Energy transport, polar amplification, and ITCZ shifts in the GeoMIP G1 ensemble

Russotto, Rick D.; Ackerman, Thomas P.

doi:10.5194/acp-18-2287-2018

Cited by 22 publications

(25 citation statements)

References 61 publications

(75 reference statements)

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“…Numerous modeling studies have been carried out both in the past and present to simulate the impacts of solar geoengineering on various climatic phenomena (Govindasamy et al 2003, Bala et al 2008, Lunt et al 2008, Curry et al 2014. In a few recent studies, solar geoengineering impacts on various aspects of the climate system have been explored, including the occurrence of extreme events (Curry et al 2014, circulation patterns and energy transport (Davis et al 2016, Smyth et al 2017, Guo et al 2018, Russotto and Ackerman 2018a, clouds and thermodynamics (Russotto and Ackerman 2018b), etc. While the above-mentioned studies have investigated some aspects of global precipitation change under global warming and solar geoengineering, likely changes in global precipitation seasonality has not yet been investigated.…”

Section: Introductionmentioning

confidence: 99%

Effects of global warming and solar geoengineering on precipitation seasonality

Bal

Pathak

Mishra

et al. 2019

Environ. Res. Lett.

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The effects of global warming and geoengineering on annual precipitation and its seasonality over different parts of the world are examined using the piControl, 4xCO 2 and G1 simulations from eight global climate models participating in the Geoengineering Model Intercomparison Project. Specifically, we have used relative entropy, seasonality index, duration of the peak rainy season and timing of the peak rainy season to investigate changes in precipitation characteristics under 4xCO 2 and G1 scenarios with reference to the piControl. In a 4xCO 2 world, precipitation is projected to increase over many parts of the globe, along with an increase in both the relative entropy and seasonality index. Further, in a 4xCO 2 world the increase in peak precipitation duration is found to be highest over the subpolar climatic region. However, over the tropical rain belt, the duration of the peak precipitation period is projected to decrease. Furthermore, there is a significant shift in the timing of the peak precipitation period by 15 days-2 months (forward) over many parts of the Northern Hemisphere except for over a few regions, such as North America and parts of Mediterranean countries, where a shift in the precipitation peak by 1-3 months (backward) is observed. However, solar geoengineering is found to significantly compensate many of the changes projected in a 4xCO 2 scenario. Solar geoengineering nullifies the precipitation increase to a large extent. Relative entropy and the seasonality index are almost restored back to that in the control simulations, although with small positive and negative deviations over different parts of the globe, thus, significantly nullifying the impact of 4xCO 2 . However, over some regions, such as northern parts of South America, the Arabian Sea and Southern Africa, geoengineering does not significantly nullify changes in the seasonality index seen in 4xCO 2 . Finally, solar geoengineering significantly compensates the changes in timing of the peak and duration of the peak precipitation seen in 4xCO 2 .

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Section: Introductionmentioning

confidence: 99%

Effects of global warming and solar geoengineering on precipitation seasonality

Bal

Pathak

Mishra

et al. 2019

Environ. Res. Lett.

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“…Weakening of the extratropical storm tracks would be expected to, for example, reduce wind extremes in midlatitudes but also possibly lead to less efficient ventilation of air pollution from the boundary layer (Leibensperger et al, 2008). A weakening of the storm tracks may also contribute to the decrease in low cloud fraction over the storm‐track regions (Russotto & Ackerman, 2018b) and weakened poleward energy transport (Russotto & Ackerman, 2018a) identified previously in the G1 experiment.…”

Section: Conclusion and Discussionmentioning

confidence: 85%

Weakening of the Extratropical Storm Tracks in Solar Geoengineering Scenarios

Gertler

O’Gorman

Kravitz

et al. 2020

Geophysical Research Letters

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Solar geoengineering that aims to offset global warming could nonetheless alter atmospheric temperature gradients and humidity and thus affect the extratropical storm tracks. Here, we first analyze climate model simulations from experiment G1 of the Geoengineering Model Intercomparison Project, in which a reduction in incoming solar radiation balances a quadrupling of CO2. The Northern Hemisphere extratropical storm track weakens by a comparable amount in G1 as it does for increased CO2 only. The Southern Hemisphere storm track also weakens in G1, in contrast to a strengthening and poleward shift for increased CO2. Using mean available potential energy, we show that the changes in zonal‐mean temperature and humidity are sufficient to explain the different responses of storm‐track intensity. We also demonstrate similar weakening in a more complex geoengineering scenario. Our results offer insight into how geoengineering affects storm tracks, highlighting the potential for geoengineering to induce novel climate changes.

