It’s late fall in 2015, and world leaders have gathered in Paris for the United Nations Framework Convention on Climate Change. Under normal circumstances, there would be plenty of tension as representatives from 196 nations try to somehow reach a consensus on how to slow the effects of climate change. But these aren’t normal circumstances. Just a few weeks prior, there was a terrorist attack in Paris and its surrounding suburbs. The attackers killed 130 people and injured nearly 400 more.

Perhaps another time, the conference would have been canceled. But it begins on November 30, as scheduled, because in the opinion of many experts, such as Carnegie Mellon University scientist Neil Donahue, the climate change problem is too dire to delay.

Many of us can simply go outside to understand the urgency of the problem. In the midst of the warmest year on record, sea levels are rising, and ocean temperatures are on the uptick. At the urging of climate scientists spanning the globe, world leaders are under pressure to take action. It’s not easy, though. At the center of this conflict is a mash-up of economics, behavioral change, and politics.

Yet, despite all of the possible obstacles to a consensus, a pact is agreed upon on December 12.

Although not bound to specific carbon-emission limits, the 196 nations agreed to decrease the use of fossil fuels that generate heat-trapping greenhouse-gas emissions such as carbon dioxide as soon as possible. The agreement is meant to prevent average global temperatures from increasing by more than 3.6°F above pre-industrial levels, which, since the 1990s, has been commonly regarded as an adequate target for avoiding irreversible impacts, such as catastrophic sea-level rises and widespread plant and animal extinction.

“This [agreement],” says U.S. President Barack Obama, “sends a powerful signal that the world is fully committed to a low-carbon future. We’ve shown that the world has both the will and the ability to take on this challenge.”

Obama’s perspective is not disputed by Donahue, who is Lord Professor of Chemistry in the departments of chemical engineering, chemistry, engineering and public policy, as well as director of the Steinbrenner Institute for Environmental Education and Research at CMU. But he is far from overjoyed: “I am not comfortable with 3.6F as a magic line where we are safe below it. To the best of our knowledge, the harm from climate change will—more-or-less—get progressively worse, as we have more and more CO2 in the air.

His opinion certainly matters, according to Thomson Reuters, which is considered to be one of the world’s leading news and information sources. The publicly traded company, with more than $12 billion in annual revenues, recently named Donahue among the most cited researchers in the field of geosciences, which addresses critical issues such as energy, meteorology, water and mineral resources, stewardship of the environment, oceanography, and reduction of natural hazards.

For his research, Donahue conducts atmospheric chemistry research focusing on how organic aerosols evolve in the atmosphere. These aerosols are a suspension of particles carried through the air or gas. When they become large enough, they affect how sunlight reflects back into the atmosphere, changing Earth’s climate and energy stores. The result can be visible on especially hazy days or when there is redness in the sunrise or sunset. Don’t be fooled by the picturesque colors, warns Donahue, as they indicate an atmosphere conducive to both air pollution and global warming.

“This [agreement] sends a powerful signal that the world is fully committed to a low-carbon future. We’ve shown that the world has both the will and the ability to take on this challenge.”
U.S. President Barack Obama

“Through air pollution, they kill about 1 million people around the planet every year, and they are a source of huge uncertainty in climate change. It is happening now. It is not just that: ‘Oh, this will affect my grandkids in 100 years.’”

Donahue has become an internationally recognized expert in atmospheric chemistry and air-quality engineering; and his models have helped to improve air-quality standards by predicting the effects of aerosols on the environment if left unchecked.

And his research has found that “left unchecked” is no longer an option: “We are talking about levels of carbon dioxide that we have not seen in at least 55 million years. Just after the dinosaurs was the last time we had carbon dioxide levels like this.”

One of Donahue’s colleagues is equally alarmed:

“Climate change is terrifying to many scientists. We wake up every morning scared to death about what is going to happen in 20 or 30 years,” says Kelly Klima, research scientist, department of engineering and public policy at CMU. Her research focuses on climate change and extreme weather, including impacts on renewable energy, energy continuity, and critical infrastructure. She says Donahue is helping other scientists, industrialists, and policymakers understand the urgency of the situation.

Although many researchers of his stature would be content remaining in the classroom or staying within the confines of the lab, Donahue frequently speaks out about global warming in the media, such as The New York Times, and in the community of atmospheric science and air-quality researchers.

