We’re used to thinking that the weather changes – from day to day and week to week. But it’s also a fact that Earth’s climate is always changing, and it does so for fully natural reasons as well as because of man-made carbon dioxide concentrations in the air.
It wasn’t too long ago by historical standards – about the 1830s – that students of nature started to seriously think the globe had undergone revolutions in climate. The evidence for that came from Europe, where glacially polished and transported rocks dot the landscape.
By going high up into the Alps, men like Louis Agassiz studied glaciers, how they slowly flow downhill, and how they shape the land around them. Then, looking at the rocks and landscapes of Scotland and other such places, many naturalists became convinced climate had once been radically colder and glaciers had covered essentially all of northern Europe. That was disquieting news for people who had assumed that climate was an unchanging part of the world.
As the 1800s unfolded, American geologists got into the act. They mapped out glacial debris in New England, the upper Midwest, and then parts of the mountainous West. One geologist had the wit to reason that when thick glaciers covered much of the land, they must have “locked up” a great deal of water, so sea level must have been lower. Later investigations showed that to be true.
It was also during the 1800s that scientists clearly recognized how different animal species had been during the last Ice Age. Famous and exotic animals like the wooly mammoth and the saber-tooth tiger roamed the land. There were also many other lesser-known but interesting mammals, like a beaver as large as a black bear. To be sure, there were a few animals of the time we still know today, like the musk ox. But the different climate appears to have been linked to the flourishing of a number of species we simply don’t have around us today.
Early geologists couldn’t see clear reasons for climate to change – becoming bitter during the Ice Age and then warmer during our own epoch. In a step-by-step process science came to recognize two factors that probably control most climate change. One is minor but important variations in Earth’s orbit around the sun. The other is the composition of the atmosphere, including the greenhouse gases you’ve heard about.
Around 1990 there was a dramatic step forward in climate studies. Using ice cores drilled first in Greenland and then in Antarctica, scientists were able to study snow deposited in annual layers on the ice sheets, going back one year at a time like counting the rings of a tree. And the news from those studies was shocking: The evidence was clear that climate can lurch from substantially warmer to colder times (or the reverse) in just one human generation. My friends never feel I’m cheering them up when I explain the results of the polar studies, but the facts are clear: Climate changes often, and it can do so rapidly for fully natural reasons.
In my own selfish way, I just hope I’m not around for the next sudden change.