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

Abstract

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.

Impact of Solar Radiation Modification on Allowable CO2 Emissions: What Can We Learn From Multimodel Simulations?

“…However, recent studies such as Eliseev (2012) or Keith et al (2017) suggest that SRM might be understood as a form of carbon dioxide removal (CDR) technique because of its impacts on the global carbon cycle. This statement is also supported by former studies (Eliseev, 2012;Govindasamy et al, 2002;Keller et al, 2014;Lauvset et al, 2017;Matthews & Caldeira, 2007;Muri et al, 2015;Sonntag et al, 2018) which suggest that SRM is likely to strengthen carbon uptake by both ocean and terrestrial ecosystems. This finding is also supported by the modeled response of the carbon cycle to major volcanic eruptions (Brovkin et al, 2010;MacMartin et al, 2016;Rothenberg et al, 2012;Tjiputra & Otterå, 2011).…”

The Response of Permafrost and High‐Latitude Ecosystems Under Large‐Scale Stratospheric Aerosol Injection and Its Termination

“…Recent studies investigating the impacts of SAI on global and regional climate (e.g., Berdahl et al, 2014;Kravitz et al, 2015;Muri et al, 2018) suggest that the overall effect of SAI is the amelioration of global-scale warming by reducing the incoming shortwave radiation. Therefore, there are large impacts on land and ocean carbon cycling on a global scale (Lauvset et al, 2017;Muri et al, 2018;Tjiputra et al, 2016). Our previous study using SAI method showed that global mean surface temperature can be reduced by 2°C by the year 2100 and 5°C by the year 2200 compared to its baseline RCP8.5 scenario (Tjiputra et al, 2016).…”

Inequal Responses of Drylands to Radiative Forcing Geoengineering Methods

“…However, unequal responses of drylands to individual RFG methodologies are substantial over CNA, WSH, and AUS. The cooling over the ocean surface by the MSB leads to bimodal patterns between tropical and subtropical North Pacific (Lauvset et al, 2017). When CCT is implemented, thinner cirrus clouds increase incoming solar radiation and strengthens radiative cooling in the upper troposphere.…”

“…Also, the warming in lower troposphere and cooling in upper troposphere promote convections and enhance the global hydrological cycle (Kristjánsson et al, 2015). The cooling over the ocean surface by the MSB leads to bimodal patterns between tropical and subtropical North Pacific (Lauvset et al, 2017). These changes enhance convective activities over the western Pacific and eastern Indian Ocean, which alters the Pacific Walker circulation similarly to that under a La Ninã event (Niemeier et al, 2013;Stjern et al, 2018).…”