23 research outputs found

    Quantifying the temperature-independent effect of stratospheric aerosol geoengineering on global-mean precipitation in a multi-model ensemble

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    This is the final version of the article. Available from the publisher via the DOI in this record.The reduction in global-mean precipitation when stratospheric aerosol geoengineering is used to counterbalance global warming from increasing carbon dioxide concentrations has been mainly attributed to the temperature-independent effect of carbon dioxide on atmospheric radiative cooling. We demonstrate here that stratospheric sulphate aerosol itself also acts to reduce global-mean precipitation independent of its effects on temperature. The temperature-independent effect of stratospheric aerosol geoenginering on global-mean precipitation is calculated by removing temperature-dependent effects from climate model simulations of the Geoengineering Model Intercomparison Project (GeoMIP). When sulphate aerosol is injected into the stratosphere at a rate of 5 Tg SO2 per year the aerosol reduces global-mean precipitation by approximately 0.2 %, though multiple ensemble members are required to separate this effect from internal variability. For comparison, the precipitation reduction from the temperature-independent effect of increasing carbon dioxide concentrations under the RCP4.5 scenario of the future is approximately 0.5%. Thetemperature-independent effect of stratospheric sulphate aerosol arises from the aerosol's effect on tropospheric radiative cooling. Radiative transfer calculations show this is mainly due to increasing downward emission of infrared radiation by the aerosol, but there is also a contribution from the stratospheric warming the aerosol causes. Our results suggest climate model simulations of solar dimming can capture the main features of the global-mean precipitation response to stratospheric aerosol geoengineering.Natural Environment Research Council (NERC)Engineering and Physical Sciences Research Council (EPSRC)We thank Hugo Lambert and Mat Collins for useful discussions, and Ulrike Niemeier for extensive help with data access. A Ferraro was supported by the Natural Environment Research Council PROBEC grant (NE/K016016/1). H Griffiths was supported by the Engineering and Physical Sciences Research Council Vacation Bursary Scheme. We thank all the climate modelling groups for conducting the GeoMIP simulations and making their output available. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modelling groups (listed in table 1 of this paper) for producing and making available their model output. For CMIP the US Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led development of software infrastructure in partnership with the Global Organization for Earth System Science Portal

    Quantifying the temperature-independent effect of stratospheric aerosol geoengineering on global-mean precipitation in a multi-model ensemble

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    This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record. The final version is available on open access.The reduction in global-mean precipitation when stratospheric aerosol geoengineering is used to counterbalance global warming from increasing carbon dioxide concentrations has been mainly attributed to the temperature-independent effect of carbon dioxide on atmospheric radiative cooling. We demonstrate here that stratospheric sulphate aerosol itself also acts to reduce global-mean precipitation independent of its effects on temperature. The temperature-independent effect of stratospheric aerosol geoenginering on global-mean precipitation is calculated by removing temperature-dependent effects from climate model simulations of the Geoengineering Model Intercomparison Project (GeoMIP). When sulphate aerosol is injected into the stratosphere at a rate of 5 Tg SO2 per year the aerosol reduces global-mean precipitation by approximately 0.2 %, though multiple ensemble members are required to separate this effect from internal variability. For comparison, the precipitation reduction from the temperature-independent effect of increasing carbon dioxide concentrations under the RCP4.5 scenario of the future is approximately 0.5%. Thetemperature-independent effect of stratospheric sulphate aerosol arises from the aerosol's effect on tropospheric radiative cooling. Radiative transfer calculations show this is mainly due to increasing downward emission of infrared radiation by the aerosol, but there is also a contribution from the stratospheric warming the aerosol causes. Our results suggest climate model simulations of solar dimming can capture the main features of the global-mean precipitation response to stratospheric aerosol geoengineering.Natural Environment Research Council (NERC)Engineering and Physical Sciences Research Council (EPSRC

    Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors, and sulfate and titania aerosols

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    Copyright © 2015 The AuthorsThe impact on the dynamics of the stratosphere of three approaches to geoengineering by solar radiation management is investigated using idealized simulations of a global climate model. The approaches are geoengineering with sulfate aerosols, titania aerosols, and reduction in total solar irradiance (representing mirrors placed in space). If it were possible to use stratospheric aerosols to counterbalance the surface warming produced by a quadrupling of atmospheric carbon dioxide concentrations, tropical lower stratospheric radiative heating would drive a thermal wind response which would intensify the stratospheric polar vortices. In the Northern Hemisphere this intensification results in strong dynamical cooling of the polar stratosphere. Northern Hemisphere stratospheric sudden warming events become rare (one and two in 65 years for sulfate and titania, respectively). The intensification of the polar vortices results in a poleward shift of the tropospheric midlatitude jets in winter. The aerosol radiative heating enhances the tropical upwelling in the lower stratosphere, influencing the strength of the Brewer-Dobson circulation. In contrast, solar dimming does not produce heating of the tropical lower stratosphere, and so there is little intensification of the polar vortex and no enhanced tropical upwelling. The dynamical response to titania aerosol is qualitatively similar to the response to sulfate.Natural Environment Research Counci

