who study climates of the past, know that Earth's climate was not as
stable for our ancestors as it has been for us.
These abrupt, harsh changes could mean life or death, often forcing
whole populations to move if they wanted to survive.
For example, one well-studied event 8,200 years ago was a sudden cold
shift that lasted over a century, recorded in Greenland ice cores and
within the fossil record across Europe, the researchers said. It
occurred when the North American ice sheet decayed after the last ice
age and released meltwater into the North Atlantic Ocean, disrupting
the currents that brought heat to Western Europe. This triggered
large-scale population crashes in northern Britain and large cultural
changes in southern Europe, they said.