Response to marine cloud brightening in a multi-model ensemble

Stjern, CW; Muri, Helene; Ahlm, Lars; Boucher, Oliviér; Cole, Jason N. S.; Ji, Duan; Jones, Andrew S.; Haywood, Jim; Kravitz, Ben; Lenton, Andrew; Moore, J.D.; Niemeier, Ulrike; Phipps, Steven J.; Schmidt, Henry; Watanabe, Shingo; Kristjánsson, JE

doi:10.5194/acp-2017-629

Cited by 8 publications

(12 citation statements)

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“…On the other hand, enhanced ascent over, for example, Africa, northern South America, and in the South Pacific Convergence Zone coincides with increased cloud water path and precipitation. These patterns of enhanced cloud water, precipitation, and atmospheric upward motion over low-latitude continents combined with reduced cloud water, precipitation, and ascent over some lowlatitude ocean regions have been reported previously by Bala et al (2011), , , Crook et al (2015), and Stjern et al (2017). This is a result of reduced absorption of solar radiation over ocean where sea salt concentrations are elevated while continental regions are left less affected, increasing the land-sea gradient over the tropics.…”

Section: Change In Sea Salt Concentrations Cloud Properties and Atmmentioning

confidence: 75%

Marine cloud brightening – as effective without clouds

et al. 2017

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Abstract. Marine cloud brightening through sea spray injection has been proposed as a climate engineering method for avoiding the most severe consequences of global warming. A limitation of most of the previous modelling studies on marine cloud brightening is that they have either considered individual models or only investigated the effects of a specific increase in the number of cloud droplets. Here we present results from coordinated simulations with three Earth system models (ESMs) participating in the Geoengineering Model Intercomparison Project (GeoMIP) G4sea-salt experiment. Injection rates of accumulation-mode sea spray aerosol particles over ocean between 30 • N and 30 • S are set in each model to generate a global-mean effective radiative forcing (ERF) of −2.0 W m −2 at the top of the atmosphere. We find that the injection increases the cloud droplet number concentration in lower layers, reduces the cloud-top effective droplet radius, and increases the cloud optical depth over the injection area. We also find, however, that the global-mean clear-sky ERF by the injected particles is as large as the corresponding total ERF in all three ESMs, indicating a large potential of the aerosol direct effect in regions of low cloudiness. The largest enhancement in ERF due to the presence of clouds occur as expected in the subtropical stratocumulus regions off the west coasts of the American and African continents. However, outside these regions, the ERF is in general equally large in cloudy and clear-sky conditions. These findings suggest a more important role of the aerosol direct effect in sea spray climate engineering than previously thought.

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Section: Change In Sea Salt Concentrations Cloud Properties and Atmmentioning

confidence: 75%

Marine cloud brightening – as effective without clouds

et al. 2017

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“…2e). The tropical and subtropical changes in SST with MSB are linked to an enhancement of the Pacific Walker cell, which is induced when MSB is applied as has been found in previous studies such as Bala et al (2011), Alterskjaer et al (2013), , Stjern et al (2017), and Muri et al (2017).…”

Section: Global Changes In Ocean Temperature and Oxygen Concentrationmentioning

confidence: 84%

“…Partanen et al (2016) furthermore prescribe their forcing in terms of changes to the radiation, and hence miss out on further feedbacks with their one-layered atmosphere with prescribed circulation, which are processes that are much more comprehensively represented in our fully coupled Earth system model. MSB may, for example, lead to an increased sinking of air over the oceans and hence a reduction in cloud cover, as seen in Ahlm et al (2017), Stjern et al (2017), and . The ecosystem module in NorESM1-ME is not substantially more complex than that of the UViC ESCM model, but differences could arise due to better representation of the ocean physical circulation (owing to higher spatial resolution) and air-sea interactions.…”

Section: Comparison With Previous Studiesmentioning

confidence: 99%

Climate engineering and the ocean: effects on biogeochemistry and primary production

