The cost of stratospheric climate engineering revisited

Abstract. The injection of sulfur dioxide (SO 2 ) into the stratosphere to form an artificial stratospheric aerosol layer is discussed as an option for solar radiation management. Sulfate aerosol scatters solar radiation and absorbs infrared radiation, which warms the stratospheric sulfur layer. Simulations with the general circulation model ECHAM5-HAM, including aerosol microphysics, show consequences of this warming, including changes of the quasi-biennial oscillation (QBO) in the tropics. The QBO slows down after an injection of 4 Tg(S) yr −1 and completely shuts down after an injection of 8 Tg(S) yr −1 . Transport of species in the tropics and subtropics depends on the phase of the QBO. Consequently, the heated aerosol layer not only impacts the oscillation of the QBO but also the meridional transport of the sulfate aerosols. The stronger the injection, the stronger the heating and the simulated impact on the QBO and equatorial wind systems. With increasing injection rate the velocity of the equatorial jet streams increases, and the less sulfate is transported out of the tropics. This reduces the global distribution of sulfate and decreases the radiative forcing efficiency of the aerosol layer by 10 to 14 % compared to simulations with low vertical resolution and without generated QBO. Increasing the height of the injection increases the radiative forcing only for injection rates below 10 Tg(S) yr −1 (8-18 %), a much smaller value than the 50 % calculated previously. Stronger injection rates at higher levels even result in smaller forcing than the injections at lower levels.

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“…Estimates of lifting costs of sulfur into the stratosphere (e.g. Moriyama et al, 2016) depend strongly on the efficiency of the injection.…”

Section: Discussionmentioning

confidence: 99%

“…The efficiency even decreases for strong injection rates of 20 Tg(S) yr −1 and more as a consequence of the strong tropical confinement in the high injection cases. This result challenges an injection at 30 hPa at the equator, because, additionally, it is technically much more demanding (Moriyama et al, 2016).…”

Section: Effects On Radiative Forcingmentioning

confidence: 99%

Changing transport processes in the stratosphere by radiative heating of sulfate aerosols

2017

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“…Anyway, when comparing the SG techniques to others, it still appears to be one of the most feasible, taking into account its relatively high level of effectiveness and affordability (Robock et al, 2009;McClellan et al, 2012). However, higher estimates on the SG costs have also been reported in the recent literature (Moriyama et al, 2016), raising doubts about its affordability.…”

Section: Discussionmentioning

confidence: 99%

Sulfate geoengineering: a review of the factors controlling the needed injection of sulfur dioxide

2017

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Abstract. Sulfate geoengineering has been proposed as an affordable and climate-effective means to temporarily offset the warming produced by the increase of well-mixed greenhouse gases (WMGHGs). This technique would likely have to be applied while and after global intergovernmental measures on emissions of WMGHGs are implemented in order to achieve surface temperature stabilization. The direct radiative effects of sulfur injection in the tropical lower stratosphere can be summarized as increasing shortwave scattering with consequent tropospheric cooling and increasing longwave absorption with stratospheric warming. Indirect radiative effects are related to induced changes in the ozone distribution; stratospheric water vapor abundance,;formation and size of upper-tropospheric cirrus ice particles; and lifetime of long-lived species, namely CH 4 in connection with OH changes through several photochemical mechanisms. Direct and indirect effects of sulfate geoengineering both concur to determine the atmospheric response. A review of previous studies on these effects is presented here, with an outline of the important factors that control the amount of sulfur dioxide to be injected in an eventual realization of the experiment. However, we need to take into account that atmospheric models used for these studies have shown a wide range of climate sensitivity and differences in the response to stratospheric volcanic aerosols. In addition, large uncertainties exist in the estimate of some of these aerosol effects.

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“…Releasing a few teragrams of material per year into the lower tropical stratosphere (∼ 20 km) would produce an aerosol layer with global coverage. Multiple, independent feasibility assessments of the proposal conclude that this could be achieved at a cost of the order of USD 1 billion per teragram using high-altitude jets (McClellan et al, 2012;Moriyama et al, 2016;Robock et al, 2009 . For this reason, here we focus on stratospheric aerosol injection and unless otherwise stated, solar geoengineering will hereafter refer to stratospheric aerosol geoengineering only.…”

Section: Future Sea Level Rise and The Potential Of Solar Geoengineeringmentioning

confidence: 99%

Brief communication: Understanding solar geoengineering's potential to limit sea level rise requires attention from cryosphere experts

2018

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Abstract. Stratospheric aerosol geoengineering, a form of solar geoengineering, is a proposal to add a reflective layer of aerosol to the stratosphere to reduce net radiative forcing and so to reduce the risks of climate change. The efficacy of solar geoengineering at reducing changes to the cryosphere is uncertain; solar geoengineering could reduce temperatures and so slow melt, but its ability to reverse ice sheet collapse once initiated may be limited. Here we review the literature on solar geoengineering and the cryosphere and identify the key uncertainties that research could address. Solar geoengineering may be more effective at reducing surface melt than a reduction in greenhouse forcing that produces the same global-average temperature response. Studies of natural analogues and model simulations support this conclusion. However, changes below the surfaces of the ocean and ice sheets may strongly limit the potential of solar geoengineering to reduce the retreat of marine glaciers. High-quality process model studies may illuminate these issues. Solar geoengineering is a contentious emerging issue in climate policy and it is critical that the potential, limits, and risks of these proposals are made clear for policy makers.

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The cost of stratospheric climate engineering revisited

Cited by 51 publications

References 51 publications

Changing transport processes in the stratosphere by radiative heating of sulfate aerosols

Changing transport processes in the stratosphere by radiative heating of sulfate aerosols

Sulfate geoengineering: a review of the factors controlling the needed injection of sulfur dioxide

Brief communication: Understanding solar geoengineering's potential to limit sea level rise requires attention from cryosphere experts

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