Atmospheric methane (CH₄) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era¹. Fossil fuel extraction and use are among the largest anthropogenic sources of CH₄ emissions, but the precise magnitude of these contributions is a subject of debate^2,3. Carbon-14 in CH₄ (¹⁴CH₄) can be used to distinguish between fossil (¹⁴C-free) CH₄ emissions and contemporaneous biogenic sources; however, poorly constrained direct ¹⁴CH₄ emissions from nuclear reactors have complicated this approach since the middle of the 20th century^4,5. Moreover, the partitioning of total fossil CH₄ emissions (presently 172 to 195 teragrams CH₄ per year)^2,3 between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH₄ per year^6,7. Geological emissions were less than 15.4 teragrams CH₄ per year at the end of the Pleistocene, about 11,600 years ago⁸, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core ¹⁴CH₄ measurements to show that natural geological CH₄ emissions to the atmosphere were about 1.6 teragrams CH₄ per year, with a maximum of 5.4 teragrams CH₄ per year (95 per cent confidence limit)—an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH₄ emissions are underestimated by about 38 to 58 teragrams CH₄ per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH₄ budget, and will help to inform strategies for targeted emission reductions^9,10.

大气中的甲烷 (CH ₄ ) 是一种强效温室气体，其摩尔分数自前工业时代以来增加了一倍多¹。化石燃料的开采和使用是 CH ₄排放的最大人为来源之一，但这些贡献的确切幅度是一个有争议的主题^2,3。CH ₄ ( ¹⁴ CH ₄ ) 中的碳 14可用于区分化石（不含¹⁴ C）CH ₄排放和同期生物源；然而，约束较差的直接¹⁴ CH ₄自 20 世纪中叶以来，核反应堆的排放使这种方法变得复杂^4,5。此外，人为和自然地质来源（如渗漏和泥火山）之间的化石 CH ₄排放总量（目前每年172 至 195 太克 CH _{4 ）} ^{2,3的划分正在辩论中；}排放清单表明，后者每年约占 40 至 60 太克 CH ₄ ^6,7。大约 11,600 年前的更新世末期，地质排放量每年不到 15.4 太克 CH ₄ ⁸，但由于大面积的陆地冰盖覆盖、较低的海平面和广泛的永久冻土，这一时期与当今的排放量相比是一个不完美的模拟。在这里，我们使用前工业时代冰芯¹⁴ CH ₄测量结果表明，向大气排放的自然地质 CH ₄约为每年 1.6 太克 CH ₄，每年最多为 5.4 太克 CH ₄（95% 的置信限）—比目前使用的估计值低一个数量级。该结果表明人为化石 CH ₄排放被低估了约 38 至 58 太克 CH ₄每年，或大约是最近估计的 25% 至 40%。我们的记录突出了人类对大气和气候的影响，为全球 CH ₄预算清单提供了一个明确的目标，并将有助于为有针对性的减排战略提供信息^9,10。