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This is Scientific American's 60-second Science, I'm Julia Rosen.
How much colder was it at the peak of the last ice age? That's a question scientists have been trying to answer for decades.
And now they have a new best guess: 11 degrees Fahrenheit.
That's a lot, especially considering it's a global average. Parts of North America were much colder.
"First of all, large areas of the northeast were completely under ice.
So that would have been pretty chilly; you wouldn't be living there.
But even here in the west, right, where we weren't covered by an ice sheet, it would have been something like 20 degrees Fahrenheit lower."
Jessica Tierney, a paleoclimatologist at the University of Arizona.
Tierney and her colleagues spent years compiling information about Earth's climate at the height of the last glacial period, about 20,000 years ago.
"We obviously don't have thermometers in the glacial period, so we have to instead look for these kinds of stand-in indicators."
One kind of stand-in is plankton that lived in the ocean and got preserved in marine sediments.
Scientists use these fossils to infer past ocean temperatures by studying changes in the chemistry of their shells and in the kinds of fats and other compounds they produced.
Tierney and her team then combined these data with a climate model to give a full picture of glacial conditions.
"It's actually a technique used every day in weather forecasting. What's new is we're using it for the past, not the future.
So we are actually, you know, hindcasting, if you will, rather than forecasting."
这里是科学美国人――60秒科学系列,我是朱莉娅・罗森。
在上一个冰河世纪的顶峰时期,气温比现在低多少?这是科学家数十年来一直试图回答的问题。
现在他们有了新的最佳猜测:11华氏度。
温度相差很多,尤其是考虑到这是全球平均水平。北美部分地区要冷得多。
“首先,东北部大片地区完全被冰覆盖。
所以会相当寒冷;人们不会住在那里。
但即使在未被冰层覆盖的西部,气温也会低20华氏度左右。”
亚利桑那大学的古气候学家杰西卡・蒂尔尼说到。
蒂尔尼和同事花费数年汇编了大约2万年前最后一次冰河时期高峰时的地球气候信息。
“显然,在冰川时期我们没有温度计,因此我们必须寻找这些替代指示器。”
其中一种替代物是生活在海洋中并保存在海洋沉积物中的浮游生物。
科学家利用这些化石,通过研究它们外壳中化学物质、脂肪类型以及它们产生的其他合物的变化,来推断过去海洋的温度。
随后,蒂尔尼和团队将这些数据与气候模型结合起来,提供了冰川环境的全貌。
“这实际上是一种每天都在天气预报中使用的技术。不同的是,我们用它来推断过去,而不是预测未来。
可以说,我们实际上是在后报,而不是预测。“
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