Kristen's Web site, "Ponder the Maunder," has made her a celebrity among climate skeptics. After she posted a critique of Al Gore's movie An Inconvenient Truth, her Web site got so many hits the family's internet service provider sent them a warning.
Her story may dismay mainstream scientists, but plenty of people are friendly to her ideas.
In one poll last year, only about 50 percent of people agreed humans were contributing to global warming. The other half either disagreed, weren't sure or didn't believe the Earth was warming in the first place.
"I don't remember how old I was when I started getting into global warming," Kristen says. "In middle school I remember everyone was like: 'Global warming! The world is going to end!' Stuff like that ... so I never really believed in it."
On the March afternoon I visited, there was still snow on the ground in Maine, and Kristen padded around the house wearing green furry slippers. She earns top grades in school. (Her step-dad, Mike Carson, proudly shows them off.)
And she has a quality scientists try to cultivate: she is skeptical. Has someone made a claim? She wants to see the data.
So about a year ago, when she was 15, she started to look at the scientific evidence. When she got confused, she consulted Mike.
Soon they had printed out a mound of technical documents from the Internet.
Kristen was convinced by the skeptics and she began to write, summarizing their arguments adding her own touches. Yes, she says, the Earth is warming. But no, humans aren't causing it. She says it's part of the natural climate cycle.
At some point, Mike and Kristen decided to post her work online.
"I felt it was important to inform people that this wasn't completely true," Kristen says. "A public service to let people know."
Mike set up the Web site and Kristen's mom, Tammy Byrnes, typed. Soon "Ponder the Maunder" was born. Kristen admits the title is a little obscure. It's a reference to a dip in solar activity in the 1600s known as the "Maunder minimum."
Her Web site includes charts of temperature records, El Nino indexes, isotope measurements. Skeptics loved it: A 15-year-old attacking the mainstream scientific view.
"It took off like wildfire," Mike says, "But that was nothing compared to when her Al Gore critique went up."
Kristen had no fear. She took on Al Gore the Nobel laureate, Academy Award winner and former vice president. She went after Jim Hansen, one of NASA's top climate scientists. E-mail poured in, mostly from skeptics happy a young person had taken up the cause.
"I got a letter in the mail on my birthday from a senator," she says.
Someone runs off into another room to track it down and returns with an envelope from the office of Sen. James Inhofe, the Oklahoma Republican famous for calling global warming a hoax.
"Dear Kristen," the letter begins. "Thank you so much for your letter and e-mail and for your kind words. I appreciate your help in the fight against global warming alarmism. You are a common sense young lady and an inspiration to me. I want you to keep up the good work. We are winning."
Mainstream scientists would argue that many of the issues on her Web site are red herrings or have been put to rest — and Kristen did get emails from people challenging her science. But after a few exchanges, she says, her opponents backed down. "A few of them gave up and figured they can't win against a 15-year-old," she says. Mike laughs as she says this.
Kristen says when her determination sagged, Mike encouraged her.
"Kristen! MOTIVATION!" she remembers him saying. Mike is deeply skeptical humans are behind global warming and pulls up a graph on the computer to help make the case.
And the truth is, for people who want to get down into the details, climate change science can get very hairy. There are oceans to consider, which can absorb heat, water vapor and cloud cover to account for.
Much of the evidence comes from detailed computer models. Scientists disagree on some of the details. A handful do not think the case has been made. But the overwhelming consensus is that humans are causing global warming, and the consequences could be serious.
Despite Kristen's online celebrity, she doesn't talk about climate change much with her friends.
During lunch at a local chowder house with her friend Chrissy Flanders, they talked about food and friends and clothes.
So it came as somewhat of a surprise when Chrissy piped up to say she disagreed with Kristen on climate change.
"I think it's partly because of humans," she says. Asked why she believes that she says she doesn't know. Kristen chimes in: "She just believes what everyone else is making her believe."
It's probably fair to say that most people — even those who have strong opinions about global warming — couldn't make a strong scientific argument for why they believe what they believe.
Most of us delegate, decide to believe someone we trust. We don't actively seek out the other side. We probably wouldn't know what to make of it, or how to reconcile the two. Who has time? Or the expertise?
Kristen is getting out of the climate-change business. She thinks she would like to become an architect — maybe even build energy-efficient "green" buildings.
She does not see herself as an environmentalist, though. She says that makes her think of hippies.
The truth is easy to see when you educate yourself on the facts, rather than blindly follow others like Kristen's friend; who says "she doesn't know" why she believes what she believes.