International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria.
Geography Department and IRITHESys Institute, Humboldt-Universität zu Berlin, Berlin, Germany.
Nature. 2024 Oct;634(8033):366-373. doi: 10.1038/s41586-024-08020-9. Epub 2024 Oct 9.
Global emission reduction efforts continue to be insufficient to meet the temperature goal of the Paris Agreement. This makes the systematic exploration of so-called overshoot pathways that temporarily exceed a targeted global warming limit before drawing temperatures back down to safer levels a priority for science and policy. Here we show that global and regional climate change and associated risks after an overshoot are different from a world that avoids it. We find that achieving declining global temperatures can limit long-term climate risks compared with a mere stabilization of global warming, including for sea-level rise and cryosphere changes. However, the possibility that global warming could be reversed many decades into the future might be of limited relevance for adaptation planning today. Temperature reversal could be undercut by strong Earth-system feedbacks resulting in high near-term and continuous long-term warming. To hedge and protect against high-risk outcomes, we identify the geophysical need for a preventive carbon dioxide removal capacity of several hundred gigatonnes. Yet, technical, economic and sustainability considerations may limit the realization of carbon dioxide removal deployment at such scales. Therefore, we cannot be confident that temperature decline after overshoot is achievable within the timescales expected today. Only rapid near-term emission reductions are effective in reducing climate risks.
全球减排力度持续不足，无法实现《巴黎协定》的温度目标。这使得系统探索所谓的“超越路径”成为当务之急，即在将温度降低到更安全水平之前，暂时超越目标全球变暖限制。在这里，我们表明，在出现超越之后，全球和区域气候变化及相关风险与避免超越的情况不同。我们发现，与仅仅稳定全球变暖相比，实现全球气温下降可以限制长期气候风险，包括海平面上升和冰冻圈变化。然而，未来几十年全球变暖可能逆转的可能性对于今天的适应规划来说可能意义不大。全球变暖的逆转可能会受到强烈的地球系统反馈的影响，导致近期和长期持续的高温。为了防范和应对高风险结果，我们确定了地球物理方面对数百千兆吨预防二氧化碳去除能力的需求。然而，技术、经济和可持续性方面的考虑因素可能会限制在这种规模上实现二氧化碳去除部署。因此，我们不能确定在今天预期的时间内是否能够实现超越后的温度下降。只有迅速减少近期排放才能有效降低气候风险。
