Abstract
Abstract. Geoengineering has been discussed as a potential option to offset the global impacts of anthropogenic climate change and at the same time reach the global temperature targets of the Paris Agreement. Before any implementation of geoengineering, however, the complex natural responses and consequences of such methods should be fully understood to avoid any unexpected and potentially degrading impacts. Here we assess the changes in ecosystem carbon exchange and storage among different terrestrial biomes under three aerosol-based radiation management methods with the baseline of RCP8.5 using an Earth system model (NorESM1-ME). All three methods used in this study (stratospheric aerosol injection, marine sky brightening, cirrus cloud thinning) target the global mean radiation balance at the top of the atmosphere to reach that of the RCP4.5 scenario. The three radiation management (RM) methods investigated in this study show vastly different precipitation patterns, especially in the tropical forest biome. Precipitation differences from the three RM methods result in large variability in global vegetation carbon uptake and storage. Our findings show that there are unforeseen regional consequences under geoengineering, and these consequences should be taken into account in future climate policies as they have a substantial impact on terrestrial ecosystems. Although changes in temperature and precipitation play a large role in vegetation carbon uptake and storage, our results show that CO2 fertilization also plays a considerable role. We find that the effects of geoengineering on vegetation carbon storage are much smaller than the effects of mitigation under the RCP4.5 scenario (e.g., afforestation in the tropics). Our results emphasize the importance of considering multiple combined effects and responses of land biomes while achieving the global temperature targets of the Paris Agreement.
Highlights
The Paris Agreement, adopted under the Convention of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC) in 2015, aims to limit the temperature increase to 2 ◦C and strive for 1.5 ◦C above pre-industrial levels (UNFCCC, 2015)
Our results suggest that even with reduced temperature stress created by radiation management (RM) applications, the productivity of vegetation in the three most productive biomes on Earth may be reduced due to changing precipitation patterns ( stratospheric aerosol injection (SAI))
We show that the three different RM applications mainly differ in the precipitation patterns, which in turn affect differences in global-scale NPP
Summary
The Paris Agreement, adopted under the Convention of the Parties of the United Nations Framework Convention on Climate Change (UNFCCC) in 2015, aims to limit the temperature increase to 2 ◦C and strive for 1.5 ◦C above pre-industrial levels (UNFCCC, 2015). The benefits of RM methods may be in reducing the current rate of increase in atmospheric temperatures, and in mitigating climate extremes likely caused by warming (Irvine et al, 2019) Despite this encouraging potential, studies have shown numerous undesirable climatic and biophysical side effects of RM, related to sudden termination of RM (e.g., Keller et al, 2014; Lauvset et al, 2017; Lee et al, 2019; Robock et al, 2009; Tjiputra et al, 2016). There is a less studied method referred to as CCT (Gasparini et al, 2020; Mitchell and Finnegan, 2009; Kristjánsson et al, 2015), which aims to cool by letting more longwave radiation escape to space by removing or thinning out highlevel ice clouds (cirrus clouds) This could be done by seeding with aerosols. NorESM is run with a fully interactive prognostic C cycle (i.e., in emission-driven mode)
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