NOAA/WDS Paleoclimatology - Klesse - XEP - PINI - ITRDB GRC034

The Mediterranean region has been identified as a global warming hotspot, where future climate impacts are expected to have significant consequences on societal and ecosystem well-being. To put ongoing trends of summer climate into the context of past natural variability, we reconstructed climate from maximum latewood density (MXD) measurements of Pinus heldreichii (1521–2010) and latewood width (LWW) of Pinus nigra (1617–2010) on Mt. Olympus, Greece. Previous research in the northeastern Mediterranean has primarily focused on inter-annual variability, omitting any low-frequency trends. The present study utilizes methods capable of retaining climatically driven long-term behavior of tree growth. The LWW chronology corresponds closely to early summer moisture variability (May–July, r = 0.65, p < 0.001, 1950–2010), whereas the MXD-chronology relates mainly to late summer warmth (July–September, r = 0.64, p < 0.001; 1899–2010). The chronologies show opposing patterns of decadal variability over the twentieth century (r = −0.68, p < 0.001) and confirm the importance of the summer North Atlantic Oscillation (sNAO) for summer climate in the northeastern Mediterranean, with positive sNAO phases inducing cold anomalies and enhanced cloudiness and precipitation. The combined reconstructions document the late twentieth—early twenty-first century warming and drying trend, but indicate generally drier early summer and cooler late summer conditions in the period ~1700–1900 CE. Our findings suggest a potential decoupling between twentieth century atmospheric circulation patterns and pre-industrial climate variability. Furthermore, the range of natural climate variability stretches beyond summer moisture availability observed in recent decades and thus lends credibility to the significant drying trends projected for this region in current Earth System Model simulations.

地中海地区已被确认为全球变暖热点区域，未来气候影响预计将对社会与生态系统福祉造成显著后果。为将当前夏季气候趋势置于过去自然变率的背景之中，本研究基于希腊奥林匹斯山的海尔德奇松（Pinus heldreichii，1521–2010年）的最大晚材密度（maximum latewood density, MXD）测量数据，以及黑松（Pinus nigra，1617–2010年）的晚材宽度（latewood width, LWW）数据重建了气候记录。此前东北地中海地区的相关研究主要聚焦于年际变率，忽略了各类低频趋势。本研究采用了能够保留树木生长受气候驱动的长期特征的分析方法。其中，晚材宽度年表与初夏水分变率（5–7月，相关系数r=0.65，p<0.001，1950–2010年）高度相关，而最大晚材密度年表则主要与晚夏气温（7–9月，r=0.64，p<0.001；1899–2010年）相关。两类年表在20世纪呈现出相反的年代际变率模式（r=-0.68，p<0.001），并证实了夏季北大西洋涛动（summer North Atlantic Oscillation, sNAO）对东北地中海夏季气候的重要性：正相位的夏季北大西洋涛动会引发冷异常，同时增加云量与降水量。联合重建结果记录了20世纪末至21世纪初的变暖变干趋势，但表明在约公元1700–1900年期间，该区域总体呈现初夏更干燥、晚夏更凉爽的气候特征。本研究结果显示，20世纪的大气环流模式与前工业化时期的气候变率之间可能存在解耦现象。此外，自然气候变率的范围超出了近几十年观测到的夏季水分可利用性区间，因此为当前地球系统模型（Earth System Model, ESM）模拟中该区域预计出现的显著变干趋势提供了可信度支撑。