We investigate the influence of external forcings on the frequency of temperature extremes over land at the global and continental scales by comparing HadEX3 observations and simulations from the Coupled Model Intercomparison Programme Phase 6 (CMIP6) project. We consider four metrics including warm days and nights (TX90p and TN90p) and cold days and nights (TX10p and TN10p). The observational dataset during 1951–2018 shows continued increases in the warm days and nights and decreases in the cold days and nights in most land areas in the years after 2010. The area of the so-called "warming hole" in North America is much reduced in 1951–2018 compared with that in 1951–2010. The comparison between observation and simulations based on an optimal fingerprinting method shows that the anthropogenic forcing, dominated by greenhouse gases, plays the most important role in the changes of the frequency indices. Changes in CMIP6 multi-model mean response to all forcing need to be scaled down to best match the observations, indicating that the multi-model ensemble mean may have overestimated the observed changes. Analyses that involve signals from anthropogenic and natural external forcings confirm that the anthropogenic signal can be detected over global land as a whole and for most continents in all temperature indices. Analyses that include signals from greenhouse gas (GHG), anthropogenic aerosol (AA) and natural external (NAT) forcings show that the GHG signal is detected in all indices over the globe and most continents while the AA signal can be detected mainly in the warm extremes but not the cold extremes over the globe and most continents. The effect of NAT is negligible in most land areas. GHG's warming effect is offset partially by AA's cooling effect. The combined effects from both explain most of the observed changes over the globe and continents.

中文翻译：

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人类对极端温度频率的影响

我们通过比较耦合模型比对计划第 6 阶段 (CMIP6) 项目的 HadEX3 观测和模拟结果，研究了外部强迫对全球和大陆尺度陆地上极端温度频率的影响。我们考虑四个指标，包括温暖的昼夜（TX90p 和 TN90p）和寒冷的昼夜（TX10p 和 TN10p）。1951-2018年的观测数据显示，2010年后大部分陆地地区暖昼夜持续增加，冷昼夜减少。北美所谓的“暖洞”面积很大。 1951-2018 年与 1951-2010 年相比有所减少。基于最优指纹法的观测与模拟比较表明，以温室气体为主的人为强迫，在频率指标的变化中起着最重要的作用。CMIP6 多模式平均响应对所有强迫的变化需要按比例缩小以最好地匹配观测，这表明多模式集合平均值可能高估了观测到的变化。涉及来自人为和自然外强迫的信号的分析证实，可以在整个全球陆地和大多数大陆的所有温度指数中检测到人为信号。包括来自温室气体 (GHG)、人为气溶胶 (AA) 和自然外部 (NAT) 强迫信号的分析表明，在全球和大多数大陆的所有指数中都检测到了 GHG 信号，而 AA 信号主要可以在温暖地区检测到。极端，但不是全球和大多数大陆的寒冷极端。NAT 的影响在大多数陆地区域可以忽略不计。温室气体的变暖效应被 AA 的冷却效应部分抵消。两者的综合影响解释了在全球和大陆上观察到的大部分变化。