The magnitude of global cooling during the Last Glacial Maximum (LGM, the coldest multimillennial interval of the last glacial period) is an important constraint for evaluating estimates of Earth’s climate sensitivity^1,2. Reliable LGM temperatures come from high-latitude ice cores^3,4, but substantial disagreement exists between proxy records in the low latitudes^1,5,6,7,8, where quantitative low-elevation records on land are scarce. Filling this data gap, noble gases in ancient groundwater record past land surface temperatures through a direct physical relationship that is rooted in their temperature-dependent solubility in water^9,10. Dissolved noble gases are suitable tracers of LGM temperature because of their complete insensitivity to biological and chemical processes and the ubiquity of LGM-aged groundwater around the globe^11,12. However, although several individual noble gas studies have found substantial tropical LGM cooling^13,14,15,16, they have used different methodologies and provide limited spatial coverage. Here we use noble gases in groundwater to show that the low-altitude, low-to-mid-latitude land surface (45 degrees south to 35 degrees north) cooled by 5.8 ± 0.6 degrees Celsius (mean ± 95% confidence interval) during the LGM. Our analysis includes four decades of groundwater noble gas data from six continents, along with new records from the tropics, all of which were interpreted using the same physical framework. Our land-based result broadly supports a recent reconstruction based on marine proxy data assimilation¹ that suggested greater climate sensitivity than previous estimates^5,6,7.

末次盛冰期（LGM，末次冰期最冷的千年间隔）期间全球降温的幅度是评估地球气候敏感性^1,2估计值的重要限制因素。可靠的 LGM 温度来自高纬度冰芯^{3,4 ，但在低纬度地区1,5,6,7,8}的代理记录之间存在重大分歧，在这些地区，陆地上的定量低海拔记录很少。填补这一数据空白，古代地下水中的惰性气体通过直接的物理关系记录过去的地表温度，这种关系植根于它们在水中的温度依赖性溶解度^9,10. 溶解的惰性气体是 LGM 温度的合适示踪剂，因为它们对生物和化学过程完全不敏感，而且全球各地普遍存在 LGM 老化的地下水^11,12。然而，尽管几项单独的惰性气体研究发现热带 LGM 显着冷却^13,14,15,16，他们使用了不同的方法并提供了有限的空间覆盖范围。在这里，我们使用地下水中的惰性气体来表明，低海拔、中低纬度地表（南纬 45 度至北纬 35 度）在LG电子。我们的分析包括来自六大洲的四个十年的地下水惰性气体数据，以及来自热带的新记录，所有这些都是使用相同的物理框架进行解释的。我们基于陆地的结果广泛支持最近基于海洋代理数据同化¹的重建，该重建表明气候敏感性高于先前的估计^5,6,7。