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“…Some studies have included solaronly GCM runs (e.g., Bala et al, 2008;Schaller et al, 2013Schaller et al, , 2014Modak et al, 2016), but these have included only one or two models, and while some, such as Modak et al (2016), have looked at cloud radiative effects and cloud fraction, none have used methods that account for cloud masking to isolate the radiative effects of physical cloud changes. There is no solar equivalent of abrupt4xCO2 in CMIP5 or any of its associated projects; the closest analogue is probably the aerosol-forcing-only historical runs from the CMIP5 "his-toricalMisc" collection, analyzed, e.g., by Salzmann (2016). The Precipitation Driver and Response Model Intercomparison Project (Myhre et al, 2017) includes a solar constant increase experiment, and the CFMIP component of CMIP6 will include abrupt solar constant increase and decrease runs (Webb et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Besides providing an important theoretical underpinning to the consideration of solar geoengineering scenarios, the G1 experiment is helpful for improving our fundamental understanding of how the climate responds differently to solar forcings, which operate in the shortwave (SW) part of the radiative spectrum versus greenhouse gas forcings, which operate in the longwave (LW), and how linear the response is to combinations of SW and LW forcings. This can help us understand paleoclimates in which the Sun was weaker (Feulner, 2012), attribution of climate change to anthropogenic as opposed to solar forcings (Santer et al, 2003), and the response of the climate to non-solar SW forcings such as aerosol forcings (Salzmann, 2016).…”

mentioning

confidence: 99%

Changes in clouds and thermodynamics under solar geoengineering and implications for required solar reduction

Russotto

Ackerman

2018

Atmos. Chem. Phys.

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Abstract. The amount of solar constant reduction required to offset the global warming from an increase in atmospheric CO2 concentration is an interesting question with implications for assessing the feasibility of solar geoengineering scenarios and for improving our theoretical understanding of Earth's climate response to greenhouse gas and solar forcings. This study investigates this question by analyzing the results of 11 coupled atmosphere–ocean global climate models running experiment G1 of the Geoengineering Model Intercomparison Project, in which CO2 concentrations are abruptly quadrupled and the solar constant is simultaneously reduced by an amount tuned to maintain the top-of-atmosphere energy balance and pre-industrial global mean temperature. The required solar constant reduction in G1 is between 3.2 % and 5.0 %, depending on the model, and is uncorrelated with the models' equilibrium climate sensitivity, while a formula from the experiment specifications based on the models' effective CO2 forcing and planetary albedo is well correlated with but consistently underpredicts the required solar reduction. We propose an explanation for the required solar reduction based on CO2 instantaneous forcing and the sum of radiative adjustments to the combined CO2 and solar forcings. We quantify these radiative adjustments in G1 using established methods and explore changes in atmospheric temperature, humidity, and cloud fraction in order to understand the causes of these radiative adjustments. The zonal mean temperature response in G1 exhibits cooling in the tropics and warming in high latitudes at the surface; greater cooling in the upper troposphere at all latitudes; and stratospheric cooling which is mainly due to the CO2 increase. Tropospheric specific humidity decreases due to the temperature decrease, while stratospheric humidity may increase or decrease depending on the model's temperature change in the tropical tropopause layer. Low cloud fraction decreases in all models in G1, an effect that is robust and widespread across ocean and vegetated land areas. We attribute this to a reduction in boundary layer inversion strength over the ocean, and a reduction in the release of water from plants due to the increased CO2. High cloud fraction increases in the global mean in most models. The low cloud fraction reduction and atmospheric temperature decrease have strong warming effects on the planet, due to reduced reflection of shortwave radiation and reduced emission of longwave radiation, respectively. About 50 % to 75 % of the temperature effect is caused by the stratospheric cooling, while the reduction in atmospheric humidity results in increased outgoing longwave radiation that roughly offsets the tropospheric temperature effect. The longwave (LW) effect of the cloud changes is small in the global mean, despite the increase in high cloud fraction. Taken together, the sum of the diagnosed radiative adjustments and the CO2 instantaneous forcing explains the required solar forcing in G1 to within about 6 %. The cloud fraction response to the G1 experiment raises interesting questions about cloud rapid adjustments and feedbacks under solar versus greenhouse forcings, which would be best explored in a model intercomparison framework with a solar-forcing-only experiment.

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Energy transport, polar amplification, and ITCZ shifts in the GeoMIP G1 ensemble

Cited by 22 publications

References 61 publications

Effects of global warming and solar geoengineering on precipitation seasonality

Effects of global warming and solar geoengineering on precipitation seasonality

Weakening of the Extratropical Storm Tracks in Solar Geoengineering Scenarios

Changes in clouds and thermodynamics under solar geoengineering and implications for required solar reduction

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