Nothing about Earth history is static or unchanging. That’s particularly true of climate, and thereon hangs more than one interesting tale, including recent news of a scientific advance in understanding how past climate has changed.
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It wasn’t too long ago by my standards – about the 1830s – that naturalists started to seriously think the globe has 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 Germany, Scotland, and other such places, many naturalists started to become convinced climate had once been radically colder and glaciers had covered essentially all of northern Europe. That was disquieting news for people who had always assumed that climate was an unchanging part of the world.
As the 1800s unfolded further, 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. The oceans control many aspects of climate, but when conditions are cold enough to produce worldwide glaciation, sea level is strongly affected by climate.
It was 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 mammals of the time, like a beaver as large as a black bear. There were a few animals 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. We didn’t doubt the radical evolution of climate change, but at first it just wasn’t clear what could be driving the alterations that clearly had important effects for Earth history. 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.
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 in time one-by-one like rings of a tree. And thenews from those studies was shocking: the evidence was clear that climate can lurch from warmer to colder times in just one human generation.
Some new research takes up the tale of climate change with reference to what likely caused the extensive ice sheet in Antarctica to form. That enormous repository of ice came into being about 34 million years ago and has been influencing climate ever since.
New evidence from researchers at Yale and Purdue published in Sciencemagazine suggests that a 40 percent drop in carbon dioxide concentrations in the ancient atmosphere was the driving force that led to the formation of the Antarctic ice sheet. In a span of 100,000 years the whole region around the South Pole was transformed.
At this point, science can’t tell us what made the carbon dioxide levels drop. That’s the next question that needs to be investigated. But it’s crystal clear that climate is a dicey business, one from which we should expect change in both specific regions and all over the globe.
We may not like how fragile Earth’s climate looks. But the more we know about even natural climate evolutions, the more it seems clear change is in the cards.
Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.