Switching to lower-energy-use CFL lightbulbs and driving a hybrid car are good responses to the planet's climate crisis, says Lester Brown, the internationally recognized climate-change advocate, but the most important step a concerned citizen can take is to become politically active, he told a near capacity crowd at Cary Hall in Lexington Sunday night.

"Saving civilization is not a spectator sport," he said near the end of his hour-plus address, using the sort of sweeping language that characterized his remarks.

Though his speech was peppered with statistics that both sketched the fathomable boundaries of the problem and made solutions seem no further than the flip of a billion switches, his bottom-line prescription was a change in tax policy that would lower income taxes and raise property taxes and spur investments in energy efficiency and renewable power generation.

He said such an approach is favored by economists, while a cap-and-trade system in which energy-saving steps have financial value that can be swapped by corporations, is favored by government and industry. The three leading presidential candidates all have cap-and-trade proposals.

In questioning from the floor after his remarks, Brown spoke favorably about Barack Obama, not for his policies but for "his ability to motivate people to get involved. We need people who are more than good technicians. So if I were to pick someone who has the potential to do this, it would be him," Brown said.

The founder of Worldwatch and the Earth Policy Institute, two institutions that have looked at global issues over more than 30 years, Brown began by sketching the problem, focusing first on the increasing incidents of large scale ice melts of glaciers in Greenland and in Asia. Complete loss in Greenland would provoke huge rises in sea levels, while in Asia, he said, the glaciers feed the rivers that irrigate the most productive wheat and rice fields in the world, and their loss would trigger "changes we can hardly begin to grasp."

He also said the world has a growing roster of failing states, which he said can begin to be seen as evidence of a failing civilization. As forests collapse and deserts expand, he said, it becomes more difficult for governments to respond.

And now, he said, there are two new stress points:

* Peak oil, which describes the zenith of petroleum output worldwide. Up to now, he said, expanding output has allowed unfettered access, but once production can no longer expand, "no country gets more oil unless another gets less." He said some analysts say production has already peaked, while many others say it is fast approaching.

* The merging of the food and energy economies. By the end of the year, he said, about 30 percent of grain in this country will go to making ethanol, and the rising competition for that grain has raised food prices to historically high levels. He said the effect of such a merger will be to pit the 860 million drivers in the world who want to motor on that grain against the 2 billion poorest people who want to eat it, leading to political instability.

Brown said the increasing magnitude of climate change has made obsolete the previous goal of cutting carbon emissions 80 percent by 2050. "We need to do it by 2020. It's like a wartime mobilization," he said. Brown identified three fronts in his call to arms: increased energy efficiency, "a massive shift to renewables," and a campaign to plant hundreds of billions of trees.

"This is our new defense budget," he said. "The real threats to our safety are not powerful states but the powerful forces of poverty, climate change, and population growth, and weapons technology won't help us with those."

Saying that we are in "a race of tipping points," he acknowledged that many people wonder if needed changes can be made in time, but drew an optimistic comparison to events at the beginning of World War II. Just a month after the attack on Pearl Harbor, he said, President Franklin Roosevelt set out very ambitious military procurement goals in his State of the Union address.

Though there was a lot of skepticism that goals could be met, they were in many cases exceeded by a refocusing of the nation's industrial output, "not in decades or years, but in months. We could do that again," he said.

"Today the stakes are higher," he said. "It's not just a way of life. It's the future of civilization that's at stake."

The event was hosted the Lexington Global Warming Action Coalition, and attended by a fairly homogeneous crowd of older Caucasians who well played the role of the converted to Brown's preaching, which he acknowledged. Afterward, a line snaked through the hall's antechamber as audience members sought to meet Brown and have him sign their copies of Brown's latest book, "Plan B 3.0, Mobilizing to Save Civilization."

A sizable minority were members of the Union of Concerned Scientists, whose president, Kevin Knobloch, introduced Brown. As a brief warm-up to the main event, Congressman Ed Markey, chairman of the House Select Committee on Energy Independence and Global Warming, spoke about his accomplishments and posited his three-focus approach to climate rescue: energy efficiency, renewable energy, and shutting down coal-fired electrical plants.