The annual commemorations of the U.S. atomic bombings of Hiroshima and Nagasaki are solemn reminders that for the last 64 years humanity has existed on the brink of a precipice ― the threat that life as we know it could be snuffed out if the terrible power of the world’s nuclear arsenals were ever unleashed.

In remarks to the World Federation of United Nations Associations meeting in Seoul, South Korea this week, UN Secretary General Ban Ki-moon highlighted both the urgency and the possibility of nuclear disarmament.

Noting that with the ongoing talks between the U.S. and Russia, “for the first time in a decade, negotiators have agreed to a package of measures that can move the world away from nuclear weapons,” he added, “Now is our time … time to build on this momentum.”

And indeed, momentum IS building around the world. In June the U.S. Conference of Mayors unanimously passed a resolution affirming cities’ role in ending nuclear weapons by 2020. “As long as nuclear weapons exist,” the resolution warns, “cities around the world will be vulnerable to instantaneous devastation on a scale exceeding even that experienced by Hiroshima and Nagasaki in 1945.”

The International Trade Union Confederation and the worldwide Mayors for Peace have launched an international campaign leading up to next May’s UN Review of the Nuclear Non-Proliferation Treaty. Their petition calls for the review to make “strong and clear conclusions” and for all UN member countries to sign the treaty. Others are conducting related activities.

And the broad national United for Peace and Justice coalition has launched a petition commending President Obama’s statement in Prague last spring that “as the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act,” and urging him to initiate “good faith multilateral negotiations” to end nuclear weapons “within our lifetimes.”

These campaigns are an excellent springboard for everyone concerned about the world’s continuing closeness to the nuclear brink. Now is the time to act for a nuclear weapons-free future!