Add to that flights to Paris, Rome, Vancouver and elsewhere. All told, in the last three years, she's flown 29 times to study, meet or talk about global warming.

Then Cobb thought about how much her personal actions were contributing to the climate crisis, so she created a spreadsheet. She found that those flights added more than 73,000 pounds of heat-trapping carbon to the air.

Now she is about to ground herself, and she is not alone. Some climate scientists and activists are limiting their flying, their consumption of meat and their overall carbon footprints to avoid adding to the global warming they study. Cobb will fly just once next year, to attend a massive international science meeting in Chile.

"People want to be part of the solution," she said. "Especially when they spent their whole lives with their noses stuck up against" data showing the problem.

The issue divides climate scientists and activists and plays out on social media. Texas Tech's Katharine Hayhoe, an atmospheric scientist who flies once a month, often to talk to climate doubters in the evangelical Christian movement, was blasted on Twitter because she keeps flying.

Hayhoe and other still-flying scientists note that aviation is only 3% of global carbon emissions.

Jonathan Foley, executive director of the climate solutions think-tank Project Drawdown, limits his airline trips but will not stop flying because, he says, he must meet with donors to keep his organization alive. He calls flight shaming "the climate movement eating its own."

Over the next couple of weeks, climate scientists and environmental advocates will fly across the globe. Some will be jetting to Madrid for United Nations climate negotiations. Others, including Cobb, will fly to San Francisco for a major earth sciences conference, her last for a while.

"I feel real torn about that," said Indiana University's Shahzeen Attari, who studies human behavior and climate change. She calls Cobb an important climate communicator. "I don't want to clip her wings."

But Cobb and Hayhoe are judged by their audiences on how much energy they use themselves, Attari said.

Attari's research shows that audiences are turned off by scientists who use lots of energy at home. Listeners are more likely to respond to experts who use less electricity.

"It's like having an overweight doctor giving you dieting advice," Attari said. She found that scientists who fly to give talks bother people less.

In science, flying is "deeply embedded in how we do academic work," said Steven Allen, a management researcher at the University of Sheffield, who recently organized a symposium aimed at reducing flying in academia. He said the conference went well, with 60 people participating remotely from 12 countries.

Pennsylvania State University's Michael Mann, who flies but less than he used to, said moderation is key.

"I don't tell people they need to become childless, off-the-grid hermits. And I'm not one myself," Mann said in an email. "I do tell people that individual action is PART of the solution, and that there are many things we can do in our everyday lives that save us money, make us healthier, make us feel better about ourselves AND decrease our environmental footprint. Why wouldn't we do those things?"

Mann said he gets his electricity from renewables, drives a hybrid vehicle, doesn't eat meat and has one child.

When Hayhoe flies, she makes sure to bundle in several lectures and visits into one flight, including 30 talks in Alaska in one five-day trip. She said more people come out to see a lecture than if it were given remotely, and she also learns from talking to the people at lectures.

"They need a catalyst to get to the next step and me coming could be that catalyst," Hayhoe said.

Marshall Shepherd of the University of Georgia will receive a climate communications award at the American Geophysical Union conference Wednesday in San Francisco. But he won't pick it up in person, saving 1.2 tons of carbon by not flying. He said he doesn't judge those who fly but wrote about his decision to stay grounded in hopes that people "think about choices and all of the nuances involved in these decisions."

Former Vice President Al Gore, who has long been criticized by those who reject climate science for his personal energy use, said he has installed 1,000 solar panels at his farm, eats a vegan diet and drives an electric vehicle.

"As important as it to change lightbulbs," he said in an email, "it is far more important to change the policies and laws in the nation and places where we live."

Teen activist Greta Thunberg drew attention when she took a zero-carbon sailboat across the Atlantic instead of flying.

"I'm not telling anyone else what to do or what not to do," Thunberg told The Associated Press before her return boat trip. "I want to put focus on the fact that you basically can't live sustainable today. It's practically impossible."

Cobb is trying. In 2017, she started biking to work instead of driving. She's installed solar panels, dries clothes on a line, composts and gave up meat. All these made her feel better, physically and mentally, and gave her more hope that people can do enough to curb the worst of climate change.

But when she did the math, she found "all of this stuff is very small compared to flying."

Cobb began turning down flights and offering to talk remotely. This year she passed on 11 flights, including Paris, Beijing and Sydney.

"There hasn't been a single step I have taken that has not brought me a deeper appreciation for what we're up against and what's possible," Cobb said. "This gave me a profound appreciation for how individual action connects to collective action."

But there's a cost.

Cobb was invited to be the plenary speaker wrapping up a major ocean sciences conference next year in San Diego. It's a plum role. Cobb asked organizers if she could do it remotely. They said no. She promised to do many roles for the conference from Atlanta. Conference organizers withdrew the offer.

Brooks Hanson, executive vice president of the American Geophysical Union, which runs the conference, said in an email that the group supports remote presentations whenever possible. But the wrap-up speaker position "requires in-person interactions with attendees to get the vibe of the meeting and discussions," Hanson said.

Foley said that shows the problem: "Climate scientists and activists should walk the walk. But we can only walk so far. Then you bump into other things."