( CNN ) -- On Wednesday , President Obama took a meaningful step toward reshaping our nuclear arsenal in line with the reality of 21st-century security priorities . Standing at the Brandenburg Gate in Berlin , he announced that he would seek negotiated cuts with Russia of up to one-third of strategic nuclear weapons as well as address the issue of nuclear weapons stationed in Europe . But we must understand that these proposed reductions are significant only if they are part of an ongoing effort to eliminate nuclear weapons altogether . If they serve to legitimize the indefinite retention of nuclear weapons at an `` acceptable '' level , the specter of nuclear catastrophe will continue to haunt humanity , for arsenals of this reduced size would still inflict unimaginable destruction across the planet . A study by Physicians for Social Responsibility ( PDF ) showed that if only 300 warheads in the Russian arsenal got through to targets in American cities , 75 million to 100 million people would be killed in the first 30 minutes by the explosions and firestorms that would destroy all of our major metropolitan areas , and vast areas would be blanketed with radioactive fallout . In addition , the entire economic infrastructure , on which we depend to sustain our population , would be destroyed . The transportation system , the communications network , the public health and banking systems , the food distribution network -- all would be gone . In the months after this war , it is probable that the vast majority of the American population who were not killed in the initial attack would die of starvation , exposure , epidemic disease and radiation poisoning . Even with Obama 's proposed reductions in nuclear weapons , the United States and Russia would each continue to possess more than triple the nuclear weapons required to cause that devastating scenario . But as unimaginable as these direct consequences would be , the effects throughout the world would be even worse . A recent study by Robock , Oman and Stenchikov ( PDF ) showed that a nuclear war , even with the reduced numbers Obama has proposed , would cause catastrophic global climate disruption ( PDF ) . The firestorms started by these nuclear explosions would loft 50 million to 100 million tons of soot into the upper atmosphere , blocking out the sun . In a matter of days , temperatures around the world would plummet by as much as 20 degrees centigrade -- 36 degrees Fahrenheit -- in the agricultural regions in the interior of continents . The result would be a catastrophic failure of crops throughout the world and a global famine that could claim a majority of the human population . The existential threat to human civilization that nuclear weapons would still pose does not mean these proposed reductions are not useful . On the contrary , they are a critically important step to reduce the nuclear danger , and it is essential that we implement them as rapidly as possible . But we ca n't stop there . This effort must lead to multilateral negotiations involving all nuclear weapons states , negotiations that will produce a nuclear weapons convention banning these weapons once and for all . These negotiations will not be easy , and the treaty they produce will have to be a hard-nosed agreement that establishes mechanisms to verify and enforce compliance . But we do n't have an alternative . Some say it is unrealistic to think we can eliminate nuclear weapons . But in truth , it is unrealistic to think we can maintain nuclear arsenals indefinitely and still avoid a nuclear conflict . The Cuban Missile Crisis 51 years ago brought us to the brink of nuclear catastrophe . Further , we know of at least five occasions since 1979 when either Washington or Moscow prepared to launch a nuclear war in the mistaken belief that they were themselves under attack . The most recent near miss that we know about was in January 1995 , a full five years after the fall of the Berlin Wall . On each of these occasions we were incredibly luck and a national security strategy based on luck is not a wise course of action . As long as there are arsenals of nuclear weapons , we are living on borrowed time . We owe it to our children to eliminate them from the world , and we should start by implementing the modest proposals made by Obama in Berlin this week . The opinions expressed in this commentary are solely those of Ira Helfand and Alan Robock .
President Obama will seek sharing with Russia of up to one - third of nuclear weapons . Writers : No such thing as ` ` acceptable '' exists ; even lesser levels would obliterate humanity . Writers : Nuclear warheads would kill a million ; the rest would die from starvation , too . We can not maintain nuclear arsenals indefinitely and still avoid a nuclear war , they say .