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AAAS Fellow Kim Cobb “Listens to the Rocks” to Understand Climate Change

headshot of AAAS Fellow Kim Cobb
AAAS Fellow Kim Cobb, Ph.D. Photo credit: John Amis/AP Photo.

At a glance, AAAS Fellow and climate scientist Kim Cobb’s research expeditions sound like the plot of an adventure series – from diving into the tropical Pacific for coral samples to trudging through the caves of Borneo gathering fallen stalagmites. Each specimen she collects conceals within its chemical structure a detailed history of tropical temperatures over the course of millennia.

“We’re getting closer to their truth,” says Cobb, whose field of paleoclimatology leverages the geological record to understand climates from before the availability of formal measurement.

As oceans regulate the global climate, their majestic inhabitants – coral reefs – are the silent historians of the sea, locking data about past water conditions into their calcium-carbonate skeletons. It’s Cobb’s job to crack their code – “listen to the rocks,” she says. Her lab uses uranium-thorium dating to determine the age of coral samples, and then analyzes them for the ratio of two oxygen isotopes – a ratio reflecting water temperature at the time of formation.

“All the best machinery in the world is still unable to capture the full beauty and detail of the record coral has locked into its skeleton,” says Cobb, a professor in the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.

While most coral-based climate reconstruction focuses on the last two centuries, Cobb uses cutting-edge technology to push the envelope. Some of her team’s research of long-dead samples strewn along the shoreline paints a timeline of climate trends and extremes dating back 7,000 years. Tapping into this rich archive helps scientists build computer models of future climates that include projections of climate extremes.

One such phenomenon – El Niño – sits at the core of Cobb’s more than 20-year research career. During an El Niño event, the surface water in the Pacific Ocean near the equator becomes warmer than usual. The warm water, in turn, alters the atmosphere and prompts extreme weather patterns around the world. The U.S. Gulf Coast and Southeast get heavy rain and flooding, while the northern U.S. and Canada experience dryer than normal conditions.

El Niño events devastate coral reefs – a sobering reality Cobb has helplessly encountered in her years-long research at a site off Kiritimati Island (also known as Christmas Island). The size of the average El Niño event has increased in recent decades, as compared with the pre-industrial era, pointing to a possible link with human-caused climate change, Cobb says.

When one such strong event was on the horizon in the summer of 2015, she coordinated several expeditions to the reef she had been studying.

“We are very far from where El Niños grow, develop and decay,” she explains. “You have to plan these expeditions months in advance. You’re literally keeping your finger on the pulse of what the tropical Pacific is doing at any given moment.”

After months of record-breaking temperatures, the reef succumbed to bleaching, a process by which corals expel the algae living within their tissue and turn completely white. Eventually, Cobb says, 85 percent of the reef was dead.

“It’s something I never thought would happen in my lifetime,” she said. “To bear eyewitness to it in slow motion over several expeditions was something I was unprepared for.”

This shellshock of the reef’s decimation – mixed with the political climate at the time – forced Cobb into more conversations defending science in the public eye. In 2016, an era of rhetoric “openly hostile to climate science” began, Cobb says. Around that time, Cobb’s efforts to demonstrate the impact of climate change pivoted to advocating for ways to solve the problem.

“Most people understand there’s a catastrophic trend afoot in terms of our emissions and what it means for the climate around the world,” Cobb says. “People are moving very quickly to wanting to understand the solutions-side of the equation.”

As part of her recent work, Cobb has engaged in several solutions-based research projects, including Drawdown Georgia, an effort to identify high-potential strategies to cut the state’s carbon footprint. Another project focuses on urban heat islands – neighborhoods, often low income, that experience higher temperatures compared to outlying areas. Higher temperatures translate to higher rates of heat-related deaths and illnesses.

“Future climate change impacts vulnerable communities around the world,” Cobb says. “Learning what we can about the threats today and what those mean for tomorrow is extremely exciting and allows me to see that there is a way for the geosciences to play a key role in solutions making.”

In addition to participating in AAAS’ What We Know initiative – a blue-ribbon panel designed to uplift climate research – Cobb was a lead author on the sixth Intergovernmental Panel on Climate Change (IPCC) report released in August 2021. The IPCC, assembled by the United Nations, monitors and assesses global science related to climate change.

Over three years, Cobb worked with more than a dozen scientists to craft the report’s first chapter. In total, the document has 12 chapters drafted by hundreds of experts.

“I played a very small role, but it’s obviously something I’m honored to have been a part of,” Cobb says. “It really broadened my view of what is going on across climate science in fields I would normally never be exposed to.”

Cobb calls her participation a “once in a lifetime experience” – literally. “I mean that,” she adds, laughing. “I’m never doing that again.” Admittedly, she says, working on the report proved grueling and exhausting yet worthwhile in the fight to preserve Earth’s splendor for future generations.

“These places are exceptionally beautiful. Just being a part of those ecosystems for a couple weeks and getting to know them intimately over decades of sustained work is immensely rewarding to me,” Cobb says. “I will die trying to make sure these precious places are preserved in character and function for generations to come.”