Veterans groups have become a key weapon for environmentalists in their bid to win over swing votes on California Democratic Sen. Barbara Boxer's climate change bill.

But selling the military community on the importance of climate change was not automatic. In fact, five years ago, the topics of climate change and energy efficiency were considered about as relevant to national security as sunspots.

But a combination of battlefield experience sweetened with a few key conversations and a splash of maple syrup helped some retired brass make the connection, and now scores of retired admirals and generals are lending their stars to the boards of energy security organizations in ways that could expand the political base for new climate change policies.

For groups such as VoteVets.org, the message that climate change has huge ramifications for the military is now a mainstay, outstripping even lobbying on the war in Afghanistan.

The group is one of many actively lobbying on the climate bill in the Senate, targeting lawmakers from Arkansas, Montana, Pennsylvania and Florida -- anyone they think needs persuading to vote in favor of Boxer's bill.

"We feel that for so long the national security angle hasn't been expressed, and we're trying to drive that message home," said Jon Soltz, co-founder of VoteVets, who said he expects more paid media messages on the issue. "We're not going to stop. This is just the beginning."

Veterans working on energy security lobbying efforts say a grass-roots group called the Energy Consensus was the catalyst for pulling the ideas and people together.

Jim Woolsey -- who was an undersecretary of the Navy and later the director of the CIA -- provided the initial inspiration, according to Mitzi Wertheim, one of the lead organizers. On the 2004 presidential campaign trail, Wertheim recalled, Woolsey was asked what he'd change if he were president, and he said he'd work to end the nation's dependence on oil from the Middle East.

Marv Langston, another former Navy official, wanted to follow up and asked Wertheim to bring together some people to discuss energy issues. And so the first of many energy talks took place at Wertheim's home near the National Cathedral one snowy evening early in 2005, with just five people.

During the course of that year, Wertheim, a former Peace Corps volunteer and deputy to Woolsey in the Navy, picked up funding from the Pentagon's Office of Force Transformation and hosted more and more of the conversations, pulling together people of all ages from many different fields. Between meetings, they shared articles through e-mail, Wertheim said.

Late in 2005, the group had a major breakthrough when one of its members, Hollywood screenwriter Nora Maccoby, wound up at a holiday party in Georgetown and talked to Defense Secretary Donald Rumsfeld for a half-hour about how the national security strategy should be based on achieving energy independence through renewable clean energy sources.

"I can't believe this -- this girl's kicking my ass, and she's right," The New York Post reported Rumsfeld as commenting on the exchange.

He followed up with one of his famed "snowflake" memos about the importance of the topic, and he invited Maccoby to the Pentagon for a chat.

Maccoby sent an e-mail to the emerging Energy Consensus network: If you had 15 minutes with the defense secretary, what would you tell him?

The ultimate outcome was a big win for the group: a mention of the issue in President George W. Bush's 2006 State of the Union address.

"We have a serious problem: America is addicted to oil, which is often imported from unstable parts of the world," Bush said.

But the group was still encountering high-level resistance from the uniformed military, and the 2006 Quadrennial Defense Review unveiled days later did not include a reference to the energy issue, as the group had hoped.

Efforts at the Pentagon picked up from there, but the next big leap occurred more than a year later, when the Center for Naval Analysis issued a report including testimonials from top retired flag officers.

"We seem to be standing by and, frankly, asking for perfectness in science," Gen. Gordon Sullivan, the former Army chief of staff, said in the report. "But the trend line is very clear." In climate change, he said, "we have a catastrophic event that appears to be inevitable."

As Wertheim and others tell it, Sullivan was skeptical that humans had played a role in causing climate change. So in the run-up to the report, the study group met with people on both sides of the debate. For Sullivan, who grew up in New England, his long-cherished memories of maple syrup, and the impact climate change could have on sugar maples, drove the message home.

Other generals had different triggers, but what it all came back to was the potentially fundamental change that climate change and carbon pollution could bring to the American way of life, said Sherri Goodman, CNA's senior vice president, who shepherded the influential report National Security and the Threat of Climate Change.

After the release of the April 2007 report, then-Sens. John Warner (R-Va.) and Hillary Clinton (D-N.Y.) included a provision in the defense authorization report requiring the Pentagon to consider energy as part of the Quadrennial Defense Review and the National Military Strategy.

Just as important, Goodman said, was the generals' continued support, which she said lends a gravity to the topic beyond the arguments most Americans hear from environmentalists.

But selling the military graybeards on the importance of the issue required hard arguments showing how the military was affected in real ways by climate change, said Rudy DeLeon, senior vice president of national security and international policy at the Center for American Progress.

Citing what many see as weather-related calamities that are striking with increasing fury, possibly because of climate change, DeLeon said that the military services "see the displacement that is occurring when these disasters hit" because of their role in aiding the world's most important humanitarian missions.

On a more basic level, future oil supplies are uncertain; Mexico's reserves could become questionable in the next five to seven years, DeLeon said, and the alternative source is likely to be Africa, where many oil-rich nations are led by dictators. The massive outward flow of America's dollars abroad also threatens the country's security, he said.

Another powerful driver for the military is logistics.

The Pentagon is the biggest customer of fuel in the nation -- and buying it abroad and transporting it added hugely to the price tag -- a reality that hit home last year when oil prices spiked. Bracing against that, the Pentagon is continuing to take on new ventures -- including a pending agreement between the Navy and the Department of Agriculture on developing new biofuels, officials said.