Arctic sea ice has steadily diminished as atmospheric greenhouse gas concentrations have increased. Using observed data from 1979 to 2019, we estimate a close contemporaneous linear relationship between Arctic sea ice area and cumulative carbon dioxide emissions. For comparison, we provide analogous regression estimates using simulated data from global climate models (drawn from the CMIP5 and CMIP6 model comparison exercises). The carbon sensitivity of Arctic sea ice area is considerably stronger in the observed data than in the climate models. Thus, for a given future emissions path, an ice-free Arctic is likely to occur much earlier than the climate models project. Furthermore, little progress has been made in recent global climate modeling (from CMIP5 to CMIP6) to more accurately match the observed carbon-climate response of Arctic sea ice.

翻译：随着大气温室气体浓度增加，北极海冰面积持续缩小。基于1979年至2019年的观测数据，我们估算出北极海冰面积与累计二氧化碳排放量之间存在紧密的同期线性关系。为进行比较，我们利用全球气候模型（来自CMIP5和CMIP6模式比较计划）的模拟数据提供了类似的回归估计结果。观测数据中北极海冰面积对碳排放的敏感性显著强于气候模型所呈现的结果。因此，对于给定的未来排放路径，北极无冰期的出现时间很可能远早于气候模型的预测。此外，近年来的全球气候模拟工作（从CMIP5到CMIP6）在更精确匹配观测到的北极海冰碳-气候响应方面进展甚微。