2017

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Abstract. Here we use an Earth system model with interactive biogeochemistry to project future ocean biogeochemistry impacts from the large-scale deployment of three different radiation management (RM) climate engineering (also known as geoengineering) methods: stratospheric aerosol injection (SAI), marine sky brightening (MSB), and cirrus cloud thinning (CCT). We apply RM such that the change in radiative forcing in the RCP8.5 emission scenario is reduced to the change in radiative forcing in the RCP4.5 scenario. The resulting global mean sea surface temperatures in the RM experiments are comparable to those in RCP4.5, but there are regional differences. The forcing from MSB, for example, is applied over the oceans, so the cooling of the ocean is in some regions stronger for this method of RM than for the others. Changes in ocean net primary production (NPP) are much more variable, but SAI and MSB give a global decrease comparable to RCP4.5 ( ∼ 6 % in 2100 relative to , while CCT gives a much smaller global decrease of ∼ 3 %. Depending on the RM methods, the spatially inhomogeneous changes in ocean NPP are related to the simulated spatial change in the NPP drivers (incoming radiation, temperature, availability of nutrients, and phytoplankton biomass) but mostly dominated by the circulation changes. In general, the SAI-and MSB-induced changes are largest in the low latitudes, while the CCT-induced changes tend to be the weakest of the three. The results of this work underscore the complexity of climate impacts on NPP and highlight the fact that changes are driven by an integrated effect of multiple environmental drivers, which all change in different ways. These results stress the uncertain changes to ocean productivity in the future and advocate caution at any deliberate attempt at large-scale perturbation of the Earth system.

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“…Numerical models can be used to investigate the feasibility and cost of environmental interventions before trials are undertaken. This is a necessity for global scale geo-engineering proposals [ 9 , 11 ] which would never be considered without a highly credible model representation of the impact of the intervention. Numerical modelling is equally important for more localised interventions [ 12 ] in order to obtain the most cost effective application of the intervention.…”

Section: Introductionmentioning

confidence: 99%

Optimising cool-water injections to reduce thermal stress on coral reefs of the Great Barrier Reef

et al. 2020

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Coral bleaching driven by ocean warming is one of the most visible ecological impacts of climate change and perhaps the greatest threat to the persistence of reefs in the coming decades. In the absence of returning atmospheric greenhouse gas concentrations to those compatible with ocean temperatures below the mass coral bleaching temperature thresholds, the most straightforward means to reduce thermal-stress induced bleaching is to cool water at the seabed. The feasibility of reducing the seabed temperature through cool-water injections is considered first by analysing the feasibility of doing so on 19 reefs with differing physical environments using a simple residence time metric in 200 m resolution hydrodynamic model configurations. We then concentrate on the reefs around Lizard Island, the most promising candidate of the 19 locations, and develop a 40 m hydrodynamic model to investigate the effect of the injection of cool water at differing volumetric rates. Injecting 27˚C seawater at a rate of 5 m 3 s −1 at 4 sites in early 2017 cooled 97 ha of the reef by 0.15˚C or more. The power required to pump 5 m 3 s −1 through a set of pipes over a distance of 3 km from a nearby channel is *466 kW. This power applied at 4 sites for 3 months achieves a 2 Degree Heating Weeks (DHWs) reduction on 97 ha of reef. A more precise energy costing will require further expert engineering design of the pumping equipment and energy sources. Even for the most physically favourable reefs, cool-water transported through pipes and injected at a reef site is energy expensive and cannot be scaled up to any meaningful fraction of the 3,100 reefs of the GBR. Should priority be given to reducing thermal stress on one or a few high value reefs, this paper provides a framework to identify the most promising sites.

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Response to marine cloud brightening in a multi-model ensemble

Cited by 8 publications

References 0 publications

Marine cloud brightening – as effective without clouds

Marine cloud brightening – as effective without clouds

Climate engineering and the ocean: effects on biogeochemistry and primary production

Optimising cool-water injections to reduce thermal stress on coral reefs of the Great Barrier Reef

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