A group of activists is taking a different angle to argue for cap and trade: national security.

As part of a bus tour through 16 states, Operation Free will hold town halls and campus meetings and interview with local media to argue that climate change is a threat to national security.

Their arguments: Extremists thrive in areas where rising sea levels and natural disasters have caused food and water shortages. Foreign oil dollars can fall in the hands of terrorist groups, while humanitarian relief missions stretch an already taxed military.

"People like me have seen first hand the effects of our energy policy," said Jonathan Gensler, who served during the first year of the current Iraq war. He participated in two Operation Free bus tours last fall through his home state of West Virginia.

At the local meetings, Gensler tries to use his credibility as a veteran to sway people to care about climate change.

"I've buried a number of friends …. A couple of them died from car bombs that were funded in some part by American dollars being sent to foreign oil dictators," he said.

Hundreds of veterans like Gensler have participated since the buses took off last summer. The group is currently on its third and biggest tour, which kicked off in Washington, D.C., last week.

After 11 stops in Virginia and Missouri, the bus will make its way through Colorado. By the end of February, they plan to get through Arizona, Washington, North Dakota and Ohio.

The project is supported by the Truman National Security Project, an advocacy group started by veterans who supported Sen. John Kerry (D-Mass.) during his 2004 presidential run. The group has since committed itself to one of Kerry’s biggest priorities: passing a climate bill.

"The threat climate change is causing in places like sub-Saharan Africa is a destabilizing force," said Jonathan Powers, also an Iraq vet and chief operating officer of the Truman Project. "It creates migration, fragile governments. That's exactly the type of breeding ground where we have to go and fight."

The Pentagon is expected to echo that argument in a Quadrennial Defense Review due out Monday. Congress requires the study every four years to help the military chart its way forward.