When President Obama speaks at ground zero in Hiroshima on Friday, he must do more than recall the horrific consequences of the first atomic bombing.

Seven years ago, on April 5, 2009, President Obama declared to the world: “As the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act. We cannot succeed in this endeavor alone, but we can lead it, we can start it. So today, I state clearly and with conviction America’s commitment to seek the peace and security of a world without nuclear weapons.”

His record of progress toward that goal is mixed. It is true that this administration negotiated the New START agreement with Russia and soon both sides will have reduced deployed strategic warheads to 1,550 each. Yet this is still vastly more than enough to destroy all that we cherish in our fragile world.

Shockingly, more than half of U.S. and Russian nuclear weapons remain on hair-trigger alert on submarines and in missile silos. Whether as a consequence of miscalculation or accident, they are ready to be launched in less than 15 minutes and able to destroy their targets across the globe 30 minutes later.

In 1986, the New England Journal of Medicine devoted an entire issue to the health consequences from any use of nuclear weapons. Dr. Arnold Relman, then editor of the journal, wrote: “What we physicians urgently need to be telling our government and our fellow citizens is that even 1 percent (or less) of the total destructive power now in possession of the superpowers is enough to doom our two countries and inflict untold damage on the rest of the world. … That is why most physicians … agree that our government ought to be exploring every possible initiative to achieve an agreement on the early reduction of nuclear stockpiles.”

Our nuclear arsenals have been reduced significantly over the past 30 years. Yet in a nuclear war with Russia involving just a fraction of current arsenals, millions of Americans would still be killed and our entire economic, medical and public health infrastructure would be destroyed.

Equally frightening, we have learned that detonation of a small number of warheads anywhere in the world (for example, in a war between India and Pakistan) would result in catastrophic consequences for all of us. In a series of professional journal articles, Rutgers environmental scientist Alan Robock, University of Colorado atmospheric and oceanic scientist Owen Brian Toon and others document that the likely impact of a so-called “limited nuclear war” on climate and global food production would put the world’s population at grave risk of mass starvation.

Certainly, there are many urgent national security threats that must be dealt with. However, these doomsday weapons are simply unusable in addressing any of them.

Without public debate and with our leaders ignoring the reality of the threats nuclear weapons pose to us all, we are now on the verge of an unnecessary, expensive and terribly dangerous new nuclear arms race.

President Obama has proposed and Sens. Susan Collins and Angus King are supporting spending a trillion dollars over the next 30 years on a nuclear weapons spending binge, including new land-based missiles, bomber aircraft, ballistic missile submarines and cruise missiles. This ill-conceived plan is leading the world in exactly the wrong direction.

President Obama will soon be in the perfect location to announce his intention to lead the world back from this brink. The Humanitarian Pledge, supporting legally prohibiting nuclear weapons, has been signed by 127 countries. This month in Geneva, preliminary steps are being taken to begin negotiations on such a treaty. On Friday in Hiroshima, President Obama should announce that the United States will join these negotiations.

While these negotiations move forward, President Obama should demonstrate that the United States is prepared to do more than talk. He should announce that he is ordering our nuclear weapons be taken off hair-trigger alert and challenge Russian President Vladimir Putin to do the same.

With just eight months left in Obama’s presidency, we’re about to find out if his legacy will include real progress toward a world free of nuclear weapons or the beginning of a dangerous new nuclear arms race putting our survival at risk.

When it comes to nuclear weapons policy, we and our elected leaders face a fundamental choice. We choose life.