Environment and Sustainability Institute, University of Exeter, Penryn, UK.
Glob Chang Biol. 2020 Dec;26(12):7099-7111. doi: 10.1111/gcb.15336. Epub 2020 Sep 30.
The impacts of the changing climate on the biological world vary across latitudes, habitats and spatial scales. By contrast, the time of day at which these changes are occurring has received relatively little attention. As biologically significant organismal activities often occur at particular times of day, any asymmetry in the rate of change between the daytime and night-time will skew the climatic pressures placed on them, and this could have profound impacts on the natural world. Here we determine global spatial variation in the difference in the mean annual rate at which near-surface daytime maximum and night-time minimum temperatures and mean daytime and mean night-time cloud cover, specific humidity and precipitation have changed over land. For the years 1983-2017, we derived hourly climate data and assigned each hour as occurring during daylight or darkness. In regions that showed warming asymmetry of >0.5°C (equivalent to mean surface temperature warming during the 20th century) we investigated corresponding changes in cloud cover, specific humidity and precipitation. We then examined the proportional change in leaf area index (LAI) as one potential biological response to diel warming asymmetry. We demonstrate that where night-time temperatures increased by >0.5°C more than daytime temperatures, cloud cover, specific humidity and precipitation increased. Conversely, where daytime temperatures increased by >0.5°C more than night-time temperatures, cloud cover, specific humidity and precipitation decreased. Driven primarily by increased cloud cover resulting in a dampening of daytime temperatures, over twice the area of land has experienced night-time warming by >0.25°C more than daytime warming, and has become wetter, with important consequences for plant phenology and species interactions. Conversely, greater daytime relative to night-time warming is associated with hotter, drier conditions, increasing species vulnerability to heat stress and water budgets. This was demonstrated by a divergent response of LAI to warming asymmetry.
气候变化对生物世界的影响因纬度、生境和空间尺度而异。相比之下，这些变化发生的时间却很少受到关注。由于生物意义上的重要生物体活动通常发生在一天中的特定时间，因此白天和夜间之间变化率的任何不对称都会扭曲施加给它们的气候压力，这可能对自然界产生深远影响。在这里，我们确定了全球陆地近地表白天最高温度和夜间最低温度以及白天和夜间平均云量、比湿和降水的平均年变化率差异的全球空间变化。对于 1983-2017 年，我们得出了每小时的气候数据，并将每个小时分配为白天或黑夜发生。在表现出 >0.5°C 变暖不对称的区域（相当于 20 世纪表面温度变暖），我们调查了云量、比湿和降水的相应变化。然后，我们检查了叶面积指数 (LAI) 的比例变化，作为对昼夜变暖不对称的一种潜在生物响应。我们证明，当夜间温度升高超过 0.5°C 时，比白天温度升高时，云量、比湿和降水会增加。相反，当白天温度升高超过 0.5°C 时，比夜间温度升高时，云量、比湿和降水会减少。主要是由于云量增加导致白天温度下降，超过两倍的陆地经历了夜间升温比白天升温高出 >0.25°C，并且变得更加湿润，这对植物物候和物种相互作用产生了重要影响。相反，与夜间相比，白天的变暖幅度更大与更热、更干燥的条件相关，增加了物种对热应激和水预算的脆弱性。这是通过 LAI 对变暖不对称的不同响应来证明的。
