Environmental Defense Fund, New York City, NY, 10010, USA.
Sci Rep. 2021 Nov 12;11(1):22173. doi: 10.1038/s41598-021-01639-y.
Net zero greenhouse gas targets have become a central element for climate action. However, most company and government pledges focus on the year that net zero is reached, with limited awareness of how critical the emissions pathway is in determining the climate outcome in both the near- and long-term. Here we show that different pathways of carbon dioxide and methane-the most prominent long-lived and short-lived greenhouse gases, respectively-can lead to nearly 0.4 °C of warming difference in midcentury and potential overshoot of the 2 °C target, even if they technically reach global net zero greenhouse gas emissions in 2050. While all paths achieve the Paris Agreement temperature goals in the long-term, there is still a 0.2 °C difference by end-of-century. We find that early action to reduce both emissions of carbon dioxide and methane simultaneously leads to the best climate outcomes over all timescales. We therefore recommend that companies and countries supplement net zero targets with a two-basket set of interim milestones to ensure that early action is taken for both carbon dioxide and methane. A one-basket approach, such as the standard format for Nationally Determined Contributions, is not sufficient because it can lead to a delay in methane mitigation.
净零温室气体目标已成为气候行动的核心要素。然而，大多数公司和政府的承诺都集中在实现净零的年份，而对确定近期和长期气候结果的排放途径的重要性认识有限。在这里，我们表明，二氧化碳和甲烷的不同途径——分别是最主要的长寿命和短寿命温室气体——可能导致本世纪中叶升温差异近 0.4°C，并有可能超过 2°C 的目标，即使它们在技术上能在 2050 年实现全球温室气体净零排放。虽然所有途径在长期内都能实现《巴黎协定》的温度目标，但到本世纪末仍有 0.2°C 的差异。我们发现，尽早采取行动同时减少二氧化碳和甲烷的排放，会在所有时间尺度上带来最佳的气候结果。因此，我们建议公司和国家在净零目标之外，设置两篮子的中期里程碑，以确保尽早采取行动来减少二氧化碳和甲烷。一篮子的方法，如国家自主贡献的标准格式，是不够的，因为它可能导致甲烷减排的延迟。
