Designing a Radiative Antidote to CO2. Issue 1 (12th January 2021)

• Record Type: Journal Article
• Authors: Seeley, Jacob T.; Lutsko, Nicholas J.; Keith, David W.
• Is Part Of: Geophysical research letters. Volume 48:Issue 1(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-01-12
• Subjects: CO2 forcing -- hydrological cycle -- idealized models -- radiative transfer -- solar geoengineering -- solar radiation modification; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL090876
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Solar radiation modification (SRM) reduces the CO2 ‐induced change to the mean global hydrological cycle disproportionately more than it reduces the CO2 ‐induced increase in mean surface temperature. Thus, if SRM were used to offset all CO2 ‐induced mean warming, global‐mean precipitation would be less than in an unperturbed climate. Here, we show that the mismatch between the mean hydrological effects of CO2 and SRM may partly be alleviated by spectrally tuning the SRM intervention (reducing insolation at some wavelengths more than others). By concentrating solar dimming at near‐infrared wavelengths, where H2 O has strong absorption bands, the direct effect of CO2 on the tropospheric energy budget can be offset, which minimizes perturbations to the mean hydrological cycle. Idealized cloud‐resolving simulations of radiative‐convective equilibrium confirm that spectrally tuned SRM can simultaneously maintain mean surface temperature and precipitation at their unperturbed values even as large quantities of CO2 are added to the atmosphere. Plain Language Summary: It may be possible to partly counteract CO2 ‐driven climate change by solar radiation modification (SRM) that intentionally reduces the amount of sunlight absorbed by the Earth. But different wavelengths of the solar spectrum are absorbed at different altitudes within the surface‐atmosphere system, so different climatic effects are to be expected depending on which wavelengths of sunlight are affected by an SRM intervention. Here, we show that if the goal is to minimize perturbations to the mean hydrological cycle, the ideal spectrally tuned SRM intervention may need to focus on near‐infrared wavelengths. This study clarifies the basic physics underlying the effects of SRM on atmospheric energetics and the mean hydrological cycle. Key Points: Spectrally flat solar geoengineering reduces CO2 ‐induced change in mean rainfall disproportionately more than mean temperature A spectrally tuned sunshade restores mean temperature and rainfall simultaneously in an idealized model Emerging technologies could preferentially scatter sunlight in the near‐infrared, providing a spectral sunshade