Childhood questions became lifelong quests

Dinosaurs’ demise, Martian environment and Earth’s climate fascinated Brian Toon as a kid, captivated him as a scientist, and propelled him to a wide-ranging research career marked by a common theme: tiny airborne particles

Since he was a kid, Owen Brian Toon has puzzled over “weird problems”: What killed the dinosaurs? What’s Mars like? What causes Earth’s climate to change?

Early on, he had another question: Is there really a Yeti? “When I was 10 years old, that was a big problem,” says Toon, now a professor of atmospheric and oceanic sciences at the University of Colorado.

The alleged Yeti, or “abominable snowman,” was debunked decades ago. “This is a problem solved everywhere, except on television programs shown regularly to our children and falsely advertized as science or history.”

But Toon has spent much of his professional life studying—and broadening knowledge of—the other three problems. His years of research on these topics have earned him the 2011 Roger Revelle Medal from the American Geophysical Union.

That distinction is bestowed on one person a year by the 60,000-member organization “for outstanding contributions in atmospheric sciences, atmosphere-ocean coupling, atmosphere-land coupling, biogeochemical cycles, climate or related aspects of the Earth system.”

By studying Mars and Venus, Toon and other scientists gained greater insight into the climate of the Earth. The greenhouse effect—that gases such as carbon dioxide trap heat in a planet’s atmosphere—has been known for more than a century. But manmade greenhouse gases aren’t the whole story, Toon notes.

Venus, which has atmospheric CO₂ concentrations 100,000 times higher than that of Earth, is “hotter than a self-cleaning oven,” Toon observes. But while Mars’ atmospheric CO₂ concentration is about 20 times higher than Earth’s, Mars is colder than Antarctica.

“It isn’t just the distant location of Mars from the sun that makes it cold, either,” says Toon, because Venus uses little more sunlight than Mars does. “Rather, it is the way that water vapor and carbon dioxide have evolved over geologic history.  It is low water vapor that makes Mars so cold today. Possibly giant impacts warmed Mars in the distant past by injecting lots of water into the Martian atmosphere.”

Aerosols are implicated in the demise of the dinosaurs, which are thought to have been wiped out by the effects of a gigantic asteroid that slammed into Earth 65 million years ago. “I was thinking, how could asteroids kill dinosaurs? … You have these microscopic particles killing the largest carnivores on the planet.”

Toon and others suggest that searing heat from the re-entry of the impact debris “basically broiled the dinosaurs alive.” Widespread fires then released a thick blanket of soot that blocked sunlight, cooled the planet and halted photosynthesis. Mass extinction followed.

Studying the effects of an asteroid impact led Toon and others to the study of the worldwide effects of nuclear war: That work concluded that most of the world’s humans would be killed by widespread nuclear war.

Toon is a top authority on the aftermath of nuclear war. The term “nuclear winter” stems from a landmark paper published in Science in 1983 and written by R.P. Turco, Toon, T.P. Ackerman, as well as the late J.B. Pollack  and Carl Sagan.

“Nuclear winter” denotes a worldwide drop in temperatures due to the dust and soot from firestorms that would block sunlight after nuclear war.

The 1983 nuclear-winter study assumed a war involving 5,000 megatons of explosions—about 2,500 times the explosive power of all the bombs detonated in World War II.

In recent years, Toon has led or contributed to several studies showing that even a “limited nuclear war”—involving an iota of the firepower studied previously—would devastate the stratospheric ozone layer and plunge the world into devastating frigidity. Global average temperatures would be colder than any seen in the last thousand years.

In 2006, Toon helped lead two studies that found that even a small-scale nuclear war—one involving 100 15-kiloton explosions—could slaughter as many people as were killed during World War II and disrupt the world’s climate (and food production) for a decade.

Toon noted that nations such as Pakistan and India have the capacity to detonate 50 nuclear bombs, each having 15 kilotons of explosive power—the power of the nuclear bomb dropped on Hiroshima.

