A former Greely High School student and standout athlete was killed Saturday in Florida while walking barefoot across the country to raise awareness about climate change.

Mark Baumer, 33, was struck by a 2015 Buick SUV while walking along the shoulder of Highway 90 in Walton County, his father, Jim Baumer, said Monday. He was pronounced dead at the scene.

Baumer began walking cross-country barefoot on Oct. 13 to raise awareness about climate change and funds for the FANG Collective, an environmental organization in Providence, Rhode Island.

“I am crossing America barefoot to save earth,” Baumer wrote on his website. “Climate change is the greatest threat we’ve ever faced as a civilization. A lot of scientists agree. I am not a scientist. I am a poet. I am also a regular human being.”

Baumer grew up in Durham, the only son of Jim and Mary Baumer of Brunswick. He was a 2002 graduate of Greely High School in Cumberland and a standout on the school’s baseball team. He was an all-conference power-hitter who earned the respect of players on and off the field.

“Whatever he decided to do, he threw his whole heart into it,” his father said. “He was a tremendous baseball player. He had a great work ethic. He was a great kid.”

Baumer went on to play baseball at Wheaton College in Norton, Massachusetts. During his senior year, the team made it to the Division III National Championship game but fell short. He graduated in 2006, and left the game of baseball.

In July of that year, Baumer began hitchhiking across the U.S. with a friend. They made it to the West Coast in 20 days.

In 2009, he was accepted into the Master of Fine Arts program at Brown University in Providence, Rhode Island. At the end of his first year, he walked across the U.S. in 81 days. He wrote a book about his experience, “I am a Road.”

Baumer returned to Brown University and received his master’s in 2011.

The following year, Baumer took a position at Brown University Library, most recently working as a web content specialist. He took a leave of absence in October to make his second walk across America.

“He was a curious and innovative thinker, who was truly committed to his work at the library and at the university,” said Kerri Hicks, manager of library web services.

While living and working in Providence, he became involved in local labor and social justice causes. He became a union steward and worked to secure a fair contract for librarians at Brown University. He participated in protests against companies such as Providence-based Textron, the last U.S. manufacturer of cluster bombs. He was arrested last year during a protest at Textron.

The arrest didn’t deter him. The experience fueled his passion for activism.

Baumer left again on Oct.13 to walk barefoot across the country. His father said he felt a pull to get back on the road to raise awareness about climate change.

While walking through Ohio, Baumer encountered severe weather conditions and took a Greyhound bus to Jacksonville, Florida. On day 78, he joined a group of activists protesting the Sabal Trail pipeline in the Southeast.

“He was so passionate about the environment and climate change,” his father said. “During the trip, he questioned whether he should be in North Dakota instead of there. Even though he was committed to getting across the country, he wanted to lend his support.”

Baumer documented his trips through various blog posts and videos posted on Facebook and other social media platforms.

“I decided to cross America barefoot to see if I could save earth,” Baumer wrote in a post on a fundraising website. “I know this is a lofty goal, but I hope through my walk I can raise awareness about climate change. If we are ever going to overcome climate change we all need to do everything we can to stop it.”

His goal was to raise $10,000. As of 6:30 p.m. Monday, $18,028 had been raised.

Sonja Siglar of Westville, Florida, was identified as the driver of the SUV that struck and killed Baumer. Police said the driver will face charges, The Associated Press reported.

A celebration of Baumer’s life is tentatively scheduled for Feb. 4 in Providence.