Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

Nalam, Aditya; Bala, Govindasamy; Modak, Angshuman

doi:10.1007/s00382-017-3810-y

Cited by 36 publications

(69 citation statements)

References 65 publications

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“…The mass of aerosol was chosen based on Nalam et al (2017), where they prescribed 20 Tg of background sulfate aerosols in five layers centered at 37 hPa to offset the global mean surface temperature change caused by a doubling of CO 2 . In CAM4, the sulfate aerosols are log-normally distributed with fixed size distributions (Neale et al, 2010). For our stratospheric aerosol experiments, we use volcanic aerosols which have an effective mean radius of 0.426 µm and a geometric standard deviation of 1.25.…”

Section: Experimental Designmentioning

confidence: 99%

“…For our stratospheric aerosol experiments, we use volcanic aerosols which have an effective mean radius of 0.426 µm and a geometric standard deviation of 1.25. The mass of the aerosols consists of 75 % H 2 SO 4 and 25 % H 2 O (Neale et al, 2010). The zonal variations as well as interannual variations (for this study) in mixing ratio of the volcanic aerosols are omitted (Ammann et al, 2003;Neale et al, 2010).…”

Section: Experimental Designmentioning

confidence: 99%

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Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

et al. 2019

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Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer. In this study, we isolate and assess the sensitivity of stratospheric aerosol radiative forcing and the resulting climate change to the altitude of the aerosol layer. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability, and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of the amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with the altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have higher stratospheric residence time; these two effects are likely to be of comparable importance.

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Section: Experimental Designmentioning

confidence: 99%

Section: Experimental Designmentioning

confidence: 99%

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

et al. 2019

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“…It is defined as the median latitude of zonal mean area-weighted precipitation between 20°S and 20°N. In order to identify small shifts in the ITCZ position, we interpolate the ∼2°latitude grid in to a 0.01°grid (Donohoe et al 2013, Devaraju et al 2015, Nalam et al 2018.…”

Section: How Much Does the Itcz Shifts?mentioning

confidence: 99%

“…We also estimate the corresponding annual mean northward heat transport (Donohoe et al 2013, Nalam et al 2018 in the 60×BC case (figure S14). We find that for a ∼7°shift in the ITCZ position, the magnitude of annual mean cross-equatorial atmospheric northward heat transport (AHTeq) to the SH from the NH is ∼−1.2 PW.…”

Section: How Much Does the Itcz Shifts?mentioning

confidence: 99%

Efficacy of black carbon aerosols: the role of shortwave cloud feedback

Modak

Bala

2019

Environ. Res. Lett.

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Using idealized climate model simulations, we investigate the effectiveness of black carbon (BC) aerosols in warming the planet relative to CO 2 forcing. We find that a 60-fold increase in the BC aerosol mixing ratio from the present-day levels leads to the same equilibrium global mean surface warming (∼4.1 K) as for a doubling of atmospheric CO 2 concentration. However, the radiative forcing is larger (∼5.5 Wm −2 ) in the BC case relative to the doubled CO 2 case (∼3.8 Wm −2 ) for the same surface warming indicating the efficacy (a metric for measuring the effectiveness) of BC aerosols to be less than CO 2 . The lower efficacy of BC aerosols is related to the differences in the shortwave (SW) cloud feedback: negative in the BC case but positive in the CO 2 case. In the BC case, the negative SW cloud feedback is related to an increase in the tropical low clouds which is associated with a northward shift (∼7°) of the Intertropical Convergence Zone (ITCZ). Further, we show that in the BC case fast precipitation suppression offsets the surface temperature mediated precipitation response and causes ∼8% net decline in the global mean precipitation. Our study suggests that a feedback between the location of ITCZ and the interhemispheric temperature could exist, and the consequent SW cloud feedback could be contributing to the lower efficacy of BC aerosols. Therefore, an improved representation of low clouds in climate models is likely the key to understand the global climate sensitivity to BC aerosols.

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“…Studies have shown that the addition of sulfate aerosols into the stratosphere could offset the CO 2 -induced global mean warming but usually at the cost of a reduced intensity of global hydrological cycle mainly associated with the fast climate adjustments (e.g., Duan et al, 2018;Ferraro & Griffiths, 2016;Kalidindi et al, 2015;Myhre et al, 2018). Also, stratospheric aerosol geoengineering can induce changes in stratospheric ozone concentration and large-scale stratospheric circulation due to the change in stratospheric temperature, water vapor content, and heating rate (Ferraro et al, 2015;Kalidindi et al, 2015;Krishna-Pillai Sukumara-Pillai et al, 2019;Madronich et al, 2018;Nalam et al, 2017;Pitari et al, 2014;Richter et al, 2017;Simone Tilmes et al, 2009). A number of recent studies have shown that multiple temperature goals could be achieved by interactively adjusting the location and rate of sulfate aerosol injections, indicating the possibility to achieve multiple regional climate mitigation goals (e.g., Kravitz the climate response, SAI geoengineering has been simulated with multiple climate models using the same experimental protocol under the framework of the Geoengineering Model Intercomparison Project (e.g., Kravitz et al, 2011Kravitz et al, , 2015.…”

Section: Introductionmentioning

confidence: 99%

Climate Response to Pulse Versus Sustained Stratospheric Aerosol Forcing

Duan

Cao

Bala

et al. 2019

Geophysical Research Letters

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Solar geoengineering has been suggested as a potential means to counteract anthropogenic warming. Major volcanic eruptions have been used as natural analogues to large‐scale deployments of stratospheric aerosol geoengineering, yet difference in climate responses to these forcings remains unclear. Using the National Center for Atmospheric Research Community Earth System Model, we compare climate responses to two highly idealized stratospheric aerosol forcings that have different durations: a short‐term pulse representative of volcanic eruptions and a long‐term sustained forcing representative of geoengineering. For the same amount of global mean cooling, decreases in land temperature, precipitation, and runoff in the pulse case are much larger than that in the sustained case. The spatial pattern changes differ substantially between these two cases. Thus, direct extrapolations from volcanic eruption observations provide limited insight into impacts of potential stratospheric aerosol geoengineering. However, simulations of volcanic eruptions can be useful to test process representations in models that are used to simulate geoengineering deployments.

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Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

Cited by 36 publications

References 65 publications

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

Climate system response to stratospheric sulfate aerosols: sensitivity to altitude of aerosol layer

Efficacy of black carbon aerosols: the role of shortwave cloud feedback

Climate Response to Pulse Versus Sustained Stratospheric Aerosol Forcing

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