Elicitation of US and Chinese expert judgments show consistent views on solar geoengineering

The study examines how experts in the US and China view solar geoengineering (SG)—the deliberate alteration of Earth’s radiative forcing to reduce climate hazards—amid political contention, governance uncertainty, and growing attention in climate policy. Given the limitations and instability of public opinion on emerging technologies, expert judgments are influential in shaping media narratives and informing policy. Prior research has emphasized public views and document analyses with very few direct, structured elicitations of expert opinion. Because SG’s impacts and decisions about deployment require international collaboration, comparing expert views across major actors is crucial. The research focuses on US and Chinese experts due to the countries’ central roles in global emissions and climate policy and to test whether differing political systems, cultures, and histories produce divergent expert assessments. The study aims to assess (1) the views US and Chinese climate experts hold on SG-related risks, research, governance, and deployment, and (2) the extent of differences between these views.

The paper notes at least 45 studies of public opinion on SG but only six that directly consider experts, with most analyzing documents rather than eliciting judgments; only two prior studies directly gathered expert opinions and none used structured elicitation. Prior literature often posited differences between China and Western democracies due to philosophical traditions (e.g., Confucianism), histories of large engineering projects, and governance norms, suggesting potential divergence in SG policy preferences. There is also a growing body of work showing cautious openness to SG among laypeople and experts in developing countries. This study addresses the gap by applying structured elicitation to compare US and Chinese experts directly.

The study employed semi-structured, face-to-face interviews using a structured expert elicitation protocol with 13 US and 13 Chinese climate experts. Experts were recruited primarily via random selection from IPCC AR5 authors; due to the smaller Chinese pool, snowball sampling supplemented recruitment. The overall response rate was 19%. Interviews covered three topics: (1) climate risks and emissions/radiative forcing (RF) trajectories; (2) risks, benefits, and governance of SG deployment; and (3) the scale, content, and governance of SG research. Interviews were conducted in Chinese (China: June–August 2018) and English (US: October 2018–May 2019) with translated guides; only identical questions across versions were analyzed. Quantitative analyses used Student’s t-tests, Mann–Whitney tests for numerical/ranked questions, and z-tests for selection items; significance threshold p<0.05 (two-tailed). Rankings with ties were rescaled to preserve rank-sum; selection answers were one-hot encoded. Missing values were omitted (or imputed as sample mean for hierarchical agglomerative clustering, HAC). Correlations (Simpson’s) were computed for quantitative responses. HAC clustering was conducted both across experts and across questions after standardization (mean 0, SD 1), using group-averaged Euclidean distances. No multiple-comparisons corrections were applied to reduce Type II error in highlighting potential divergences. In addition, a structured online survey was administered to SG researchers recruited around the 2018 AGU Fall Meeting. For comparison, a subsample of 19 SG experts (≥10 peer-reviewed publications on SG by Web of Science search, May 20, 2020) was analyzed on overlapping questions (Q3, Q6, Q10).

