古气候中的沙尘变化及其气候影响

大气中的沙尘通过对太阳光的吸收和散射对地表温度产生影响,进而对大气环流和降水等也产生影响,但是在地球的不同历史时期尤其是深时地球大气中的沙尘量如何变化以及如何影响气候还有很多不清楚的地方。本文通过模式模拟对地球上4个不同时期的沙尘变化及其气候影响进行了研究,这4个时期分别是陆地植被还没有出现的前寒武时期、有植被且全球气温较高的盘古超大陆时期、大陆分布接近现代但气候较寒冷的末次盛冰期和气候较温暖的中全新世。在前寒武时期,由于陆地起沙面积大,大气中的沙尘含量可以达到现代地球的近10倍,使得全球地表温度下降也有近10 ℃。在盘古超大陆时期,由于在副热带的陆地面积比现代稍大,因此大气沙尘量也比现代稍大,对全球平均温度的影响很小。在末次盛冰期,由于寒冷干燥,沙尘量是现代的约两倍,但是它对全球有强烈的增温作用,如果没有沙尘,全球温度可能降低约2.5 ℃。在中全新世,观测显示全球沙尘量比现代少很多,模拟显示,采用现代沙尘和把沙尘全部去掉对全球平均温度的影响可以忽略,但是大西洋经向翻转流有显著变化。

Variation of atmospheric dust loading and its climate impacts in different geological periods

Dust in the atmosphere can affect the Earth's surface temperature by absorbing and scattering sunlight, and thus further affects the atmospheric circulation and precipitation. However, the mechanism of atmospheric dust loading variability and its effects on the climate during different geological periods, especially the deep time, remain unclear. This paper investigates the change of atmospheric dust loading and its climate effects during four different geological periods via numerical modeling. The four periods are the Precambrian when there was no terrestrial vegetation; the Pangea supercontinent period with terrestrial vegetation and a global temperature significantly higher than the present day; the Last Glacial Maximum with continental configuration close to the modern one but a much colder climate than the present day; and the mid-Holocene with a slightly warmer climate than the present day. Compared to the present day, the Precambrian atmospheric dust loading was nearly 10 times as much due to larger dust source area, which led to a decrease in global surface temperature by about 10 ℃. In the Pangea supercontinent period, the dust loading was slightly higher because of slightly larger land area in the subtropical zone, and its impact on the global mean temperature was small. During the Last Glacial Maximum, dust loading was about twice as much due to a colder and drier climate, yet dust had a strong warming effect—without it, the global temperature would have decreased by about 2.5 ℃. In the mid-Holocene, global dust loading was much less as shown by observational evidence, while simulation results suggest that the effect of removing global dust on the global mean temperature can be ignored for this period even as the Atlantic Meridional Overturning Circulation changed significantly.