在火星的两极，冰川，从数以千计的阶层组成，是过去气候变化的证据。
At Mars' poles, glaciers, formed from thousands of fine strata, are evidence of past climatic fluctuations.
我们可以看到过去几百年里发生的气候变化。
We can see past occurrences of climate change that took place over just a few hundred years.
重建过去的气候变化是极其困难的，因为在欧洲和北美，几个世纪前才开始系统的天气观测。
Reconstructing the climate changes of the past is extremely difficult, because systematic weather observations began only a few centuries ago, in Europe and North America.
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