Reduced sensitivity of recent tree-growth to temperature at high northern latitudes
Reduced sensitivity of recent tree-growth to temperature at high northern latitudes
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DOI：
10.1038/35596
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发表时间：
1998-02-12
期刊：
影响因子：
64.8
通讯作者：
Vaganov, EA
中科院分区：
文献类型：
--
作者：
Briffa, KR;Schweingruber, FH;Vaganov, EA
代表夏末形成的木材密度年度变化的树木年轮可以为当地夏季气温提供代理(1)。在这里，我们利用北半球高纬度数百个地点的测量结果，对大区域木材密度/气温关系进行了研究。当对北美和欧亚大陆的大片地区进行平均时，树木年轮密度系列与同一地区的夏季平均温度测量结果显示出很强的一致性，证明了该代理能够描绘次大陆甚至整个北半球的平均温度变化。在二十世纪下半叶，随着木材密度逐渐下降，木材密度和夏季气温的十年尺度趋势日益分化。木材密度对温度变化越来越不敏感的原因尚不清楚，但如果在树木气候重建中不考虑这一点，过去的温度可能会被高估。此外，最近树木对气温变化的反应减弱，这意味着基于对高纬度变暖一致敏感的碳循环模型对未来大气二氧化碳浓度的估计可能太低。
Tree-ring chronologies that represent annual changes in the density of wood formed during the late summer can provide a proxy for local summertime air temperature(1). Here we undertake an examination of large-regional-scale wood-density/air-temperature relationships using measurements from hundreds of sites at high latitudes in the Northern Hemisphere. When averaged over large areas of northern America and Eurasia, tree-ring density series display a strong coherence with summer temperature measurements averaged over the same areas, demonstrating the ability of this proxy to portray mean temperature changes over sub-continents and even the whole Northern Hemisphere. During the second half of the twentieth century, the decadal-scale trends in wood density and summer temperatures have increasingly diverged as wood density has progressively fallen. The cause of this increasing insensitivity of wood density to temperature changes is not known, but if it is not taken into account in dendroclimatic reconstructions, past temperatures could be overestimated. Moreover, the recent reduction in the response of trees to air-temperature changes would mean that estimates of future atmospheric CO2 concentrations, based on carbon-cycle models that are uniformly sensitive to high-latitude warming, could be too low.