人类巨量碳排放后果分析: 来自青藏高原综合调查的启示

人类巨量碳排放究竟导致什么后果,争议颇大,只有深入研究始新世以来大气CO₂浓度与环境变化,才有可能正确认识未来人类自身巨量碳排放之后果。大量研究揭示出: 从始新世到渐新世末期,大气CO₂浓度大幅下降,全球变冷,形成了大陆冰川; 中新世至今,大气CO₂浓度在低浓度背景之下长周期缓慢下降。当前尚不清楚何种机制主导了这一变化过程,也不清楚形成大陆冰川的水来自何方。为此,从青藏高原深部碳循环、表层水循环和环境变化的角度探讨这些问题,再分析未来人类巨量碳排放之后果。青藏高原在生长、隆升过程中,通过硅酸岩化学风化、植物光合作用、陆内俯冲(深埋)、水岩反应等方式,持续将巨量大气CO₂转化为富含碳元素的固、流体,封存在青藏高原新生的厚地壳之中,大幅降低了大气CO₂浓度,导致了全球变冷、大陆内陆(含青藏高原,下同)表层失水变干,形成了大陆冰川。渐新世—中新世之交,青藏高原生长到改变大气环流的规模,形成了亚洲季风,大陆内陆进一步荒漠化,捕获CO₂的量大幅下降,并与青藏高原内部所释放CO₂的量达到了准动态平衡,这是中新世以来大气CO₂浓度变化的主要机制。人类巨量碳排放彻底扭转了大气CO₂浓度长周期缓慢下降的趋势,大陆冰川因全球变暖所形成的液态水不会长期停留在海洋里,而以大气降水的方式重新回到干冷的大陆内陆,青藏高原将因此再次成为巨型水塔,缓解30多亿人的清洁饮用水问题。持续生长的高原和当前干冷荒漠化的大陆内陆通过前述多种方式固化人类排放的巨量CO₂,导致未来大气CO₂浓度在较高浓度背景下保持稳定,届时沙漠变绿洲,黄土高原变成有机质丰富的黑土高原,人居环境大幅改善; 但在盆地内部,PM2.5难以扩散,易形成雾霾。全球平均海平面因海水热膨胀而缓慢上升,上升速率约为1 mm/a。水主要在大陆冰川与内陆表层之间循环,与海平面升降之间没有因果关系。因此,人类巨量碳排放所导致的全球变暖对于人类自身的发展是利大于弊。

Effects of huge anthropogenic carbon emission: Inspiration from comprehensive investigations of Tibetan Plateau

The effects of huge anthropogenic carbon emission have caused huge controversy. Only by studying the change of atmospheric CO₂ levels and environment since the Eocene, can we correctly understand the consequences of human’s huge carbon emissions. Numerous studies have revealed that the atmospheric CO₂ concentrations have dropped dramatically from Early Eocene to the end of Oligocene, leading to the decrease of temperature and the formation of continental glaciers. And the atmospheric CO₂ concentrations have increased slowly in a long time under rather low and invariant levels since the Miocene. However, it is still unknown about the mechanisms which lead to the changing processes, and the place where the water that formed the continental glaciers comes from. Therefore, this research focused on the perspectives of deep carbon cycling, surface water cycling, and environmental changing of Tibetan Plateau to analyze the effects of anthropogenic huge carbon emission. During the rising process of Tibetan Plateau, with the methods of chemical weathering of silicate rocks, plant photosynthesis, intracontinental subduction (buried), and fluid-rock interactions, large amounts of atmospheric CO₂ were transferred into carbon-rich materials buried in the newly thickening crust of Tibetan Plateau. The atmospheric CO₂ levels have therefore decreased greatly, leading to global cooling and dry surface layers of the continental interiors (including Tibetan Plateau, similarly hereinafter) by losing water, and then the continental glaciers were formed. From Late Oligocene to Miocene, Tibetan Plateau had the scale to change the atmosphere circulation and the Asian monsoon was finally formed. The drastic desertification of the internal plateau began to show and the captured CO₂ decreased, which made a dynamic balance to the CO₂ from the internal Tibetan Plateau. This dynamic balance was the main mechanism of atmospheric CO₂ level change since Miocene. The long-term slow decline trend of atmospheric CO2 levels has been completely reversed by the huge anthropogenic carbon emission today. The liquid water released from the disappearing continental glaciers would come back to the cold and dry continental interiors in the form of atmospheric precipitation rather than oceans due to global warming. Tibetan Plateau would once again become a giant water tower, so that clean drinking water for more than three billion people would be substantially provided. The vast amount of CO₂ emitted by human beings would be absorbed and solidified using above methods due to the sustained growth of Tibetan Plateau and the currently dry and cold desertification of continental interiors, which makes the atmospheric CO₂ concentrations remain stably high in the future. At that time, all deserts would become oases, and the loess plateau would become a black soil plateau enriched in organic matters, which means the living environment would be greatly improved. However the PM 2.5 is difficult to spread and easy to form haze within the basin. The global mean sea level would rise due to the thermo-expansion of seawater with rate of 1 mm/a. Water will be circulated mainly between continental glaciers and inland surface layers, and has no relationship with the sea level. Therefore, the author concludes that the global warming caused by the huge anthropogenic carbon emission is more beneficial than harmful to human development.