Abstract
Abstract. Sulfate geoengineering has been proposed as an affordable and climate-effective means to temporarily offset the warming produced by the increase of well-mixed greenhouse gases (WMGHGs). This technique would likely have to be applied while and after global intergovernmental measures on emissions of WMGHGs are implemented in order to achieve surface temperature stabilization. The direct radiative effects of sulfur injection in the tropical lower stratosphere can be summarized as increasing shortwave scattering with consequent tropospheric cooling and increasing longwave absorption with stratospheric warming. Indirect radiative effects are related to induced changes in the ozone distribution; stratospheric water vapor abundance,;formation and size of upper-tropospheric cirrus ice particles; and lifetime of long-lived species, namely CH4 in connection with OH changes through several photochemical mechanisms. Direct and indirect effects of sulfate geoengineering both concur to determine the atmospheric response. A review of previous studies on these effects is presented here, with an outline of the important factors that control the amount of sulfur dioxide to be injected in an eventual realization of the experiment. However, we need to take into account that atmospheric models used for these studies have shown a wide range of climate sensitivity and differences in the response to stratospheric volcanic aerosols. In addition, large uncertainties exist in the estimate of some of these aerosol effects.
Highlights
The overwhelming evidence of a surface warming caused by the anthropogenic increase in greenhouse gases (GHGs) has forced the scientific community to look for methods of mitigating and possibly reversing this trend (IPCC, 2007)
While on the one hand these results show that Sulfate geoengineering (SG) leads to the desired effect of offsetting the positive radiative forcing (RF) of increasing well-mixed greenhouse gases (WMGHGs), on the other hand they show that SG effects, such as the lowerstratospheric warming, must be carefully studied
Significant feedback mechanisms exist among the magnitude and location of SO2 injection, aerosol microphysics, background stratospheric dynamics, aerosolinduced surface cooling and stratospheric heating rates, and induced changes in the stratospheric circulation and stratosphere–troposphere exchange
Summary
The overwhelming evidence of a surface warming caused by the anthropogenic increase in greenhouse gases (GHGs) has forced the scientific community to look for methods of mitigating and possibly reversing this trend (IPCC, 2007). Visioni et al.: Sulfate geoengineering posed method to work), affordability, timeliness (how long it would take to deploy it and how fast would it work) and safety (the risks linked with the deployment of the method) Such geoengineering methods would need to be applied while and after global intergovernmental measures on GHG emissions are implemented in order to achieve surface temperature stabilization (Sanderson et al, 2016; Tilmes et al, 2016). The idea itself of sulfate geoengineering comes from the observation of various explosive volcanic eruptions over the last century, which injected large amounts of sulfur in the lower stratosphere over a very short amount of time and whose direct impact on the global mean surface temperature has been known for some time (Robock and Mao, 1995)
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