Recently, he has also participated in the 100 Resilient Cities project, which is sponsored by the Rockefeller Foundation and is dedicated to helping cities around the world become more resilient to the physical, social, and economic challenges in the 21st century.

Among the selected cities is Pittsburgh, and its chief resilience officer is Grant Ervin, who says the idea is to tackle environmental issues from sustainability to climate control and create a blueprint for cities and their communities to “survive, grow, and adapt” regardless of conditions—whether it’s a flood, earthquake, or terrorist attack, there needs to be a structural plan in place for the city to withstand these shocks and stresses.

Ervin recruited Donahue because “he has the depth of technical knowledge and practical application that helps us develop a community-based climate action plan. His expertise allows us to ID how policy decisions affect the city at a municipal level. From my point of view, he is a professor for the people. He is accessible.”

Pittsburghers might see the 52-year-old scientist whizzing by on his well-worn road bike throughout the city, heading to the airport for an international summit in Europe, or presenting to local leaders in a stuffy meeting room—but he says what remains consistent is a passion that has driven him since he can remember.

“My father was a space scientist; and, after World War II, he had a bunch of space rockets and sophisticated scientific technology that were used to examine the Earth’s atmosphere. The science part of it was woven into my everyday existence.”

Growing up in Pittsburgh in the 1960s coincided with what many call the birth of the environmental movement through Rachel Carson’s book Silent Spring, which was first published in 1962 and described the harmful effects of pesticides on the environment. Carson grew up just north of Donahue’s hometown.

Silent Spring,” he says, “helped provide for the first time a real sense that through science we had the ability, by eradicating certain fertilizers, to tame nature, spur the green revolution, and feed the planet. In essence, it was optimistic, progressive ideas of what you could do with science and technology to help humanity. An enormous amount of good came out of that, but as we started to look at the planet and study it ... we realized that we can’t tame this thing.”

So it was during that time of social consciousness and the rise of environmental activism when Donahue tapped even deeper into his passion. During his undergraduate days at Brown University from 1981–1985, the physics major joined four other classmates and set up shop on campus:

“Climate change is terrifying to many scientists. We wake up every morning scared to death about what is going to happen in 20 or 30 years.”
Kelly Klima, research scientist

“We built a super-insolated headquarters called the Center for Environmental Studies. It had an apartment in it that was like a living laboratory that five of us lived in. Not exactly self-contained agriculture, but we had greenhouses and gardens. We could monitor our energy use and air quality,” recalls Donahue.

Through this college experience, he began in earnest a journey to what would become his professional life’s work: climate change.

As his work evolves and includes more world travel and talks with policymakers, Donahue says he is increasingly comfortable in his role as one of the “expert” faces of climate change, and he takes the responsibility seriously: “Climate, and more broadly sustainability, is one of the defining issues of the century, and I am doing everything I can to articulate that. Not just sit there and flap my arms and squawk about it, but have meaningful conversations about change.”

In one of the most recent examples, he was among the co-signers of an August 25, 2015, open letter to the Environmental Protection Agency (EPA) and Pennsylvania Governor Tom Wolf, in support of the Clean Power Plan, which the EPA had finalized three weeks prior to the open letter. The plan cuts carbon pollution from existing power plants and offers a comprehensive power plant cleanup package that would reduce air pollution nationwide, including emissions responsible for smog, global warming, acid rain, and mercury contamination. In the letter, Donahue and the co-signers wrote:

Dear Environmental Protection Agency and Governor Wolf,

Your Clean Power Plan to limit carbon pollution from power plants is an essential step forward on the path to reducing carbon pollution and shifting to clean energy. The action couldn’t come soon enough: It is becoming more and more apparent that urgent action on global warming is critical if we are going to secure a safer future for our children. As academics and experts in our fields, we support the EPA and President Obama’s plan to curb global warming pollution. …

We urge you to implement the Clean Power Plan as quickly as possible so we can continue to protect future generations from the worst consequences of global warming and address the largest environmental crisis of our time.

Much like the climate agreement forged in Paris, the Clean Power Plan is not a panacea, says Donahue, but he adds that it is an important step forward: “This is not a story of folks saying we can’t use energy; this is a story of us saying we have to create it differently. Our lives depend on it.”