Hi, There was a question a while back about using trees which emit aerosols (isoprene and terpenes) to promote low level clouds. In principle in is a great idea; trees have albedos nearly as low as water, for example the boreal conifer, *picea mariana*, black spruce, has an albedo of 0.09. Gymnosperms generally have albedos betwen that and 0.15. Angiosperms' albedos range from 0.13 to 0.18, with the albedo largely determined by the nitrogen content in the foliage. Fertilised grass and cropland can have albedos between 0.2 and 0.25. Tropical trees have an albedo of around 0.12 to 0.14, and the strongest cooling would be obtained if clouds could be brightened over tropical trees.
Some species within some families of trees produce isoprene (C5H8) in respones to heat and water stress, emissions amounting to about 1 Mt per year. Conifers emit between 0.1 and 0.2 Mt of terpenes, which are also reduced carbon species, and are oxidised to CO2 and H2O in the atmosphere by the same OH radicals which also oxidise methane. This means that if we increased volatile emissions from trees, less methane would get broken down. However, On Mon, Feb 19, 2024 at 10:10 AM <[email protected]> wrote: > [email protected] > <https://groups.google.com/forum/?utm_source=digest&utm_medium=email#!forum/geoengineering/topics> > Google > Groups > <https://groups.google.com/forum/?utm_source=digest&utm_medium=email/#!overview> > <https://groups.google.com/forum/?utm_source=digest&utm_medium=email/#!overview> > Topic digest > View all topics > <https://groups.google.com/forum/?utm_source=digest&utm_medium=email#!forum/geoengineering/topics> > > - Stratospheric Aerosol Injection Geoengineering Would Mitigate > Greenhouse Gas-Induced Drying and Affect Global Drought Patterns > <#m_2118172803418855717_group_thread_0> - 1 Update > > Stratospheric Aerosol Injection Geoengineering Would Mitigate Greenhouse > Gas-Induced Drying and Affect Global Drought Patterns > <http://groups.google.com/group/geoengineering/t/74cff352bb4ba2c0?utm_source=digest&utm_medium=email> > Geoengineering News <[email protected]>: Feb 18 05:52PM +0500 > > *This item and others will be in the monthly “Solar Geoengineering Updates > Substack” newsletter:* https://solargeoengineeringupdates.substack.com/ > ----------------------------------------------------------------- > > https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2023JD039988 > > *Authors* > Zhaochen Liu, Xianmei Lang, Dabang Jiang > > *First published: 07 February 2024* > > https://doi.org/10.1029/2023JD039988 > > *Abstract* > Stratospheric aerosol injection (SAI) is suggested as a potential measure > for alleviating global warming. The potential effects of SAI on global > temperature and precipitation have been extensively discussed, but its > impact on drought has received little attention. Based on the simulations > from the G6sulfur experiment that employs SAI to reduce the global mean > surface temperature from the level of high-tier forcing (Shared > Socioeconomic Pathways SSP5-8.5) scenario to that of medium-tier forcing > (SSP2-4.5) scenario, we investigate the drought response to SAI via the > standardized precipitation evapotranspiration index. During 2081–2100, SAI > effectively offsets the greenhouse gas-induced aridity trend by increasing > the climate water balance at the global scale. Drought duration and > severity decrease but drought frequency increases under SAI forcing. Robust > wetting responses occur over most regions, especially the Sahara, South > America, southern Africa and Australia, while Alaska, Greenland, Southeast > Asia, and tropical Africa face enhanced drought due to SAI. Relative to the > SSP2-4.5 scenario, the regional drying and wetting patterns in G6sulfur are > remarkably different. Notably, in tropical Africa, SAI reverses the wetting > caused by greenhouse gases and induces severer drought. The drought pattern > changes are largely due to evaporative demand alterations caused by the > vapor pressure deficit response. > > *Key Points* > Stratospheric aerosol injection (SAI) would mitigate drought in a high CO2 > emissions scenario with reduced drought duration and severity > > SAI would modify the drought pattern relative to the targeted forcing > scenario, causing particularly severe drought in tropical Africa > > Vapor pressure deficit response plays an important role in the drought > pattern change under SAI forcing > > *Plain Language Summary* > Stratospheric aerosol injection (SAI), by injecting sulfate aerosols into > the stratosphere to scatter part of sunlight back to space, is a proposed > geoengineering method to counteract anthropogenic global warming. Previous > studies have confirmed that SAI can partially offset the climate change > caused by increased greenhouse gas (GHG) concentrations. However, one of > the concerns is that SAI may increase drought risk in some regions. Here, > we have investigated drought response to SAI using simulations from > state-of-the-art climate models. Stratospheric aerosol injection would > effectively mitigate the drought in high GHG forcing scenario globally. The > duration and severity of drought events would decrease over most > landmasses. Meanwhile, the responses of climate water balance to SAI and > GHG are different, causing a dramatic change in drought patterns. Some > regions especially tropical Africa would face severe drying. Such > drought-related regional inequality caused by SAI reminds us to be cautious > when considering geoengineering to counteract climate change. > > *Source: AGU* > Back to top <#m_2118172803418855717_digest_top> > You received this digest because you're subscribed to updates for this > group. 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