The last time it was this warm in Wyoming was more than 6,000 years ago. It was a time when active sand dunes moved across the state and the North Platte River disappeared at its headwaters, said Bryan Shuman, an associate professor of geology and geophysics at the University of Wyoming.
Shuman spent one year studying fossil pollen buried in mud and published his long-term look at climate change in a paper in the May 2012 issue of “Climatic Change,” a journal that analyzes causes and implications of climate change.
He will present his findings at a Geologists of Jackson Hole public talk Tuesday.
Shuman’s paper involves a look at the past as well as the broader world around us, which are both topics the geologists group likes to present, said John Hebberger Jr., co-vice president of the Geologists of Jackson Hole.
“He is going to try and relate what is happening in the past to what we are seeing today,” he said. “And talk about the extent of man-made change and non-man-made change.”
Shuman has spent more than 10 years looking at natural climate changes and has published more than 50 papers on the topic.
In his paper he analyzes not only how he came to his conclusion on long-term warming, but also the possible causes. The only definitive cause that fits all possibilities is carbon emissions, he said.
He looked at three major alternatives to human-caused warming.
The first is simply warming by the sun. More than 6,000 years ago, when temperatures were similar to what they are now, the earth was actually slightly closer to the sun in the summer.
“We got more radiation from the sun and things heated up as a result,” he said. “That has not happened in the last 30 years.”
Temperatures are also warmer at night, which would not be the case if the sun caused the additional warming.
Another argument is that urban areas worsen global warming. Buildings and pavement absorb heat more than natural earth, thus warming the planet, Shuman said.
This doesn’t prove true in Wyoming, where most of the state is undeveloped.
The third and final option was natural variability in ocean and weather cycles. Shuman analyzed all data he could find from ocean changes and weather patterns such as El Nino and La Nina. No cycle pattern fit the same kind of warming Wyoming has seen in the past 30 years.
When he looked at the long-term trend data in relation to carbon dioxide emissions, the correlation fit exactly with temperature increases, he said.
While the increases in temperatures have been small — only a matter of degrees — Shuman said the outcome can be as dramatic as more forest fires and severe pine beetle outbreaks.