Table 2.

Impacts of Control, SRM, and CDR scenarios on ecosystem cycling and chemical environment

	Control	CDR examples			SRM examples
	Doubled atmospheric CO2	Afforestation (land)	Engineered carbon capture and storage (underground)	Ocean fertilization (ocean)	Stratospheric aerosol injection (land/ocean)	Cloud albedo enhancement (ocean)
Effects on nutrient cycling (including nutrient supply to ecosystems)	Elevated CO2: accelerated development of nutrient limitation (Norby et al. 2010); warming: accelerated nutrient cycling, transfer of nutrients from soil to vegetation, accelerated nutrient loss (Melillo et al. 2002); increased nitrogen deposition with fossil fuel use; projected increase in ocean stratification will reduce vertical nutrient supply (Doney 2006)	Increased demand for fertilizer.	Slow reversal of baseline conditions, but no effect on nitrogen deposition	Possible nutrient robbing (Gnanadesikan and Marinov 2008); substantial macronutrient depletion, possibly limited by silicate availability (Boyd et al. 2004); O2 loss in midwater and deep ocean resulting in possible increased hypoxia; reduced surface-ocean and increased deep ocean acidification (Cao and Caldeira 2010)	Changes caused by warming for the “Control” case would be mitigated to some extent; changes caused by elevated CO2 would not be affected
Chemical environment for ecosystems	Potential enhancement of anoxia on continental shelves (Chan et al. 2008)	Increased N2O emissions	Changes for the “Control” case would be mitigated to some extent	O2 loss in deep oceans, acidification in deep oceans (Cao and Caldeira 2010), N2O production (Law 2008)	Some deposition of dilute sulfuric acid but small relative to natural and anthropogenic sources (Kravitz et al. 2009)	Possible increased transport and deposition of sea spray to land