Solar geoengineering refers to deliberately reducing net radiative forcing by reflecting some sunlight back to space, in order to reduce anthropogenic climate changes; a possible such approach would be adding aerosols to the stratosphere. If future mitigation proves insufficient to limit the rise in global mean temperature to less than 1.5°C above preindustrial, it is plausible that some additional and limited deployment of solar geoengineering could reduce climate damages. That is, these approaches could eventually be considered as part of an overall strategy to manage the risks of climate change, combining emissions reduction, net-negative emissions technologies and solar geoengineering to meet climate goals. We first provide a physical science review of current research, research trends and some of the key gaps in knowledge that would need to be addressed to support informed decisions. Next, since few climate model simulations have considered these limited-deployment scenarios, we synthesize prior results to assess the projected response if solar geoengineering were used to limit global mean temperature to 1.5°C above preindustrial in an overshoot scenario that would otherwise peak near 3°C. While there are some important differences, the resulting climate is closer in many respects to a climate where the 1.5°C target is achieved through mitigation alone than either is to the 3◦C climate with no geoengineering. This holds for both regional temperature and precipitation changes; indeed, there are no regions where a majority of models project that this moderate level of geoengineering would produce a statistically significant shift in precipitation further away from preindustrial levels. This article is part of the theme issue ‘The Paris Agreement: understanding the physical and social challenges for a warming world of 1.5°C above pre-industrial levels’.
We study the possibility of designing solar radiation management schemes to achieve a desired meridional radiative forcing (RF) profile using a two-dimensional chemistry-transport-aerosol model. Varying SO2 or H2SO4 injection latitude, altitude, and season, we compute RF response functions for a broad range of possible injection schemes, finding that linear combinations of these injection cases can roughly achieve RF profiles that have been proposed to accomplish various climate objectives. Globally averaged RF normalized by the sulfur injection rate (the radiative efficacy) is largest for injections at high altitudes, near the equator, and using emission of H2SO4 vapor into an aircraft wake to produce accumulation-mode particles. There is a trade-off between radiative efficacy and control as temporal and spatial control is best achieved with injections at lower altitudes and higher latitudes. These results may inform studies using more realistic models that couple aerosol microphysics, chemistry, and stratospheric dynamics.
Increasing interest in climate engineering in recent years has led to calls by the international research community for international research collaboration as well as global public engagement. But making such collaboration a reality is challenging. Here, we report the summary of a 2016 workshop on the significance and challenges of international collaboration on climate engineering research with a focus on the Asia-Pacific region. Because of the region’s interest in benefits and risks of climate engineering, there is a potential synergy between impact research on anthropogenic global warming and that on solar radiation management. Local researchers in the region can help make progress toward better understanding of impacts of solar radiation management. These activities can be guided by an ad hoc Asia-Pacific working group on climate engineering, a voluntary expert network. The working group can foster regional conversations in a sustained manner while contributing to capacity building. An important theme in the regional conversation is to develop effective practices of dialogues in light of local backgrounds such as cultural traditions and past experiences of large-scale technology development. Our recommendation merely portrays one of several possible ways forward, and it is our hope to stimulate the debate in the region.
Solar geoengineering is no substitute for cutting emissions, but could nevertheless help reduce the atmospheric carbon burden. In the extreme, if solar geoengineering were used to hold radiative forcing constant under RCP8.5, the carbon burden may be reduced by ~100 GTC, equivalent to 12–26% of twenty-first-century emissions at a cost of under US$0.5 per tCO2.
Discourse on social media of solar geoengineering has been rapidly increasing over the past decade, in line with increased attention by the scientific community and low but increasing awareness among the general public. The topic has also found increased attention online. But unlike scientific discourse, a majority of online discussion focuses on the so-called chemtrails conspiracy theory, the widely debunked idea that airplanes are spraying a toxic mix of chemicals through contrails, with supposed goals ranging from weather to mind control. This paper presents the results of a nationally representative 1000-subject poll part of the 36,000-subject 2016 Cooperative Congressional Election Study (CCES), and an analysis of the universe of social media mentions of geoengineering. The former shows ~ 10% of Americans declaring the chemtrails conspiracy as “completely” and a further ~ 20–30% as “somewhat” true, with no apparent difference by party affiliation or strength of partisanship. Conspiratorial views have accounted for ~ 60% of geoengineering discourse on social media over the past decade. Of that, Twitter has accounted for >90%, compared to ~ 75% of total geoengineering mentions. Further affinity analysis reveals a broad online community of conspiracy. Anonymity of social media appears to help its spread, so does the general ease of spreading unverified or outright false information. Online behavior has important real-world reverberations, with implications for climate science communication and policy.