UNITY — The largest senior class in Unity College’s 43-year history was urged to “direct your devotion to the natural world onto a path toward its stewardship” during commencement exercises held Saturday.

Keynote speaker Cynthia Barnett, described by The Boston Globe as “part journalist, part mom, part historian and part optimist,” is the author of two books on what she terms a “water ethic for America.” She’s been an active journalist for more than 25 years and has won a Sigma Delta Chi award for investigative journalism and eight Green Eyeshade awards, which recognize outstanding journalism in 11 southeastern states.

Unity College and its 146 members of the class of 2012 seemed to be a perfect match for Barnett, who praised the decision of the students “for having that early wisdom to direct your devotion to the natural world onto a path toward its stewardship.”

Barnett cautioned the graduates that they’ll be leaving “this bucolic corner of Maine to find a nation and a world paralyzed by an inability to work together on the greatest challenge our species has ever faced. As the global atmosphere warms, as the Arctic ice thins, as Americans sweat out the warmest spring in recorded history, our political, cultural and business leaders — and our government and private institutions — remain frozen stiff.”

Still, the author was optimistic about the influence of the “caring middle” who embrace neither the conservative or liberal side of environmental issues. “The initial impacts of our changing climate all involve water — altered rainfall and storm patterns, more extreme flooring, more severe droughts. … This is why I’ve come to believe water will be the issue around which the shouting match over climate change finally becomes a conversation.”

Still, the author was optimistic about the influence of the “caring middle” who embrace neither the conservative or liberal side of environmental issues. “The initial impacts of our changing climate all involve water — altered rainfall and storm patterns, more extreme flooring, more severe droughts. … This is why I’ve come to believe water will be the issue around which the shouting match over climate change finally becomes a conversation.”

The Unity College commencement was also the first for Dr. Stephen Mulkey, who was inaugurated earlier in the day. Mulkey, the college’s 10th president, previously was director of the environmental science program at the University of Idaho and worked for many yeas as a research associate for the Smithsonian Institution’s Tropical Research Institute.

“Since coming to Unity College in July, I have come to realize that the student culture is far more inclusive and mutually supporting than any other student culture in my experience,” Mulkey said. “You, the class of 2012, should be deeply proud of this.”

The president added that Unity College “is a place where everyone knows your name, and you are part of a community. It is community that makes us resilient, that makes us ‘the little college that could,’ and did. We were environmental before environmental was cool. We embraced sustainability before sustainability was cool.”

Amy Kennedy, the recipient of the Faculty Award, also was selected to give the student address.

“The staff and faculty at Unity (College) have done way more than provide us with an environment to learn in. They have helped shape us into the people we are now and have helped to prepare us for the world we are about to join,” Kennedy said.

An honorary doctorate of arts and humanities was conferred on Lewis Turco, professor emeritus of English writing and arts at SUNY College, Oswego, N.Y. He is best known as the author of “Book of Forms: A Handbook of Poetics,” commonly called “the poet’s bible.”

Turco’s daughter, Melora Norman, was the co-presenter of the award with family friend Michelle Leavitt.