• Broad cross-national agreement: Across most quantitative judgments, US and Chinese experts showed strong agreement on climate risks, expected RF trajectories, research funding levels, and caution toward deployment. HAC analysis found no clustering by nationality.
• Climate hazards (Q1): Both groups ranked extreme heat and related changes highest in importance; sea level/sea ice and ocean acidification ranked lowest nationally for this century. A significant difference: Chinese experts ranked extreme precipitation/inland flooding highest, citing infrastructure and human/economic impacts; US experts ranked it lowest and emphasized sea-level rise/coastal flooding due to coastal population/property exposure.
• China emissions trajectories (Q2): Chinese experts estimated lower 2075 CO2 emissions, lower peaks, and earlier peak years than US experts; differences were small and statistically significant only for upper-bound estimates. Chinese cited trust in government NDC (peak by 2030); US highlighted economic/population growth uncertainties.
• Expected 2075 RF (Q3): Mean ≈4.3 W/m² (near RCP4.5). US experts exhibited a broader uncertainty range; Chinese 10th–90th percentile fell within the US range.
• Desired RF and SG use by 2075 (Q10): US experts desired significantly lower RF than Chinese by about 1.3 W/m², implying more aggressive climate goals. Despite this, few endorsed SG deployment: only 2 US and 2 Chinese experts would use SG to offset RF by 2075; two additional US experts might use SG before 2075 but return SG RF to zero by 2075.
• Perceived benefits/risks (Q14–Q15): Key uncertainty in efficacy: impacts on regional climate/monsoons cited by over half. Most important physical hazard differed: Chinese often cited stratospheric ozone impacts; US cited other environmental impacts of implementation. Most important socio-economic risk differed: US emphasized governance difficulties; Chinese emphasized conflicts from varied regional outcomes.
• Governance preferences (Q11): Both favored international governance over consortia or no international governance. Venue preference differed: all Chinese preferred extending UNFCCC; most US preferred a new formal UN treaty mechanism, citing UNFCCC’s slow, consensus-driven processes.
• Likelihood of US/China being first movers (Q12): Average ≈50% (coin flip) with large dispersion (SD ≈34%). Arguments for: inclusion in international efforts, capability, emergencies; against: outcome uncertainty, risk aversion, need for global agreement.
• Culture and past projects (Q17–Q20): Experts generally felt culture would not significantly affect deployment probability, though definitions of culture varied by country and overlapped little. Chinese experts more frequently referenced domestic engineering projects and believed domestic project experience could affect SG deployment; US experts referenced international projects and fewer saw domestic projects as influential.
• Research program design and funding (Q4–Q7): Unanimous support for increased SG research funding. Experts allocated on average 5% (median 4%; 10th–90th ≈1–10%) of climate research budgets to a loosely coordinated SG program by 2030, versus <0.3% actual funding (circa 2018). Funding distribution: on average 66% to natural science activities (e.g., modeling impacts 21%; ethics 7%); perceived importance similarly weighted (≈62% to natural sciences). Many supported small-scale outdoor experiments under independent governance; few supported short-term large-scale experiments; limited support for deployment hardware R&D.
• National roles and information sources (Q8–Q9): Most US experts favored a leading, significant research role; most Chinese favored some original research contributing to the field. IPCC was the most preferred information source overall; US experts preferred domestic academics over IPCC and trusted the UN least.
• Regulation of research (Q7): Just over half (9 US, 6 China) felt no additional regulation was needed beyond standard health and safety; others suggested constraints such as containment where possible.
• Comparison with SG experts (survey): SG experts similarly supported higher research funding (mean/median ≈2 percentage points higher than interviewees; not statistically significant). SG experts were more open to deployment: 6/19 indicated non-zero desired SG RF in 2075 versus 4/26 among climate experts.

Findings indicate substantial convergence between US and Chinese climate experts on SG-related judgments, contradicting prior expectations of strong cross-national divergence rooted in cultural or political differences. Agreement spans expected climate trajectories, research priorities, and skepticism toward near-term deployment, suggesting a basis for collaborative research initiatives and potential policy coordination. Differences that could shape future negotiations include the aggressiveness of desired climate goals (US lower desired RF) and preferred governance venues (China: extend UNFCCC; US: new UN treaty mechanism). Experts’ caution toward deployment and emphasis on regional climate uncertainties highlight the need for robust governance and continued research. The comparison with SG specialists suggests that those deeply engaged in SG research are somewhat more supportive of deployment than general climate experts, an asymmetry policymakers should consider when interpreting expert advice.

The study provides the first structured, cross-national elicitation comparing US and Chinese climate experts on SG. It finds broad consensus supporting a substantial increase in SG research funding (mean ≈5% of climate science budgets) and strong caution regarding deployment, with only a few experts endorsing SG use by 2075. Despite differing preferences on governance venues and climate goal stringency, the overall alignment suggests opportunities for US–China collaboration on SG research and dialogue. These results challenge assumptions of pronounced US–China divergence on SG and underscore the value of structured expert elicitation to inform policy debates.

• Sample size and representativeness: Small N (13 US, 13 China) and a 19% response rate. Chinese interviewees over-represent university affiliations and under-represent government-affiliated researchers relative to overall IPCC authorship, potentially biasing results.
• Recruitment and design differences: China sample included snowball sampling and non-IPCC experts; US sample was randomly drawn from IPCC authors only. Minor differences existed between national interview guides (only identical questions analyzed); US interviews included an additional global emissions question.
• Methodological choices: No multiple-comparisons corrections were applied to hypothesis tests (to reduce Type II error), increasing potential Type I error risk. Missing data handling (imputation to sample mean for HAC) may influence clustering outcomes.
• Format differences in comparison group: The SG expert data came from an online survey, whereas climate experts were interviewed in person; mode effects may influence comparability.
• Generalizability and data access: Confidentiality limits public access to transcripts; cultural interpretations varied among experts; results may not generalize to broader expert populations or other countries.