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Taking The Geologic View Of Climate Change

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With headlines proclaiming that climate change is coming – seas may rise and cities may flood, crops may fail and people may be displaced – nothing seems stable about the state of the planet. But geologist Robert Gregory has taken the long planetary view of Earth’s geological and climate cycles. In short, he sees the Earth as extremely stable when compared with other alternatives in our solar system. “We worry about the state of Earth and how climate is changing,” says Gregory, professor and chair of the Roy M. Huffington Department of Earth Sciences in Dedman College. “But the underlying cycles have been similar for 3.5 billion years, and I assure you that Earth is very stable in the long term. We know, however, that climate fluctuations occur.” Areas of the planet that were abnormally hot – or cold – change in size from time to time, he says. These fluctuations are not symptoms of major instability; in fact, they are normal.

“The problem is that civilizations are not good at adjusting to climate change, especially now,” he explains. “In the old days, it was easier for civilizations to pick up and move when the climate shifted. Humans could follow the warmth and flee the flooding or the cold. But now, with human population near the carrying capacity of the planet and humans having the ability to affect global climate change, it is not so easy.” Gregory, who earned his Ph.D. from the California Institute of Technology, has spent his career studying how the Earth works, especially global geochemical cycles and plate tectonics – the interaction between rocks and fluids in the crust and mantle. He was one of the first scientists to understand how deep seawater circulation penetrated into the mantle as a result of crust formation at mid-ocean ridges by using the oxygen isotope ratios in 100-millionyear- old ocean crustal rocks. These oxygen isotope ratios contain a “memory” of when they first came into contact with seawater millions of years ago.

With their understanding of plate tectonics expanding, Gregory and other researchers took a second look at what was occurring on and below the ocean floors and how it affects the chemical composition of the oceans and the atmosphere. Carbon dioxide and water and their interaction with rocks driven by plate tectonics provide a “thermostatic control” of Earth’s climate by regulating the carbon dioxide content of the atmosphere. In addition, the chemistry of the oceans is regulated, much as the kidneys help cleanse and regulate the salt content of blood in the human body, providing a stable environment for life to evolve, Gregory says. “It is no accident that the medical profession uses saline solution with seawater salinity.” As Gregory continues to study stable isotopes to find more clues about the planet’s future by unlocking the past, he and his SMU Earth Sciences colleagues Crayton Yapp and Neil Tabor remain confident about the general stability of the Earth over geologic time. “However, the big concern this century is human activity that is perturbing the carbon cycle at unprecedented rates,” he says. “For the short term, energy and climate are tied together and both will affect the future quality of life.”

For more information: smu.edu/earthsciences/people/ faculty/gregory.asp