, chemical, and dynamical differences. These lead to large differences in stratospheric water vapor responses, with significant increases in stratospheric water vapor under SAI in CESM2 and GISS that were largely not reproduced in UKESM. For ozone, good agreement was found in the tropical stratosphere amongst the models with more complex microphysics, with lower stratospheric ozone changes consistent with the SAI-induced modulation of the large-scale circulation and the resulting changes in transport. In contrast, we find a large inter-model spread in the Antarctic ozone responses that can largely be explained by the differences in the simulated latitudinal distributions of aerosols as well as the degree of implementation of heterogeneous halogen chemistry on sulfate in the models. The use of GISS runs with bulk microphysics demonstrates the importance of more detailed treatment of aerosol processes, with contrastingly different stratospheric SAI responses to the models using the two-moment aerosol treatment; however, some problems in halogen chemistry in GISS are also identified that require further attention. Overall, our results contribute to an increased understanding of the underlying physical mechanisms as well as identifying and narrowing the uncertainty in model projections of climate impacts from SAI.</p

An exploratory survey on the awareness and usage of clinical practice guidelines among clinical pharmacists

Background: The NHLBI has not developed clinical practice guidelines since 2007. As a result, multiple organizations have released competing guidelines. This has created confusion and debate among clinicians as to which recommendations are most applicable for practice. Objectives: To explore preliminary attitudes, awareness, and usage of clinical practice guidelines in practice and teaching for hypertension, dyslipidemia and asthma among clinical pharmacists. Methods: Clinical pharmacists across the US were surveyed electronically over a two week period in Spring 2019 regarding utilization and knowledge of practice guidelines for hypertension, dyslipidemia, and asthma. Clinical cases were included to evaluate application of guidelines. Descriptive statistics, Chi-square analysis, and Wilcoxon signed-rank test were conducted. Statistical significance level was set to 0.01 to account for multiple tests conducted on the same survey participants. Results: Forty-eight, 34, and 28 pharmacists voluntarily completed hypertension, dyslipidemia, and asthma survey questions, respectively. Interactions by disease state (p \u3c 0.001) revealed more pharmacists (93%) reporting to have ≤50% patient load in managing asthma and more pharmacists (95%) had read the full summary/report of the most recent hypertension guideline. Primary reasons why the most recent guideline was not selected were also significantly different by disease state (interaction; p \u3c 0.001). For dyslipidemia and asthma, pharmacists had a higher mean rating of agreement (p \u3c0.007) in having the most confidence in the most recent as compared to older guidelines. Proportionally more clinical cases were answered correctly (interaction; p \u3c0.001) when pharmacists applied the most recent guideline for hypertension (84%), while the opposite outcome was found for asthma (27%). Conclusion: While more pharmacists selected the most recent guideline for practice and teaching, there was inconsistent application of guidelines to clinical cases. Further studies with a larger representation of pharmacists are warranted to more definitively determine factors influencing guideline preference and usage

Impacts of hemispheric solar geoengineering on tropical cyclone frequency

Solar geoengineering refers to a range of proposed methods for counteracting global warming by artificially reducing sunlight at Earth’s surface. The most widely known SG proposal is stratospheric aerosol injection (SAI) which has impacts analogous to those from volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic tropical cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model and various TC identification methods. We show that a robust result from all of the methods is that SAI applied to the southern hemisphere would enhance TC frequency relative to a global SAI application, and vice versa for SAI in the northern hemisphere. Our results reemphasize the perils of regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments

The impact of equilibrating hemispheric albedos on tropical performance in the HadGEM2-ES coupled climate model

AcceptedArticle in Press©2015. The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.©2015. The Authors. The Earth's hemispheric reflectances are equivalent to within±0.2Wm-2, even though the Northern Hemisphere contains a greater proportion of higher reflectance land areas, because of greater cloud cover in the Southern Hemisphere. This equivalence is unlikely to be by chance, but the reasons are open to debate. Here we show that equilibrating hemispheric albedos in the Hadley Centre Global Environment Model version 2-Earth System coupled climate model significantly improves what have been considered longstanding and apparently intractable model biases. Monsoon precipitation biases over all continental land areas, the penetration of monsoon rainfall across the Sahel, the West African monsoon "jump", and indicators of hurricane frequency are all significantly improved. Mechanistically, equilibrating hemispheric albedos improves the atmospheric cross-equatorial energy transport and increases the supply of tropical atmospheric moisture to the Hadley cell. We conclude that an accurate representation of the cross-equatorial energy transport appears to be critical if tropical performance is to be improved