Warming in the Age of Pangaea: A Prequel?
Discovery News, Sept. 7, 2007
Sept. 7, 2007 The emerging story of a global climate shift a third of a billion years ago seems to be a prequel to what climate scientists expect from the current trend in global warming.
Using the same sort of Global Circulation Models as those which predict climate change today, University of Michigan researcher Christopher Poulsen and his colleagues have reproduced what might have happened on the supercontinent Pangea in the late Paleozoic era, about 300 million years ago, when the polar ice melted.
"During this time you see all kinds of environmental changes," said Poulsen, referring to the fossils and chemical evidence left in rocks.
Temperatures spiked at the equator and plants' ranges were changing quickly. There were at least three major advances of ice sheets at high latitudes, followed by thaws.
"The question is," he added, "How much can these ice sheets influence changes in the tropics?"
One way to try and answer that question is with a climate model.
The researchers set up a climate model for the late Paleozoic Earth in the same way climate scientists use them for todays Earth. The main difference is that no one has a lot of detail about the height of all the mountains and the exact details of geography in the Paleozoic. So the model was necessarily coarser than those used for the modern Earth, Poulsen explained.
"So we ran these experiments and found we were able to get quite dramatic changes," Poulsen told Discovery News.
They showed that melting of large to moderately-sized high-latitude ice sheets resulted in a reversal of tropical trade winds and big expansions of low-latitude desert areas into what had been warm temperate forests. Their report appears in the September issue of the journal Geology.
Another possible similarity between what happened in the Paleozoic and what is occurring today is the relationship that carbon dioxide has with warmer times. When carbon dioxide was high, ice sheets were small, and vice versa. Its the same relationship seen over the past million years, he said.
"This is not a perfect analogue" to Earths climate today, said Poulsen. "Its just further evidence that these types of changes in carbon dioxide and glaciation lead to enormous changes."
The Paleozoic climate model is also a new way for geologists to look into the past, or at least to try to make sense of the climatic clues left behind in the rocks.
"It can be very helpful in driving research directions," said geologist Neil Tabor of Southern Methodist University. Tabor also works on reconstructing the Paleozoic climate but without the aid of climate models. His tools are telltale fossils, sediments and stable isotopes in minerals that reveal things like past carbon dioxide levels in the atmosphere.
"My work is really incapable of addressing what was responsible for climate changes," said Tabor. Modeling pushes the geological data to the next level, and is helpful in studying todays climate.
"In order to see how (carbon dioxide) drives climate and flips from ice house to a greenhouse, it is very useful," said Tabor.