A Model‐Based Investigation of Terrestrial Plant Carbon Uptake Response to Four Radiation Modification Approaches

Abstract

A number of radiation modification approaches have been proposed to counteract anthropogenic warming by intentionally altering Earth's shortwave or longwave fluxes. While several previous studies have examined the climate effect of different radiation modification approaches, only a few have investigated the carbon cycle response. Our study examines the response of plant carbon uptake to four radiation modification approaches that are used to offset the global mean warming caused by a doubling of atmospheric CO 2 . Using the National Center for Atmospheric Research Community Earth System Model, we performed simulations that represent four idealized radiation modification options: solar constant reduction, sulfate aerosol increase (SAI), marine cloud brightening, and cirrus cloud thinning (CCT). Relative to the high CO 2 state, all these approaches reduce gross primary production (GPP) and net primary production (NPP). In high latitudes, decrease in GPP is mainly due to the reduced plant growing season length, and in low latitudes, decrease in GPP is mainly caused by the enhanced nitrogen limitation due to surface cooling. The simulated GPP for sunlit leaves decreases for all approaches. Decrease in sunlit GPP is the largest for SAI which substantially decreases direct sunlight, and the smallest for CCT, which increases direct sunlight that reaches the land surface. GPP for shaded leaves increases in SAI associated with a substantial increase in surface diffuse sunlight, and decreases in all other cases. The combined effects of CO 2 increase and radiation modification result in increases in primary production, indicating the dominant role of the CO 2 fertilization effect on plant carbon uptake.Plain Language Summary A number of radiation modification approaches have been proposed to intentionally alter Earth's radiation balance to counteract anthropogenic warming. However, only a few studies have analyzed the potential impact of these approaches on the terrestrial plant carbon cycle. Here, we simulate four idealized radiation modification approaches, which include direct reduction of incoming solar radiation, increase in stratospheric sulfate aerosols concentration, enhancement of marine low cloud albedo, and decrease in high-level cirrus cloud cover, and analyze changes in plant photosynthesis and respiration. The first three approaches cool the earth by reducing incoming solar radiation, and the last approach allows more outgoing thermal radiation. These approaches are designed to offset the global mean warming caused by doubled atmospheric CO 2 . Compared to the high CO 2 world, all approaches will limit plant growth due to induced surface cooling in high latitudes and will lead to reduced nitrogen supply in low latitudes, leading to an overall reduction in the plant carbon uptake over land. Different approaches also produce different changes in surface direct and diffuse sunlight, which has important implications for plant photosynthesis. Relative to the unperturbed climate, the combined effects of enhanced CO...

Overlooked Long‐Term Atmospheric Chemical Feedbacks Alter the Impact of Solar Geoengineering: Implications for Tropospheric Oxidative Capacity

“…Prior studies of the impact of SAI on terrestrial GPP and crop yields, none of which have included the impact of changes in surface ozone but rather focused on changes in climate and radiation available for photosynthesis, have large disagreements in the magnitude and sometimes sign of the impact. Available estimates for the impact of SAI on terrestrial GPP range from a 3.8 Gt C yr −1 increase to a 14.7 C yr −1 decrease (Duan et al., 2020; Xia et al., 2016; Yang et al., 2020), and from a ∼0% change to ∼10% increase for the impact on global crop yields (Fan et al., 2021; Proctor et al., 2018). With regards to acid rain and acid deposition, we find minimal net changes due to chemical feedbacks.…”

“…For example, SAI induced changes in the hydrological cycle could affect both OH production and cloud chemistry rates, all with implications for the net radiative response (Tilmes et al, 2013;Visioni et al, 2017). Other examples include the impacts of SAI on ecosystems and biogenic VOC emissions (Duan et al, 2020;Telford et al, 2010;Xia et al, 2016;Yang et al, 2020) and on stratospheric water vapor. The use of a coupled chemistry-climate model or full Earth System model is also needed to fully characterize the relationship between changes to instantaneous radiative forcing from SAI and the associated chemical feedbacks and ultimate climate response (Szopa et al, 2021).…”

Regional Response of Land Hydrology and Carbon Uptake to Different Amounts of Solar Radiation Modification

“…While the amount of SRM increases, increased surface cooling tends to suppress plant growth. At high latitudes, the suppression of plant growth is mainly associated with reduced growing season (Glienke et al., 2015), whereas at low latitudes, the suppression of plant growth is mainly associated with reduced nitrogen remineralization and availability (Duan et al., 2020). A stronger SRM also leads to a larger reduction in direct sunlight that decreases carbon uptake for sunlit leaves.…”

Climate Response to Latitudinal and Altitudinal Distribution of Stratospheric Sulfate Aerosols

“…As shown in Figure 6e, sunlit gross primary productivity (GPP) decreases across all latitudes. The reduction of sunlit GPP at high latitudes is mainly associated with suppression of plant growth due to surface cooling, and the reduction of sunlit GPP at low latitudes is mainly associated with the reduction of the nitrogen remineralization rate caused by cooling that reduces nitrogen availability in the soil (Duan et al, 2020). Reduction in direct sunlight reaching the surface further contributes to the decrease in sunlit GPP.…”