ABSTRACT

Solar geoengineering (SG) might be able to reduce climate risks if used to supplement emissions cuts and carbon removal. Yet, the wisdom of proceeding with research to reduce its uncertainties is disputed. Here, we use an integrated assessment model to estimate that the value of information that reduces uncertainty about SG efficacy. We find the value of reducing uncertainty by one-third by 2030 is around $4.5 trillion, most of which comes from reduced climate damages rather than reduced mitigation costs. Reducing uncertainty about SG efficacy is similar in value to reducing uncertainty about climate sensitivity. We analyse the cost of over-confidence about SG that causes too little emissions cuts and too much SG. Consistent with concerns about SG’s moral hazard problem, we find an over-confident bias is a serious and costly concern; but, we also find under-confidence that prematurely rules out SG can be roughly as costly. Biased judgments are costly in both directions. A coin has two sides. Our analysis quantitatively demonstrates the risk-risk trade-off around SG and reinforces the value of research that can reduce uncertainty.

Key policy insights

• The value of reducing uncertainty about solar geoengineering is comparable to the value of reducing uncertainty about other key climate factors, such as equilibrium climate sensitivity.

• The benefits of research that reduces uncertainty about solar geoengineering may be more than a thousand times larger than the cost of a large-scale research programme.

• Under-confidence in solar geoengineering’s effectiveness can be as costly as over-confidence.

• The majority of the benefits of reduced uncertainty come from reducing climate damages rather than from slowing emissions reductions.

摘要

如果用于补充减排和碳清除，太阳能地球工程 (SG) 可能能够降低气候风险。然而，继续进行研究以减少其不确定性是否明智是有争议的。在这里，我们使用综合评估模型来估计减少 SG 功效不确定性的信息的价值。我们发现，到 2030 年将不确定性降低三分之一的价值约为 4.5 万亿美元，其中大部分来自减少气候损害，而不是降低缓解成本。减少 SG 功效的不确定性与减少气候敏感性的不确定性在价值上是相似的。我们分析了导致减排量过少和 SG 过多的对 SG 过度自信的成本。与对 SG 道德风险问题的担忧一致，我们发现过度自信的偏见是一个严重且代价高昂的问题；但，我们还发现过早排除 SG 的信心不足可能会造成大致相同的代价。有偏见的判断在两个方面都会付出高昂的代价。一枚硬币有两个面。我们的分析定量地证明了围绕 SG 的风险-风险权衡，并强化了可以减少不确定性的研究的价值。

关键政策见解

• 减少太阳能地球工程不确定性的价值与减少其他关键气候因素（例如平衡气候敏感性）不确定性的价值相当。

• 减少太阳能地球工程不确定性的研究的好处可能比大规模研究计划的成本大一千倍以上。

• 对太阳能地球工程有效性的信心不足可能与过度自信一样代价高昂。

• 减少不确定性的大部分好处来自于减少气候损害，而不是来自减缓减排。