Weather is notoriously unpredictable. From one moment to the next, any of dozens of atmospheric variables can change to create a new weather event. In contrast, climate descriptions, which identify average and normal temperatures and precipitation levels, tend to be perceived as stable, at least over time scales that humans can easily relate to. However, that hasn't always been the case. This video segment adapted from NOVA describes climate data that suggest the Earth has undergone dramatic climate shifts in relatively short spans of time.
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