In 2007, Toon, Rich Turco of UCLA, Alan Robock of Rutgers University and others published a paper in Science emphasizing the devastation that could follow a “limited,” or regional, nuclear war involving 100 15-kiloton bombs. Such a war would involve a trivial portion of the world’s nuclear arsenal: less than one-tenth of 1 percent of the world’s nukes.

Besides the immediate casualties, Toon and his colleagues found, such a war would cause massive fires that could propel 1 million to 5 million tons of soot into the high atmosphere.

World political leaders aren’t paying sufficient attention to nuclear proliferation, Toon says. “They think that if India and Pakistan had a war, ‘That won’t affect us.’”

Toon and Robock summarized this work in a Scientific American article published last year. They made a forceful case for disarmament: “Rapid reduction of the American and Russian arsenals would set an example for the rest of the world that nuclear weapons cannot be used and are not needed.”

Toon’s research has also helped explain another global threat: the destruction of stratospheric ozone over Antarctica. He correctly predicted that polar stratospheric clouds containing nitric and hydrochloric acid form in the Antarctic stratosphere in winter. He also predicted that the polar stratospheric clouds would catalyze chemical reactions that produce reactive chlorine, which destroys stratospheric ozone.

“Susan Solomon suggested some ozone-destroying reactions that might occur. I showed why they would occur. Maggie Tolbert and Mario Molina showed they did occur in the lab, and I helped lead aircraft expeditions that showed they did occur in nature.”

“There’s a theme here of particles,” Toon observes, noting that this theme underlies much of his research.

As Toon notes, aerosols are of many types and exhibit more complex behaviors than do greenhouse gases.

“CO₂, once you say its name and measure it in one place, you know almost everything you need to know about it,” Toon says. About 20 percent of the carbon dioxide you emit driving home today will linger in the atmosphere thousands of years. The slow rate of change makes CO₂ easier to understand.

But aerosols emitted in the last week are offsetting the climate effects of much of the greenhouse gases so far emitted, Toon adds.

Further, aerosols can have cooling or warming effects. Aerosols interact with about 10 percent of all the Sun’s energy, reflecting much of that back into space. Most particles, dust or sea salt or sulfates, can scatter sunlight, blunting the warming effect of sunlight.

Dark particles, such as diesel soot or forest-fire smoke, can absorb sunlight and have a warming effect, or they can fall on snow, reducing surface reflectivity and making snow melt faster.

Aerosols can also be deadly. About 30,000 Americans die each year from ailments traced to airborne particulates. Coal-fired power plants are a major source of this morbidity.

While there’s much left to learn, Toon notes “a growing anti-science movement” in America. In public-opinion surveys, more than 40 percent of the U.S. population reported believing the Earth is about 6,000 years old (rather than its actual age of 4.5 billion years).

Toon asks: “What does this say about science education? What does this say about our ability to communicate the facts of science?”

Noting that there is a “huge science-education problem in the United States,” Toon says the solution is not straightforward. “It’s not just information transfer. It’s resistance to knowing the information, and confusion produced by the entertainment industry and others often in the name of science or news.”

There’s also a view that facts are open to interpretation. “Facts are not open to interpretation. Facts are facts.”

Toon earned his Ph.D. in physics from Cornell University in 1975 with Professor Carl Sagan. He became a NASA research scientist in 1978 and joined the CU faculty in 1997. He has been elected a fellow of the American Geophysical Union and the American Meteorological Association. He is recognized by ISI Thompson Scientific as one of the most highly cited and influential geosciences researchers.

Additionally, he was recognized by the United Nations’ Intergovernmental Panel on Climate Change for significant contributions to the body of work honored by the 2007 Nobel Peace Prize.

As for the Roger Revelle Medal, which he will receive in San Francisco in December, Toon notes, “It’s nice to have your colleagues say you’ve done some interesting things.”

“This award recognizes students and post-docs and all my collaborators,” he adds. “I’m having a fun time exploring all these topics, and they’re doing all the work.”

Plus, “I’m still working on the same problems that I was trying to understand when I was 10.”

Except, of course, the Yeti.