Kim Cobb: Corals, Climate, and a Changing World

Kim Cobb. Courtesy of Georgia Tech

The loss came as a shock for climatologist and AAAS member Kim Cobb. As a leading expert on El Niño — that unpredictable disrupter of global climate and weather that devastated her research subject — Cobb was uniquely qualified to comprehend what she was seeing. Digesting the loss intellectually was the easy part. Coming to grips with the loss emotionally would take time, but it would change her life, leading the scientist to lower her carbon footprint and become politically active.

Cobb came face to face with the devastated reef in April 2016 while on a research expedition in the tropical Pacific. Peering through the saltwater lens of the ocean to the crystalline structures some 40 feet below, Cobb, the expedition’s leader, saw a nearly ubiquitous wash of red-brown color. Missing was the lively rainbow spectrum she had come to know and love on her many trips to this part of the world.

Instantly, her mind registered what she was seeing: the coral reef was nearly gone, having succumbed to the abnormally warm waters of the previous year’s exceptionally powerful El Niño. Left behind were the red-brown colors of algae that had grown over the dead corals. Maybe five percent of the reef survived, according to Cobb. She was shocked, but not surprised.

“It was a very clear turning point for me,” remembered Cobb from her office at the Georgia Institute of Technology where she runs a lab specializing in the paleoclimatology, the study of our planet’s distant past.

For nearly two decades Cobb’s research has focused on unraveling the mystery of El Niño and La Niña events and how they have changed over time. Using oxygen isotopes and decaying uranium locked away in living and fossilized coral, Cobb and colleagues have revealed an intermittent record of El Niño and La Niña events going back 7,000 years.

This impressive dataset and the research that has revolved around it has helped inform the scientific community’s understanding of El Niño and La Niña events as well as just how rascally the sibling climate phenomena can be.

El Niño and La Niña are the extreme phases of a larger, naturally occurring climate pattern called the El Niño Southern Oscillation (ENSO). El Niño is ENSO’s warm phase. La Niña its cool phase. ENSO originates in the tropical Pacific, showing up in the historical and paleoclimate records as either abnormally warm water (El Niño) or abnormally cool water (La Niña) in the tropical Pacific.

In the oxygen isotopes extracted from coral, the shift in ocean temperatures comes through as a clear signal: lower oxygen isotopes for the El Niño phase; higher oxygen isotopes for the La Niña phase. Why fluctuating Pacific Ocean temperatures matter is simple: what happens in the tropical Pacific does not stay in the tropical Pacific.

ENSO is notorious for influencing and disrupting climate and weather the world over, producing impacts as divergent as droughts and downpours, famines and floods.

“There’s basically nowhere on our planet that doesn’t register the impacts of ENSO extremes, either El Niño or La Niña. It matters profoundly to society, and not only to society but to ecosystems more generally,” said Cobb.  

But for Cobb there is another reason to investigate ENSO. As an object of study, ENSO has been notoriously hard to simulate in computer models, and hence extremely difficult to predict. On top of all that, ENSO appears to be changing, responding in its own unpredictable way to climate change.

The El Niño that occurred over the winter of 2015/2016 and devastated the coral reef Cobb was researching is part of a clear trend revealed in large part by Cobb’s research: El Niño events have grown in power since pre-industrial times, a growth that could be linked to anthropogenic, or human-caused, climate change. However, Cobb is quick to point out, there is still a lot of uncertainty and what ifs associated with ENSO. For Cobb, this makes the climate pattern an irresistible and imperative research topic.   

“From a basic research perspective, [ENSO] is very interesting. It just leaps out of nothing and then slaps us in the face every couple of years,” said Cobb.

Cobb first traveled to the tropical Pacific during the El Niño year 1997, having already contracted the ENSO research bug while studying sea floor sediment off the coast of Santa Barbara, California. Her destination: the Palmyra Atoll, a central Pacific island chain located roughly due south of the Hawaiian Islands.

“The phrase, ‘love at first sight’ comes to mind. I instantly fell in love with those islands,” said Cobb, remembering the trip. 

A graduate student at the Scripps Institution of Oceanography, Cobb had tagged along on an expedition run by the scientist Richard Fairbanks, an oceanographer who helped pioneer the use of isotope chemistry to reconstruct climate records.

As their vessel pulled alongside a paradisiacal island, the more experienced researcher took the novice Cobb aside, asking her if she knew what those gray rocks were lining the beach. Cobb admitted that she did not. That’s when Fairbanks told her the “rocks” were actually fossilized corals, containing an as yet untapped archive of past ocean temperatures.

Later, Cobb would learn to use an oversized core bit attached to an oversized drill and a fair amount of elbow grease to core-out six-foot long samples from the vast fossilized remains lining the beaches of the islands around her. From these and living coral in the nearby waters she would extract the isotopic temperature records and steady time-keeping afforded by decaying uranium. Later on, in an effort to find still more paleoclimate archives, Cobb would travel to Borneo. There in the dense forest she would explore caves, extracting paleoclimate proxy records from millennia-old stalagmites. The result, after years of effort, would be her dataset going back 7,000 years, a chronicle of ENSO’s stormy history.

Yet when she first went to the tropical Pacific in the late 1990s, hardly anybody was looking into ENSO’s paleoclimate record in the central Pacific.

“You might want to think about that,” was Fairbanks’ final comment to Cobb as she stared out at the rocks and her future. The exchange took maybe 15 seconds. When she got back to the States, Cobb set about figuring out what it would take to unlock and study the coral ENSO record.

“That was when I began to understand the complexity of the oceanography and what powerful recorders were present all over these islands in the form of corals,” said Cobb. “There was this raw, untapped scientific potential. Hardly anybody was working at these places.”

Thanks to Cobb and others in her field, we are now closer than ever to understanding ENSO and how it might be altering as our climate changes. One huge takeaway from Cobb’s work: ENSO is highly variable.

In a series of papers going back to the early 2000s, Cobb outlines how ENSO has changed over the Holocene. Perhaps the clearest description of this history came in a 2013 paper led by Cobb in the journal Science. Using her meticulously collected data, Cobb was able to show that ENSO fluctuates, sometimes wildly, between its El Niño and La Niña phases.

What’s more, by making a comparison between the coral record and a computer simulation of ENSO, Cobb and her fellow researchers were able to conclude that much of this change is due to ENSO’s inner workings, the climate pattern’s internal variability. Over the paleoclimate record, this internal variability proved to be a greater force for change than any external forcing, such as insolation changes caused by Earth’s orbit. This complicates our understanding of how anthropogenic climate change might alter ENSO.    

Abundant data confirm that extra trapped energy from the sun due to greenhouse gases added by humans is essentially driving, or forcing, climate change. Climate phenomena that respond predictably to this added forcing — such as rising air temperatures or disappearing mountain snow — are predictable in large part because they are linked to added greenhouse gases through relatively simple dynamics. Add more carbon dioxide to a real or simulated climate system and expect air temperatures to go up.

ENSO and other phenomena with lots of internal variability and lacking a clear sensitivity to past climatic “forcings” are another story all together. They are very hard to model, in part because we have so few records of the phenomenon that predate the 20th century. But this doesn’t mean that we’re not getting closer to understanding ENSO.

In that same 2013 paper, Cobb and colleagues point to an emerging trend in their data: 20th century ENSO activity was measurably stronger than that of the pre-industrial era. Three years later, Cobb would experience ENSO’s growing intensity first hand as she swam through the remains of the reef, a latticework of loss that struck the normally optimistic scientist to her core. The El Niño event of 2015/2016 was one of the three largest since record keeping began roughly 50 years ago and is comparable to some of the largest El Niño events seen in the paleoclimate record.

What is clear, according to Cobb, is that ENSO is occurring in a changed global climate and that means the base conditions of the phenomenon are changing. 

“What is emerging as a point of significant scientific progress is that El Niño events are happening in a changed state,” said Cobb.

This means that while we are still grappling with understanding ENSO’s many moving parts, we are getting closer to saying how these parts are beginning to respond to climate change. Yet regardless of how climate change might affect ENSO, Cobb said that many of the impacts of ongoing climate change are clear and well-supported by science. This makes it imperative, she said, that we act now, a message she has taken to heart.

In December 2016, Cobb was in San Francisco at the annual meeting of the American Geophysical Union, the nation’s largest association of Earth scientists. Still reeling from the loss of her reef the previous spring and the unexpected results of the U.S. presidential election, on the second day of the conference, Cobb and a small group of climate researchers held an impromptu protest. Donning white lab coats, they spoke their minds about climate change research and the political obstacles it frequently faces. Cobb took the microphone, sharing her story about the lost reef. She didn’t prepare her remarks. She just spoke from her core.

“That was the first time I felt called and compelled to stand up and say things that I have never said before and in a way that felt very vulnerable and terrifying at the time but absolutely necessary, absolutely unavoidable,” said Cobb.

Speaking at the conference was the start of something for the researcher. She would go on to speak at a March for Science in Atlanta, Georgia. She’s also taken significant steps to lower her and her family’s carbon footprint. She’s become a bike commuter and a vegetarian. She’s cut out plastics. And she talks with her four kids about climate change.  

“It’s not easy. It definitely takes mindfulness and purpose,” said Cobb. “But the benefits are so great. The feeling of living in line with your core values is something I haven’t truly felt until this period.”

In March of this year, Cobb was named Director of Georgia Tech’s new Global Change Program, a university-wide initiative to provide creative solutions to climate change and other pressing problems, with a heavy focus on engaging students in solutions. She’s taken on the duties of the position with the same determination and mindfulness she has given to the rest of her life. To address climate change, Cobb said, it’s essential that scientists like her put aside their privilege and reach out beyond the ivory tower. 

“We have to inject hope and we need new partners,” said Cobb. “I really like to remind people that in order to move forward, to make progress on something like climate change, we need to bring everybody with us. And when I say, ‘everybody’ I mean everybody.”

As for her fellow scientists, she said the time to act on climate change is now.

“Let’s act as scientists to defend science. Let’s act as scientists to help the public. Let’s be solution makers, not problem identifiers.”