Hemispherically symmetric strategies for stratospheric aerosol injection

Journal Article · Wed Mar 13 00:00:00 EDT 2024 · Earth System Dynamics (Online)

DOI:https://doi.org/10.5194/esd-15-191-2024· OSTI ID:2429494

Zhang, Yan ^[1]; MacMartin, Douglas G. ^[1]; Visioni, Daniele ^[1]; Bednarz, Ewa M. ^[2]; Kravitz, Ben ^[3]

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1. Cornell Univ., Ithaca, NY (United States)
2. Cornell Univ., Ithaca, NY (United States); Univ. of Colorado, Boulder, CO (United States); National Oceanic and Atmospheric Administration (NOAA), Boulder, CO (United States). NOAA Chemical Sciences Laboratory (CSL)
3. Indiana Univ., Bloomington, IN (United States); Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Stratospheric aerosol injection (SAI) comes with a wide range of possible design choices, such as the location and timing of the injection. Different stratospheric aerosol injection strategies can yield different climate responses; therefore, understanding the range of possible climate outcomes is crucial to making informed future decisions on SAI, along with the consideration of other factors. Yet, to date, there has been no systematic exploration of a broad range of SAI strategies. This limits the ability to determine which effects are robust across different strategies and which depend on specific injection choices. This study systematically explores how the choice of SAI strategy affects climate responses in one climate model. Here, we introduce four hemispherically symmetric injection strategies, all of which are designed to maintain the same global mean surface temperature: an annual injection at the Equator (EQ), an annual injection of equal amounts of SO₂ at 15° N and 15° S (15N+15S), an annual injection of equal amounts of SO₂ at 30° N and 30° S (30N+30S), and a polar injection strategy that injects equal amounts of SO₂ at 60° N and 60° S only during spring in each hemisphere (60N+60S). We compare these four hemispherically symmetric SAI strategies with a more complex injection strategy that injects different quantities of SO₂ at 30° N, 15° N, 15° S, and 30° S in order to maintain not only the global mean surface temperature but also its large-scale horizontal gradients. All five strategies are simulated using version 2 of the Community Earth System Model with the middle atmosphere version of the Whole Atmosphere Community Climate model, version 6, as the atmospheric component, CESM2(WACCM6-MA), with the global warming scenario, Shared Socioeconomic Pathway (SSP)2-4.5. We find that the choice of SAI strategy affects the spatial distribution of aerosol optical depths, injection efficiency, and various surface climate responses. In addition, injecting in the subtropics produces more global cooling per unit injection, with the EQ and the 60N+60S cases requiring, respectively, 59 % and 50 % more injection than the 30N+30S case to meet the same global mean temperature target. Injecting at higher latitudes results in larger Equator-to-pole temperature gradients. While all five strategies restore Arctic September sea ice, the high-latitude injection strategy is more effective due to the SAI-induced cooling occurring preferentially at higher latitudes. These results suggest trade-offs wherein different strategies appear better or worse, depending on which metrics are deemed important.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 2429494
• Report Number(s): PNNL-SA--201515
• Journal Information: Earth System Dynamics (Online), Journal Name: Earth System Dynamics (Online) Journal Issue: 2 Vol. 15; ISSN 2190-4987
• Publisher: Copernicus Publications, EGU
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES