Tuesday, December 06, 2022

Wally Broker predicted how the climate could suddenly change

In the mid-1980s, at a meeting in Switzerland, Wally Broker’s ears perked up. Scientist Hans Oshgar was describing an ice core drilled at a military radar station in southern Greenland. Layer by layer, the 2-km-long core revealed what the climate was like thousands of years ago. Climate change, predictable by the amount of carbon dioxide and oxygen in the core, played out surprisingly quickly – within just a few decades. It almost seemed too fast to be true.

Broker returned home to Columbia University’s Lamont-Doherty Earth Observatory, and began to wonder what might have caused such a dramatic change. Some of Oeschger’s data turned out to be wrong, but the seed they sowed in Brocker’s mind has blossomed — and ultimately changed the way scientists think about climates of the past and future.

Broker, a geochemist who studies the oceans, proposed that the closure of a major ocean circulation pattern, which he named the Great Ocean Conveyor, could have abruptly changed the North Atlantic climate. In the past, he argued, melting ice sheets have sent huge pulses of water into the North Atlantic, making the water fresher and preventing circulation patterns that rely on salty water. The result: a sudden atmospheric cooling that plunged the region, including Greenland, into a great cold. (in the 2004 film personA highly dramatic sea shutdown coats the Statue of Liberty in ice.)

It was a leap of insight unprecedented for a time when most researchers hadn’t yet recognized that the climate could change abruptly, with little consideration of what might have caused such changes.

Brocker not only explained the observed changes in Greenland’s ice core, but he also discovered a new area. He enlisted, coaxed, and brought together other scientists to study the entire climate system and how it may have changed all at once. “He was a really big thinker,” says Dorothy Petit, a paleontologist at NASA’s Goddard Institute for Space Studies in New York City, who worked with Broker for decades. “It was his genuine curiosity about how the world works.”

Broker was born in 1931 to a fundamentalist family who believed the Earth to be 6,000 years old, so he was not an obvious candidate to be a pioneering geologist. Because of his dyslexia, he relied on conversation and visual aids to absorb information. Throughout his life, he did not use a computer, which is a fixture of modern science, yet he became an expert in radiocarbon dating. And, unlike the common siloing in science, he worked extensively to understand the oceans, atmosphere, land, and thus the entire Earth system.

By the 1970s, scientists knew that humans were adding extra carbon dioxide to the atmosphere through burning fossil fuels and cutting down carbon-storing forests, and that those changes were tinkering with Earth’s natural thermostat. Scientists knew that the climate had changed in the past; Geologic evidence spanning billions of years suggests warm or dry, cold or wet periods. But many scientists focused on long-term climate changes, the way the Earth spins on its axis and orbits the Sun—both of which change the amount of sunlight the planet receives. A highly influential 1976 paper referred to these orbital shifts as “the pacemakers of the Ice Age”.

The ice cores of Antarctica and Greenland changed the game. In 1969, Willi Dansgaard of the University of Copenhagen and his colleagues reported the results of a Greenland ice core covering the last 100,000 years. They found large, rapid fluctuations in oxygen-18, suggesting wild temperature fluctuations. The climate could have oscillated faster, it seemed – but it took another Greenland ice core and it was more than a decade before Brock had the idea that the shutdown of the Great Ocean Conveyor System might be to blame.

Photo Of An Ice Core Drilling Set-Up By Drill With One Scientist And Another Scientist In The Background
The Die-3 ice core (the drill used to retrieve the core is shown) pulled from southern Greenland beginning in 1979 showed that there had been abrupt climate change in the past.Niels Bohr Institute

The broker proposed that such a shutdown was attributable to a known cold snap that began about 12,900 years ago. As Earth began to emerge from its orbital impacted ice age, water melted from the northern ice sheets and washed away in the North Atlantic. He said that the movement of the sea stopped, causing Europe to suddenly freeze. The period, lasting more than a millennium, is known as the Younger Dryas after the Arctic flower that flourished during cold snaps. It was the last hurricane of the last ice age.

Evidence that an ocean conveyor shutdown could cause dramatic climate change soon piled up in Broker’s favor. For example, Petit found evidence of rapid cooling of smaller Dryas in swamps near New York City—thus establishing that the cooling was not just a European phenomenon, but also extended to the other side of the Atlantic. The changes were real, widespread and swift.

In the late 1980s and early ’90s, there was enough evidence supporting sudden climate change that two major projects – one European, one American – began to drill a pair of fresh cores into the Greenland ice sheet. done. Richard Alley, a geologist at Penn State, remembers working through the layers and documenting small climate changes over thousands of years. “Then we hit the end of the Younger Drys and it was like falling off a cliff,” he says. “It was a big change after many small changes,” he says. “Beautiful.”

The new Greenland core solidifies scientific validation of sudden climate change. Although the closure of the ocean carrier cannot explain all the sudden climate changes that ever occurred, it did show how a single physical system could trigger major planet-wide disruptions. It also discussed how rapidly the climate could change in the future.

Brocker, who died in 2019, spent his last decades exploring the abrupt changes taking place from earlier. For example, he worked with billionaire Gary Comer, who was shocked by shrinking Arctic sea ice during a boat trip in 2001, to brainstorm new directions for climate research and climate solutions.

The broker knew more than almost anyone what could happen. He often described the Earth’s climate system as an angry beast that humans are killing with sticks. And one of his most famous papers was titled “Climate Change: Are We on the Verge of a Clear Global Warming?”

It was published in 1975.

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