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Scientific (r)evolution, continued

Cause and effect

Bryson’s ideas about climate were gaining traction as part of a broader recognition that people were altering the planet on a scale never seen before. Widely considered one of the world’s leading climate scientists, he testified before Congress on the issue in 1974.

But he was not focused on global warming, even as greenhouse gas emissions were beginning to be seen as a potentially serious issue among other scientists. He remained an outspoken advocate of the idea that humans were causing a lot of changes, and that global cooling was also possible due to rising levels of aerosols – particles or droplets of pollution from combustion and industrial activity.

1974 Wisconsin State Journal article on Reid Bryson research
A 1974 Wisconsin State Journal article reports on
Bryson's research into the agricultural risks of
climate change. Image courtesy UW-Madison Archives.

In 1977, in the midst of his federally funded Climate and Food Project, Bryson published Climates of Hunger: Mankind and the World’s Changing Weather, in which he and co-author Thomas Murray argued that climate change driven by aerosols was causing shifts in rain belts and agricultural regions, leading to starvation. The book, written for a popular audience, sold well and echoes today in the public discourse over climate change and food security.

Kutzbach, too, was engaging in the growing international conversation about global change, but from a different perspective. He was invited to serve on a National Academy of Sciences committee to assess the scientific basis for climate change resulting from anthropogenic carbon dioxide emissions.

The groundbreaking 1979 “Charney report,” as it is often called, “really put the finger on carbon dioxide as a very important consideration for future climates,” says Kutzbach. Its comprehensive review of the state of climate modeling and the potential for models to test hypotheses about the causes of climate change was deeply influential to policy makers and the scientific community, setting research agendas for the following decade.

“There had been a national emphasis on developing a high-quality climate model that would mimic the behavior of the world and allow you to do, in a sense, laboratory experiments for the first time,” he says. “What happens if we change carbon dioxide? What happens if we change aerosols? We could then compare that with the data.”

Kutzbach says climate models, along with the parallel development of satellite observation capabilities, were reaching a point where they could produce plausible results – especially when they could prove their validity by reproducing the past. Kutzbach was the first to use these powerful computer models as quantitative tools to investigate climate history.

“The bulk of the climate community was thinking of climate models as a way to simulate the present, year-to-year variability, and to look at the future,” he explains. “But I was fascinated to look backward, to ask, ‘What did cause ice ages? What caused the Sahel to be wet 6,000 years ago?’ Models could help quantitatively answer those kinds of questions.”

Proving the past

Kutzbach was also the first to use models to verify that slow “wobbles” in the Earth’s orbit – manifested in the shape of its orbital path and in the angle and orientation of its axis – were primary drivers of climate change over thousands of years, a phenomenon first known as Milankovitch cycles. These cycles, it turned out, drove both the advance and retreat of ice sheets in the high latitudes and the waxing and waning of monsoonal rain in the subtropics. 

Research image of fossil pollen
CCR was at the forefront of paleo-
climatology, or the study of past
climates. Ancient spruce pollen
image courtesy UW-Madison Archives.

“These variations would change seasonal sunlight that could, on the one hand, make the monsoons stronger,” he says. “If you had warmer summers, you’d get strong monsoons. But if you had really cold summers, you had the chance that snow cover wouldn’t melt in Canada and you might begin to build up ice ages.”

The idea that orbital variations might cause ice ages was proposed as early as the 1870s, but Kutzbach was the first to test it quantitatively – pioneering work that would later see him elected to the National Academy of Sciences. “We were able to show that these orbital variations are a big enough factor to account for the large-scale climate changes of the last million years,” he explains.

Paleoclimatology – the study of past climates – was a fast-growing field, and CCR was at the forefront, building on the interdisciplinary foundation laid by Bryson.

In 1977, Kutzbach and Thompson Webb, a Bryson Ph.D. student who went on to his own illustrious career at Brown University, came up with an idea that would put CCR at the center of the first “big science” project in paleoclimatology. They landed a major grant from the National Science Foundation and U.S. Department of Energy to characterize and map global climate, vegetation and hydrological changes spanning 21,000 years, since the peak of the last ice age.

The Cooperative Holocene Mapping Project (COHMAP) was an enormous undertaking, involving nearly 50 scientists at five universities. They set out to reconstruct and map the past climate using evidence such as fossil pollen, marine plankton and lake sediments, creating snapshots at 3,000-year intervals in locations around the planet.

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