Poster's note: this has the opposite sign to other work on the subject eg https://keith.seas.harvard.edu/publications/solar-geoengineering-reduces-atmospheric-carbon-burden
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JD031883 Journal of Geophysical Research: AtmospheresVolume 125, Issue 9 Research Article A Model‐Based Investigation of Terrestrial Plant Carbon Uptake Response to Four Radiation Modification Approaches Lei Duan Long Cao Govindasamy Bala Ken Caldeira First published:04 April 2020 https://doi.org/10.1029/2019JD031883 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 CO2. 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 CO2 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 CO2 increase and radiation modification result in increases in primary production, indicating the dominant role of the CO2 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 CO2. Compared to the high CO2 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 CO2 and radiation modifications leads to an increase in plants' primary production. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/CAJ3C-04U16sw-Z9QCLEVXqs5Z0r0MRzGN0dfr-A8%2By_eaaYiag%40mail.gmail.com.
