College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QE, UK
Philos Trans A Math Phys Eng Sci. 2015 Nov 13;373(2054). doi: 10.1098/rsta.2014.0421.
Climate and carbon cycle are tightly coupled on many timescales, from interannual to multi-millennial timescales. Observations always evidence a positive feedback, warming leading to release of carbon to the atmosphere; however, the processes at play differ depending on the timescales. State-of-the-art Earth System Models now represent these climate-carbon cycle feedbacks, always simulating a positive feedback over the twentieth and twenty-first centuries, although with substantial uncertainty. Recent studies now help to reduce this uncertainty. First, on short timescales, El Niño years record larger than average atmospheric CO2 growth rate, with tropical land ecosystems being the main drivers. These climate-carbon cycle anomalies can be used as emerging constraint on the tropical land carbon response to future climate change. Second, centennial variability found in last millennium records can be used to constrain the overall global carbon cycle response to climatic excursions. These independent methods point to climate-carbon cycle feedback at the low-end of the Earth System Models range, indicating that these models overestimate the carbon cycle sensitivity to climate change. These new findings also help to attribute the historical land and ocean carbon sinks to increase in atmospheric CO2 and climate change.
气候和碳循环在多个时间尺度上紧密耦合，从年际到多千年时间尺度。观测结果始终表明存在正反馈，即变暖导致碳向大气释放；然而，所涉及的过程因时间尺度而异。目前最先进的地球系统模型现在代表了这些气候-碳循环反馈，总是在 20 世纪和 21 世纪模拟正反馈，尽管存在很大的不确定性。最近的研究现在有助于降低这种不确定性。首先，在短时间尺度上，厄尔尼诺年记录的大气 CO2 增长率大于平均水平，热带陆地生态系统是主要驱动力。这些气候-碳循环异常可以作为对未来气候变化下热带陆地碳响应的新兴约束。其次，在上一个千年记录中发现的百年变率可以用来约束全球碳循环对气候波动的整体响应。这些独立的方法指向地球系统模型范围内的气候-碳循环反馈的低端，表明这些模型高估了碳循环对气候变化的敏感性。这些新发现还有助于将历史上陆地和海洋碳汇归因于大气 CO2 和气候变化的增加。
