We have had warm periods and little ice ages; but the changes have been small.

我们有过暖期和小冰期；但是变化很小。

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At a news conference, Mathis said that in addition to the extreme warm periods, the overall year was the warmest on record.

马西斯在新闻发布会上说，除了出现几段极端温暖时期，今年还是有记录以来最热的一年。

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Warm periods were marked by gray layers in the ocean sediments caused by the calcium-containing microorganisms dissolving into acidic oceans.

暖期海洋沉积层样品因含钙微生物在酸性海洋中溶解而呈灰色。

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They tell of repeated alternations between warm periods when the pass was useable and cold periods when it was shut by the ice.

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There is clear evidence that winter storms throughout southern Scandinavia were more frequent and intense during the multi-century Dark Ages Cold Period and the much more recent Little Ice Age than either now or other comparably warm periods.

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"The stalactites and stalagmites from these caves are a way of looking back in time to see how warm periods similar to our modern climate affect how far permafrost extends across Siberia, " said Dr Anton Vaks from the University of Oxford.

BBC: Siberian cave