Climate tipping points and solar geoengineering

Abstract

We study optimal climate policy when climate tipping points and solar geoengineering are present. Solar geoengineering reduces temperatures without reducing greenhouse gas emissions. Climate tipping points are irreversible and uncertain events that cause large damages. We analyze three different rules related to the availability of solar geoengineering: a ban, using solar geoengineering as insurance against the risk of tipping points, or using solar geoengineering only as remediation in the aftermath of a tipping point. We model three distinct types of tipping points: two that alter the climate system and one that yields a direct economic cost. Using an analytic model, we find that an optimal policy, which minimizes expected losses from the tipping point, includes both emissions reductions and solar geoengineering from the onset.Using a numerical simulation model, we quantify optimal policy and various outcomes under the alternative scenarios. The presence of tipping points leads to more mitigation and more solar geoengineering use and lower temperatures. * We thank Derek Lemoine and seminar participants at Tennessee, Stanford, Harvard, and the Southern Economic Association annual meeting for comments.

Complementing CO<sub>2</sub> emission reduction by solar radiation management might strongly enhance future welfare

“…The damages associated with the annual sulfur injections needed to offset a warming of 2.5 K are assumed to equal 20 % of the standard case damage. Previous studies (Heutel et al, 2016(Heutel et al, , 2018 likewise split the damage function, but without including residual climate change (P ). Heutel et al (2018) assume oceanic and atmospheric CO 2 to cause 10 % of the total damage each (20 % in total).…”

“…Previous studies (Heutel et al, 2016(Heutel et al, , 2018 likewise split the damage function, but without including residual climate change (P ). Heutel et al (2018) assume oceanic and atmospheric CO 2 to cause 10 % of the total damage each (20 % in total). However, atmospheric CO 2 is not known to cause substantial direct damage and may even be beneficial to plant growth (Ciais et al, 2013), while oceanic CO 2 leads to ocean acidification.…”

“…However, atmospheric CO 2 is not known to cause substantial direct damage and may even be beneficial to plant growth (Ciais et al, 2013), while oceanic CO 2 leads to ocean acidification. As mentioned, we do not explicitly compute oceanic CO 2 but reduce total CO 2 -related damage to 10 % because half of the total damage in Heutel et al (2018) seems in fact small. The splitting between T and P is somewhat arbitrary, but is based on the rough assumption that, although precipitation changes can have a substantial impact, much of the damage is either determined by temperature (especially sea level rise, a major contributor) or at least strongly influenced by it (e.g.…”

“…Here we build on earlier studies, which often included uncertainty only through parameter sensitivity analysis (Goes et al, 2011;Bahn et al, 2015) or as a simplified two-step decision problem (Moreno-Cruz and Keith, 2013). Two recent studies (Heutel et al, 2016(Heutel et al, , 2018 include climate tipping behaviour and parameter uncertainty in DICE but employ a simple four-step look-ahead scheme that is unsuitable for long-term optimisation. We employ dynamic programming (Bellman, 1957) to perform the first rigorous costbenefit analysis of SRM under uncertainty, albeit with a simple model.…”

Challenges and Opportunities for Integrated Modeling of Climate Engineering

“…On the other hand, SRM has been predominantly assessed by small-scale models such as DICE [28][29][30][31] , with few exceptions 32 . Modeling SRM technologies is not particularly complicated, in terms of costs and effectiveness 33 of controlling global temperatures.…”