The Influence of Stratospheric Sulphate Aerosol Deployment on the Surface Air Temperature and the Risk of an Abrupt Global Warming

Abstract

Abstract:We used the ‗Radiative-Convective Model of the Earth-atmosphere system' (OGIM) to investigate the cooling effects induced by sulphur injections into the stratosphere. The ensemble of numerical calculations was based on the A1B scenario from the IPCC Special Report on Emissions Scenarios (SRES). Several geoengineered scenarios were analysed, including the abrupt interruption of these injections in different scenarios and at different dates. We focused on the surface air temperature (SAT) anomalies induced by stratospheric sulphate aerosol generated in order to compensate future warming. Results show that continuous deployment of sulphur into the stratosphere could induce a lasting decrease in SAT. Retaining a constant aerosol loading equivalent to 6 TgS would delay the expected global warming by 53 years. Keeping the SAT constant in a context of increasing greenhouse gases (GHGs) means that the aerosol loading needs to be increased by 1.9% annually. This would offset the effect of increasing GHG under the A1B scenario. A major focus of this study was on the heating rates of SAT that would arise in different scenarios in case of an abrupt cessation of sulphur injections into the stratosphere. Our model results show that heating rates after geoengineering interruption would be 15-28 times higher than in a case without geoengineering, with likely important consequences for life on Earth. Larger initial sulphate loadings induced OPEN ACCESSAtmosphere 2010, 1 63 more intense warming rates when the geoengineering was stopped at the same time. This implies that, if sulphate loading was increased to maintain constant SAT in the light of increasing GHG concentrations, the later the geoengineering interruption was to occur, the higher the heating rates would be. Consequently, geoengineering techniques like this should only be regarded as last-resort measures and require intense further research should they ever become necessary.

Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario

“…10 ). For temperature, this termination effect is well known and has been consistently reproduced in SRM studies 28 29 30 31 32 . However, there is much less certainty concerning the response of the carbon cycle to SRM discontinuation 30 .…”

Role of volcanic forcing on future global carbon cycle

“…For example, the potential stratospheric ozone destruction, potential acid rain, effects on cirrus clouds, impacts of the released volcanic dust on terrestrial and marine ecosystem (Sarmiento, 1993;Duggen et al, 2010), and changes in regional atmospheric and ocean circulation that may need decades or centuries to recover (Jones et al, 2011). All of these factors remain poorly understood and the recent geoengineering studies (Matthews and Caldeira, 2007;Jones et al, 2010;Llanillo et al, 2010) include the warning that, should geoengineering fail or be stopped abruptly, it could lead to very rapid climate change, with warming rates up to 20 times greater than present-day rates. Even if such methods can be deployed successfully, our study suggests that a high concentration of atmospheric CO 2 would remain in the atmosphere for a long time.…”

The Risk of Termination Shock From Solar Geoengineering

“…SRM only masks the warming effects of GHGs and is not designed to reduce their concentrations in the atmosphere. Therefore, if SRM were ever used to mask a high level of warming and its deployment were terminated suddenly, temperature would rebound toward the levels they would have reached without the geoengineering (Brovkin et al, ; Irvine et al, ; Jones et al, ; Llanillo et al, ; Matthews & Caldeira, ; McCusker et al, , ). This effect is referred to as “termination shock” or “termination effect.” Termination shock could be very damaging for natural and human systems as the rate of warming would probably be much higher than that otherwise expected under anthropogenic climate change (Irvine et al, ; Llanillo et al, ; Matthews & Caldeira, ; McCusker et al, ), meaning that both ecosystems and human societies would have less time to adapt to the rapidly changing new conditions (McCormack et al, ; Trisos et al, ).…”

“…In numerous academic papers (see, e.g., Brovkin et al, ; Clark et al, ; Pidgeon et al, ; Vaughan & Lenton, ) and high‐profile commentary pieces (Appell, ; Dean, ; Klein, ; Pierrehumbert, ; Plumer, ), it is claimed that once deployed, SRM would need to be maintained for centuries or even millennia to avoid the risk of termination shock. It has also been argued that due to the risk of termination shock, SRM should only be considered an option of last resort for emergency use (Llanillo et al, ) or that the cooling from any deployment of SRM should be limited to a level that would not cause a dangerous temperature rebound in the event of termination (Kosugi, ). Aggressive mitigation would need to be a prerequisite of SRM deployment in the opinion of McCusker et al (), while Kruger () takes this idea one stage further, arguing not only that SRM should not be deployed without an “exit plan” in the form of very large‐scale carbon dioxide removal technologies but also that those costs should be seen as an integral component of the costs of SRM.…”