Imagine the unimaginable: some nuclear-armed country (or scary terrorist group) drops a bomb on a perceived enemy. A few million people die, instantaneously or soon. Nuclear winter follows, a period of noontime darkness lasting for decades in which no crops can grow -- and a few billion people starve.

The threat of such a calamity served as table-setting for "The Nuclear Chessboard, 2012," a recent panel discussion sponsored by the Commonwealth Club of California at San Francisco's Mark Hopkins Hotel. The panelists were three of the Americans who best understand how the game is being played.

Former U.S.Senator Sam Nunn and former U.S. Secretary of Defense William Perry, board members of international nonprofit Nuclear Threat Initiative, were joined by former Secretary of State George Shultz for the panel discussion, which was led by former New York Times Washington Bureau chief Philip Taubman, author of The Partnership: Five Cold Warriors and Their Quest to Ban the Bomb. (Nunn, Perry and Shultz are three of the five cold warriors.)

The nuclear chessboard is, of course, no game; and Shultz, Nunn and Perry know this better than most. "We have got to bring nuclear danger back to the forefront," Shultz told the sold-out room. In addition to nuclear-armed countries (and those headed in such a direction,) he said, the fact that terrorists have the technology means it is critical that materials be kept out of the hands of terrorists. "The threat is global."

It would be hard to condense what was an evening of riveting talk (information about future broadcast or transcript is available from Commonwealth Club Media and PR Director Riki Rafner) but a few of the recurring phrases offer keys:

About Iran? Perry spoke of "coercive diplomacy" as the appropriate direction in which affairs should be moving, and Shultz agreed. We might, suggested the latter, say to Iran about their development of materials, "You want to sell on the international market? We'll help you." Thus opening up information about what's there to sell.

"Blending down" is the operative phrase for getting rid of some of the enriched uranium currently existing around the globe. Some countries are beginning to blend down, Nunn said, with encouragement from the Obama administration.

And "warning time" is one of the scary pieces on the chessboard -- but perhaps one of the best hopes. It refers to the amount of time the person in charge has between receipt of information about, say, an imminent attack, and the moment he pulls the nuclear trigger. Perry responded to an audience question about close calls that came during his time as Secretary of Defense by saying that there had indeed been a few false alarms. One call in the middle of the night reported that a computer screen was showing 200 missiles headed in our direction. Fortunately, the general making the call was already doubting the computer, and Perry ultimately did not make the call to the White House narrowing the warning-time window. Nunn said progress is being made on extending the warning time, "But we need to go from minutes to hours to days..."

The cold warriors were guardedly optimistic about progress in reduction of nuclear weapons. Quoting former Secretary of Defense Robert Macnamara's assessment that 100 nuclear weapons are sufficient for deterrent and questioning why the U.S. needs to have thousands, Perry said, "We want to go down arm in arm with the Russians, and we have got to make sure other countries come down at the same time."

All of which still sounds a little like the game this whole global mess decidedly is not. "There must be," said Shultz, "interaction between the vision of a world free of nuclear weapons and the steps you have to take to achieve that vision."

A first step: public awareness and information. Audience members who asked how to take that first step were directed to the home address of the cold warriors at Nuclear Threat Initiative. NTI's logo proclaims its mission for building a safer world. One can hope.