在过去的一部分时间里，人们没有温度计测温，那些研究过程就使用具代表性的数据，比如树木的年轮来衡量。

For parts of the past where there were no thermometers to consult, such studies use proxy data, such as tree rings.

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来自瑞士联邦学院的Ulf Buentgen教授和他的研究队伍从中世纪古堡和罗马城废墟中搜寻古代的木头，企图收集关于树木年轮的信息。

Ulf Buentgen and his team of researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research collected tree-ring data from ancient wood found in medieval castles and Roman ruins.

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史威特南说，为了获取巨木林中树木的年轮样本，研究人员被允许可以收集倒下树木或枯立木的横截面。

To gather samples from the Giant Forest trees, the researchers were allowed to collect cross-sections of downed logs and standing dead trees, he said.

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