    Physical Mechanisms of Tropical Climate Feedbacks Investigated Using Temperature and Moisture Trends

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    ArticleOpen access articleTropical climate feedback mechanisms are assessed using satellite-observed and model-simulated trends in tropical tropospheric temperature from the MSU/AMSU instruments and upper-tropospheric humidity from the HIRS instruments. Despite discrepancies in the rates of tropospheric warming between observations and models, both are consistent with constant relative humidity over the period 1979--2008. Because uncertainties in satellite-observed tropical-mean trends preclude a constraint on tropical-mean trends in models we also explore regional features of the feedbacks. The regional pattern of the lapse rate feedback is primarily determined by the regional pattern of surface temperature changes, as tropical atmospheric warming is relatively horizontally uniform. The regional pattern of the water vapor feedback is influenced by the regional pattern of precipitation changes, with variations of 1--2 W m-2 K-1 across the Tropics (compared to a tropical-mean feedback magnitude of 3.3--4 W m-2 K-1). Thus the geographical patterns of water vapor and lapse rate feedbacks are not correlated, but when the feedbacks are calculated in precipitation percentiles rather than in geographical space they are anti-correlated, with strong positive water vapor feedback associated with strong negative lapse rate feedback. The regional structure of the feedbacks is not related to the strength of the tropical-mean feedback in a subset of the climate models from the CMIP5 archive. Nevertheless the approach constitutes a useful process-based test of climate models and has the potential to be extended to constrain regional climate projections.Natural Environment Research Council (NERC

    Strong detection of the CMB lensingxgalaxy weak lensingcross-correlation from ACT-DR4,PlanckLegacy and KiDS-1000

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    We measure the cross-correlation between galaxy weak lensing data from the Kilo Degree Survey (KiDS-1000, DR4) and cosmic microwave background (CMB) lensing data from the Atacama Cosmology Telescope (ACT, DR4) and the Planck Legacy survey. We use two samples of source galaxies, selected with photometric redshifts, (0.1<zB<1.2)(0.1<z_{\rm B}<1.2) and (1.2<zB<2)(1.2<z_{\rm B}<2), which produce a combined detection significance of the CMB lensing/weak galaxy lensing cross-spectrum of 7.7σ7.7\sigma. With the lower redshift galaxy sample, for which the cross-correlation is detected at a significance of 5.3σ5.3\sigma, we present joint cosmological constraints on the matter density parameter, Ωm\Omega_{\rm m}, and the matter fluctuation amplitude parameter, σ8\sigma_8, marginalising over three nuisance parameters that model our uncertainty in the redshift and shear calibration, and the intrinsic alignment of galaxies. We find our measurement to be consistent with the best-fitting flat Λ\LambdaCDM cosmological models from both Planck and KiDS-1000. We demonstrate the capacity of CMB-weak lensing cross-correlations to set constraints on either the redshift or shear calibration, by analysing a previously unused high-redshift KiDS galaxy sample (1.2<zB<2)(1.2<z_{\rm B}<2), with the cross-correlation detected at a significance of 7σ7\sigma. This analysis provides an independent assessment for the accuracy of redshift measurements in a regime that is challenging to calibrate directly owing to known incompleteness in spectroscopic surveys.Comment: 13 pages, 9 figures, 1 tables, submitted to A&

    The E-ELT first light spectrograph HARMONI: capabilities and modes

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    Trabajo presentado en SPIE Astronomical Telescopes, celebrado en San Diego (California), del 26 de junio al 1 de julio de 2016HARMONI is the E-ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R 3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 - 2.4 ¿m wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument's technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline

    Fraction of global area, population and GDP affected by different outcomes of geoengineering.

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    <p>Each climate model simulation has a pair of bars. The left-hand bar shows the ‘benign’ and ‘effective’ outcomes, i.e. where geoengineering reduces risk. The right-hand bar shows the ‘damaging’ and ‘ineffective’ outcomes, i.e. where geoengineering increases risk. Regions where neither the response to 4CO<sub>2</sub> or geoengineering are statistically significant at the 95% level are neglected, so the bars do not sum to 1.0.</p
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