A study of historic plant pollen by a University of Wyoming geophysicist and his students revealed that only 70 years in the past 11,000 may have produced average temperatures as high as those observed in North America over the last decade.
The research was laid out in a paper, “Reconciling Divergent Trends and Millennial Variations in Holocene Temperatures.”
Published Wednesday in the science journal Nature, the study joins the volume of research pointing to a current, rapid warming trend that is counter to the historic norm of a gradually warming and cooling planet.
Additionally, the researchers say that without human beings and their various activities, the average temperature would be falling now. It is not, said Bryan Shuman, professor in the Department of Geology and Geophysics, and co-leader of the study.
For Wyoming, a state economically wedded to fuels that contribute to this change, such as coal burned for electricity, this kind of research is valuable in understanding what is happening in the climate, and what Wyoming’s response will be, the professor said.
“To me that’s one of the motivations for studying this,” he said of researching long- and short-term changes in climate. “What are those natural ups and downs? How big are they and how long do they take? What are their causes?”
The researchers came to their results in two ways. They took fossil pollen samples at more than 600 sites in North America and Europe, including lakes in the Big Horn Mountains and ponds in Yellowstone National Park.
Certain plants survive at different temperatures, producing a band of possible temperature averages. They narrowed that band dramatically by taking fossil pollen samples from some 60 different types of plants, said Shuman, the UW professor.
The pollen approach was also used to predict current average temps, a way to gauge the accuracy of this type of study in real time. It worked very well, he said.
The pollen studies could give the researchers reliable century-averages going back thousands of years. But they needed more.
“What’s much harder to do, would be to know if tucked into one of those centuries or decades is an individual year or decade that was really warm,” he said.
So they added numbers from the National Center for Atmospheric Research’s climate model to narrow the average temperatures further.
The modeling from the center provided estimated temperatures down to the hour.
The results of the pollen research and the climate modelling available were encouragingly parallel, the professor said.
“I was stunned actually, how similar that forecast of the past from the model was to our reconstruction,” he said.
But what stands out to Shuman about the results is just how dramatic the recent shift to warming has been, bucking a long trend of slow decline in average temperatures.
The temperature is obviously warmer than it was 11,000 years ago, the end of the last ice age, Shuman said. But around the time that the Ancient Egyptian civilization was on the rise, the average temperature was actually declining, in gradual, marginal steps.
We should be following that slow curve for thousands of years, if history is to be repeated. Instead, the average temperature is going up, and one-third of that temperature rise has taken place over a very short period of time for a geologist: the last 30 years, he said.
With the industrial age, humans changed the composition of the atmosphere, he said.
This isn’t new information. Adding carbon dioxide to the atmosphere is like putting on a coat, he said.
“We’ve also known since the 1800s that gasses like carbon dioxide are very effective at trapping heat,” he said. “The basic physics of it? We’ve turned on the heat.”
Climate change studies have been increasingly political in recent years, nowhere more so than Wyoming, the largest producer of coal in the country.
It’s understandable that the debate over climate change is so political, he said. But the science shouldn’t be that way, he added.
“As somebody here in Wyoming I recognize that our state really relies on a vibrant economy and an economy tied to fossil fuels,” he said.
The state will have to respond to how climate science is changing the global approach to those traditional fuels, he said.
“I think that science is influencing (those) decisions elsewhere,” he said. “We should pay attention to it, so we can be informed about our own economic decisions looking towards the future.”
Other contributors key to this study came from the University of Oregon, the University Utah and the U.S. Geological Survey of Corvallis, Oregon. Jeremiah Marsicek, a U.W. Ph.D. graduate, worked on the study from 2011 to 2016. He was lead author of the paper published Wednesday.