What's the big deal with the number 350? To Bill McKibben, an environmental activist and bestselling author, and anyone involved with the 350 organization, it means the world.

Scientifically, 350 represents the "red line" for the amount of carbon dioxide (in parts per million) in the atmosphere before there is irreversible damage done to Earth. The current level is 387 parts per million and rising.

Mckibben's lecture, "The Most Important Number in the World: Building a Worldwide Movement to Fight Climate Change," was given in Sauder Concert Hall on Wednesday and was the annual Yoder Public Affairs Lecture.

McKibben encouraged the Goshen community to take part in "A Global Day of Climate Change" on Oct. 24, which the 350 organization is sponsoring. The goal of the movement is to raise global awareness about the importance of the number 350. "We tried to imagine how we can move the world all at once," said McKibben.

There will be people doing creative projects to get people aware of the number. Some will climb the Himalayas holding signs, and others will hold signs underwater in the coral reefs. Goshen might not have mountains or oceans, but McKibben looks forward to seeing what creative ideas Goshen comes up with to spread the word.

"I'm gonna wait with great anticipation to see what Goshen does," McKibben said.

The idea is to use the number as a slogan for the movement rather than using words. According to McKibben, "It sets a real limit. It forces people to say this plan does or does not get us back to where we need to be. It's a problem we have to solve very very quickly."

According to McKibben, before the industrial revolution, the amount of carbon in the air was fairly stable at around 270 parts per million. That number began to rise, and it was thought the "red line" number was close to 500, which would give us more time to adjust. As research continued, the number lowered significantly to 350 parts per million.

McKibben also believes the number is helpful because it can be understood around the world, and spreading the message around the world is one way McKibben thinks Goshen can help the cause.

"I don't only want you to organize something for October 24," McKibben said. "The real reason I wanted to come here today is because I know this community has tremendous links all around the world ... you have just what we need, links to who can hear and help with this message."

McKibben believes the message about the environmental crisis moves beyond political agendas. "We need to go way beyond the usual, political, ideology," McKibben said. "It's a very radical proposition to say let's keep pouring carbon into the atmosphere and see what happens."

McKibben is no beginner when it comes to political action. In 2006 he led a five day walk across Vermont to persuade political leaders in the state to commit to cutting carbon emissions 80 percent by 2050. The action worked, and political leaders from both parties signed the pledge.

In 2007, McKibben helped start Stepitup.org, which organized more than 1,400 demonstrations across all 50 states. Three days later, Barack Obama and Hillary Clinton changed their platforms on climate change.

McKibben is the author of numerous books about global warming, alternative energy and the risks associated with human genetic engineering. His latest book, “Deep Economy” (Times Books, 2007), was a national bestseller.

McKibben is also a frequent contributor to various magazines including The New York Times, The Atlantic Monthly, Harper's, Orion Magazine, Mother Jones, The New York Review of Books, Granta, Rolling Stone and Outside.

The Yoder Public Affairs Lecture Series began in 1978 when Frank and Betty Jo Yoder of Goshen created an endowed lectureship to enable faculty, students and community members to hear widely known speakers address current issues.

"I can't promise you that this is gonna work," McKibben said. "It's kind of like throwing a hail mary pass at the end of a football game."

Download a podcast of Bill McKibben's speech below:

McKibben speech

Download a podcast of the question and answer session with Bill McKibben below:

McKibben Q&A