This briefing addresses grave scientific concerns in relation to proposed geoengineering techniques such as solar radiation management (SRM). “Geoengineering” as used here does not refer to negative emissions technologies that remove CO2 from the atmosphere (carbon dioxide removal or CDR) as part of the energy system or through ecosystem restoration and afforestation or reforestation. Here we specifically address the risks posed by SRM.

Solar radiation management is not a solution to the climate problem

Solar radiation management does not address the drivers of human-induced climate change, nor does it address the full range of climate and other impacts of
anthropogenic greenhouse gas and air pollutant emissions. Solar radiation management aims at limiting temperature increase by deflecting sunlight, mostly
through injection of particles into the atmosphere. At best, SRM would mask warming temporarily, but more fundamentally is itself a potentially dangerous interference with the climate system.

Solar radiation management would alter the global hydrological cycle as well as fundamentally affect global circulation patterns such as monsoons. Substantial
monsoon disruptions induced by SRM cannot be ruled out. SRM may not halt ocean warming around Antarctica and would fail to counteract the increasing contribution of Antarctic melt to sea level rise.

Solar radiation management does not halt, reverse or address in any other way the profound and dangerous problem of ocean acidification which threatens coral reefs and marine life as it does not reduce CO2 emissions and hence influence atmospheric CO2 concentration. SRM does not counter other effects of increased CO2 concentration adversely affecting the terrestrial and marine biosphere. SRM is unlikely to attenuate the effects of global warming on global agricultural
production. Its potentially positive effect due to cooling is projected to be counterbalanced by negative effects on crop production of reducing solar radiation at
the earth’s surface.

There is very high scientific uncertainty on the potential impacts of solar radiation management, and these cannot be resolved by field experiments. Most studies of solar radiation management are based on highly idealised scenarios and assumptions that differ substantially from discussed, real-world applications of solar radiation management. Results of idealised experiments should not be conflated with discussions around solar radiation management ‘solutions’ based on very different techniques.

Solar radiation management would undermine renewable energy potentials. As it reduces the amount of solar radiation reaching the earth’s surface, solar radiation management would greatly diminish the potential one of the biggest alternatives to fossil fuel electricity generation: solar energy.

Solar radiation management poses fundamental risks to global governance and cooperation

Solar radiation management could be undertaken unilaterally, creating massive climate risks for many others. SRM would strongly alter the climate system producing ‘winners’ and ‘losers’ in different regions and with different levels of deployment. It would therefore most likely become a source of massive conflict between nations. If not banned completely, it would put the power of triggering a climate shock into the hands of single actors.

Solar radiation management is in contradiction with the ultimate objective of the UNFCCC which is to prevent dangerous interference with the climate system.
Geoengineering techniques like solar radiation management come with grave risks and themselves constitute a new, dangerous anthropogenic interference with the climate system, on top of emitting carbon dioxide and other greenhouse gases into the atmosphere.

Solar radiation management poses pivotal problems of intergenerational justice. Techniques like solar radiation management have to be continuously sustained. If disrupted, very rapid and large-scale planetary warming will occur on a timescale of months. The impacts of such a “termination shock” would be much worse than the effects of climate change it aims to avoid. As SRM does not reduce CO2, future generations would effectively be handed highly acidic oceans which cannot be easily reversed, if at all, with large scale damages to coral reefs and other marine ecosystems.