The cost-effective mitigation of climate change through nature-based carbon dioxide removal strategies has gained substantial policy attention. Inland and coastal wetlands (specifically boreal, temperate and tropical peatlands; tundra; floodplains; freshwater marshes; saltmarshes; and mangroves) are among the most efficient natural long-term carbon sinks. Yet, they also release methane (CH₄) that can offset the carbon they sequester. Here, we conducted a meta-analysis on wetland carbon dynamics to (i) determine their impact on climate using different metrics and time horizons, (ii) investigate the cost-effectiveness of wetland restoration for climate change mitigation, and (iii) discuss their suitability for inclusion in climate policy as negative emission technologies. Depending on metrics, a wetland can simultaneously be a net carbon sink (i.e. boreal and temperate peatlands net ecosystem carbon budget = −28.1 ± 19.13 gC m⁻² y⁻¹) but have a net warming effect on climate at the 100 years time-scale (i.e. boreal and temperate peatland sustained global warming potential = 298.2 ± 100.6 gCO₂ eq⁻¹ m⁻² y⁻¹). This situation creates ambivalence regarding the effect of wetlands on global temperature. Moreover, our review reveals high heterogeneity among the (limited number of) studies that document wetland carbon budgets. We demonstrate that most coastal and inland wetlands have a net cooling effect as of today. This is explained by the limited CH₄ emissions that undisturbed coastal wetlands produce, and the long-term carbon sequestration performed by older inland wetlands as opposed to the short lifetime of CH₄ in the atmosphere. Analysis of wetland restoration costs relative to the amount of carbon they can sequester revealed that restoration is more cost-effective in coastal wetlands such as mangroves (US$1800 ton C⁻¹) compared with inland wetlands (US$4200–49 200 ton C⁻¹). We advise that for inland wetlands, priority should be given to conservation rather than restoration; while for coastal wetlands, both conservation and restoration may be effective techniques for climate change mitigation.

通过基于自然的二氧化碳去除策略以具有成本效益的方式缓解气候变化已经获得了大量的政策关注。内陆和沿海湿地（特别是北方、温带和热带泥炭地；苔原；漫滩；淡水沼泽；盐沼；和红树林）是最有效的自然长期碳汇。然而，它们也会释放甲烷（CH ₄) 可以抵消它们封存的碳。在这里，我们对湿地碳动态进行了荟萃分析，以 (i) 使用不同的指标和时间范围确定它们对气候的影响，(ii) 调查湿地恢复缓解气候变化的成本效益，以及 (iii) 讨论它们的适合作为负排放技术纳入气候政策。根据指标，湿地可以同时是净碳汇（即北方和温带泥炭地净生态系统碳预算 = -28.1 ± 19.13 gC m ^-2 y ^-1）但在 100 年时间对气候具有净变暖效应 -规模（即北方和温带泥炭地持续全球变暖潜势 = 298.2 ± 100.6 gCO ₂ eq ^-1 m ^-2y ^-1 )。这种情况在湿地对全球温度的影响方面造成了矛盾。此外，我们的审查揭示了记录湿地碳预算的（数量有限的）研究之间的高度异质性。我们证明，截至今天，大多数沿海和内陆湿地都具有净降温效果。这是由于未受干扰的沿海湿地产生的CH ₄排放有限，以及较老的内陆湿地进行的长期碳固存，而不是 CH ₄在大气中的短寿命。湿地恢复成本相对于它们可以固存的碳量的分析表明，在沿海湿地如红树林（1800 吨 C ^-1) 与内陆湿地 (US$4200–49 200 吨 C ^-1 ) 相比。我们建议内陆湿地应优先保护而不是恢复；而对于沿海湿地，保护和恢复可能是减缓气候变化的有效技术。