‘Interpreting the Past to Forecast the Future’

By Robert C. Jones Jr.

‘Interpreting the Past to Forecast the Future’

By Robert C. Jones Jr.
During the Rosenstiel School’s latest Climate Café, researchers addressed methods for studying former climate conditions and how those techniques can help paint a clearer picture of what the Earth will look like.

The history of the world is recorded not only on the printed pages of books that fill the elongated shelves of massive libraries. It is also found in ice cores extracted deep from the glaciers of Antarctica and Greenland, from sediment recovered from the ocean floor, and from the rings and stumps of trees that have lived for centuries.

There, biological and chemical proxies of the Earth’s past climate—some in the form of fossils, others in the form of bubbles containing past concentrations of greenhouse gases—have been perfectly preserved, waiting to be studied by researchers in their efforts to determine what future climate will look like.

“These archives are things that we have learned to basically read as books because they tell a story,” said Larry Peterson, a professor of marine geosciences and associate dean of undergraduate education at the University of Miami Rosenstiel School of Marine and Atmospheric Science. 

Peterson—whose area of research focuses on the reconstruction of past oceans and climates, abrupt climate change, and deep-sea sedimentation processes—was one of four Rosenstiel School scientists who discussed “Interpreting the Past to Forecast the Future” on Wednesday as part of the fourth installment in the Climate Café Series.

Foraminifera, microscopic single-celled organisms found in marine environments around the world, are probably the most important of all the climate archives studied by paleoclimatologists because their calcium carbonate shells provide a fossil record that extends over the last 100 million years, Peterson said. 

“They’re very tiny, but they comprise a sizeable fraction of the sediment on the ocean floor because they live in the surface waters,” he explained. “When they die, their skeletons settle to the sea floor, and it’s from the chemistry of these skeletons that we know a great deal about past climate.”

And what foraminifera and other climate archives tell us is that over the past several millennia, our planet has undergone myriad cycles of climatic changes, conducting what Peterson called a series of natural experiments we can learn from. “At various times in the past, the Earth has been warmer than the present,” Peterson said. “We had dinosaurs that roamed in the Antarctic and palm trees living north of the Arctic Circle. At other times more recently, we’ve had great ice sheets covering large areas of the northern continents.” 

In other presentations: 

  • Peter Swart, a professor of marine geosciences who heads the Stable Isotope Lab at the Rosenstiel School, showcased how his team used a 600-year-old sclerosponge from Bahamian waters to construct a record of Atlantic Ocean temperatures dating as far back as the 14th century. Their research has shown a gradual increase in temperature to the present day. 

“So, the question is what is causing these variations?” Swart said. “There are two principal theories: one is that the changes are driven by variations in oceanic circulation. And the second one is that changes are driven by what we call atmospheric forcing—that is, changes in the atmosphere.” 

  • Hurricane Ida devastated Louisiana, Mississippi, and other southern states this past August, flooding communities, knocking out power to millions of customers, and disrupting local supply chains. Meanwhile, this year’s California wildfires have charred nearly a million acres and destroyed dozens of homes. But is the impact of extreme weather on human lives a new phenomenon? 

“The short answer is no, this is nothing new,” Arash Sharifi, adjunct professor of marine geosciences, said during his presentation on climate-human interaction over the past 300,000 years. 

In his research on the effect of climate variability on human dispersal in West Asia, Sharifi combined multiple paleoclimate records from lake sediments and cave deposits with maps of early human settlements, hypothesizing that during wet periods, humans migrated inland from coastal areas to escape flooding events that occurred hundreds of thousands of years ago. 

And by overlapping historical records of famine and drought in the Eastern Mediterranean, Mesopotamia, and Iran, Sharifi also found that such events appear to coincide with dry periods that featured excessive dust. 

  • Lisa Murphy Goes, a lecturer and climate scientist in the Department of Atmospheric Sciences, who interprets the paleoclimate proxy record, discussed climate models and how they are used to look at the drivers of past climate change. 

“We have these invaluable geological archives from all around the globe that can tell us where and when climate changed,” Murphy Goes said. “And by combining them with climate model simulations, we can help to answer why those changes occurred. It kind of feels a bit like solving a puzzle.” 

She pointed out that some scientists believe that dust from North Africa will continue to decline over the next several decades, discussing the potential impacts the decline will have on climate. “We know that it can improve local air quality, and it can also further enhance tropical North Atlantic warming, which can provide more favorable conditions for hurricane development,” she said. “But what impact is this going to have on North American rainfall? Future megadroughts, as strong as the ones that we’ve seen in the earlier Holocene [geological epoch], would have a significant impact on society, reducing water availability. Therefore, there’s a better need to be able to predict and quantify these changes in African dustiness and build better models that can represent the observed changes that we’ve seen.” 

Watch the Climate Café on the Rosenstiel School’s YouTube channel.