Wu Haibin, Guiot Joël, Brewer Simon, Guo Zhengtang, Peng Changhui
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
Proc Natl Acad Sci U S A. 2007 Jun 5;104(23):9720-4. doi: 10.1073/pnas.0610109104. Epub 2007 May 29.
The knowledge of tropical palaeoclimates is crucial for understanding global climate change, because it is a test bench for general circulation models that are ultimately used to predict future global warming. A longstanding issue concerning the last glacial maximum in the tropics is the discrepancy between the decrease in sea-surface temperatures reconstructed from marine proxies and the high-elevation decrease in land temperatures estimated from indicators of treeline elevation. In this study, an improved inverse vegetation modeling approach is used to quantitatively reconstruct palaeoclimate and to estimate the effects of different factors (temperature, precipitation, and atmospheric CO(2) concentration) on changes in treeline elevation based on a set of pollen data covering an altitudinal range from 100 to 3,140 m above sea level in Africa. We show that lowering of the African treeline during the last glacial maximum was primarily triggered by regional drying, especially at upper elevations, and was amplified by decreases in atmospheric CO(2) concentration and perhaps temperature. This contrasts with scenarios for the Holocene and future climates, in which the increase in treeline elevation will be dominated by temperature. Our results suggest that previous temperature changes inferred from tropical treeline shifts may have been overestimated for low-CO(2) glacial periods, because the limiting factors that control changes in treeline elevation differ between glacial and interglacial periods.
热带古气候的知识对于理解全球气候变化至关重要，因为它是最终用于预测未来全球变暖的大气环流模型的试验台。一个长期存在的关于热带地区末次盛冰期的问题是，从海洋 proxy 重建的海面温度下降与根据树线海拔指标估计的陆地温度在高海拔地区的下降之间存在差异。在本研究中，基于一组覆盖非洲海拔范围从海平面 100 米至 3140 米的花粉数据，采用一种改进的反演植被建模方法来定量重建古气候，并估计不同因素（温度、降水和大气 CO₂ 浓度）对树线海拔变化的影响。我们表明，末次盛冰期期间非洲树线的降低主要是由区域干旱引发的，尤其是在高海拔地区，并且大气 CO₂ 浓度的降低以及可能的温度降低进一步加剧了这种情况。这与全新世和未来气候的情景形成对比，在全新世和未来气候中，树线海拔的升高将主要由温度主导。我们的结果表明，对于低 CO₂ 的冰期，先前从热带树线变化推断出的温度变化可能被高估了，因为控制树线海拔变化的限制因素在冰期和间冰期有所不同。
