A review of climate geoengineering proposals

Abstract

Climate geoengineering proposals seek to rectify the current radiative imbalance via either (1) reducing incoming solar radiation (solar radiation management) or (2) removing CO2 from the atmosphere and transferring it to long-lived reservoirs (carbon dioxide removal). For each option, we discuss its effectiveness and potential side effects, also considering lifetime of effect, development and deployment timescale, reversibility, and failure risks. We present a detailed review that builds on earlier work by including the most recent literature, and is more extensive than previous comparative frameworks. Solar radiation management propsals are most effective but short-lived, whilst carbon dioxide removal measures gain effectiveness the longer they are pursued. Solar radiation management could restore the global radiative balance, but must be maintained to avoid abrupt warming, meanwhile ocean acidification and residual regional climate changes would still occur. Carbon dioxide removal involves less risk, and offers a way to return to a pre-industrial CO2 level and climate on a millennial timescale, but is potentially limited by the CO2 storage capacity of geological reservoirs. Geoengineering could complement mitigation, but it is not an alternative to it. We expand on the possible combinations of mitigation, carbon dioxide removal and solar radiation management that might be used to avoid dangerous climate change

Interactions between reducing CO 2 emissions, CO 2 removal and solar radiation management

“…where A is the (fixed) surface albedo (A = 0.225), S is the incoming solar flux at the top of the atmosphere (S = 1368 W m −2 ) and t is the (equivalent grey) vertical opacity of the greenhouse atmosphere, which depends on the concentrations of CO 2 , H 2 O (g) and CH 4 . The opacity of each gas is assumed to be independent of the others [8]:…”

“…Our method of back-calculating the amount of SRM required to maintain pre-industrial temperatures (figures 3c and 9c) hides a considerable challenge for any choice of SRM method: that of continually modifying its magnitude. Not all suggested SRM methods could achieve this [4]. The challenge is made more difficult if the real Earth system has a relatively high heat capacity, and hence temperature responds more slowly to radiative forcing perturbations.…”

Impacts of light shading and nutrient enrichment geo-engineering approaches on the productivity of a stratified, oligotrophic ocean ecosystem

“…We do not undertake an assessment of geo-engineering approaches per se, as this has been published elsewhere [4,[27][28][29]. Neither do we consider the global carbon sequestration or cooling potential of these approaches nor feedbacks of geo-engineering approaches on ocean physics as these would require an alternative modelling framework (fully coupled, three-dimensional ocean-atmosphere-ecosystem model, e.g.…”

Ocean Iron Fertilization Experiments: Past–Present–Future with Introduction to Korean Iron Fertilization Experiment in the Southern Ocean (KIFES) Project

“…Various ideas/approaches have been proposed to relieve/resolve the problem of global warming (Matthews, 1996;Lenton and Vaughan, 2009;Vaughan and Lenton, 2011;IPCC, 2014;Leung et al, 2014;Ming et al, 2014), largely based on two categories: (1) reduction of atmospheric CO 2 -ocean fertilization to enhance biological CO 2 uptake and/or direct capture or storage of atmospheric CO 2 through chemically engineered processes, and (2) control of solar radiation -artificial aerosol 10 injection into the atmosphere to augment cloud formation and cloud brightening to elevate albedo (Fig. 2).…”