When presidents Barack Obama and Dmitry Medvedev meet today for the first time, they will have an historic opportunity to confront the most urgent security threat to our world: the proliferation of nuclear weapons and the risk of nuclear terrorism. The two leaders can move beyond traditional arms control and, in a bold move, set the world on a course towards the total elimination of all nuclear weapons - global zero.

In London, they should agree that the US and the Russian Federation will begin work immediately to achieve an accord for deep reductions in their arsenals and then lead a longer-term effort with other nuclear powers to eliminate all nuclear weapons worldwide through phased and verified reductions.

Today nine countries have more than 23,000 nuclear weapons, many of which are programmed to launch in minutes. A nuclear conflict - or accident - could cause millions to die in a flash and create an environmental catastrophe that would last for generations.

Terrorist groups have been trying to buy, build or steal nuclear weapons, and in the last two decades there have been at least 25 instances of nuclear explosive materials being lost or stolen. If terrorists were to get their hands on a bomb and explode it in a big city, hundreds of thousands of people would die instantly.

We believe that whatever stabilising impact nuclear weapons may have had during the Cold War, in the new security environment of the 21st century any residual benefits of these arsenals are overshadowed by the growing risks of proliferation and terrorism.

In response, we, along with more than 100 others, have formed Global Zero, an international, non-partisan initiative dedicated to achieving a binding, verifiable agreement to eliminate all nuclear weapons. Many of us have worked at senior levels with issues of national security in the nuclear weapons states and key non-nuclear countries. Our group includes nine former heads of state; eight former foreign ministers from the US, Russia, Britain and India; three former defence ministers from the US and Britain; six former national security advisers from the US, India and Pakistan; and 19 former top military commanders from the US, Russia, China, Britain, India and Pakistan. With a clear, realistic and pragmatic appreciation of the challenges of achieving our goal, Global Zero is developing a step-by-step plan for getting to zero.

This will not happen overnight nor unilaterally. Getting to global zero will require the reduction of all nations' arsenals over many years. Because American and Russian stockpiles account for 96 per cent of the world's nuclear weapons, these two countries should begin with deep reductions to their arsenals, while beginning a dialogue with the other nuclear weapons states. Clearly, multilateral negotiations for global zero with China, France, India, Britain, Pakistan and Israel must deal effectively with concrete national and regional security concerns. Progress on this agenda will be accelerated if the pressing issues of preventing Iran from acquiring nuclear weapons and getting North Korea to relinquish its nuclear arsenal are solved. A commitment by nuclear powers to begin serious negotiations for global zero would strengthen the case against any non-nuclear nation that strives to acquire nuclear weapons.

Needless to say, this is an ambitious agenda, so it is important to begin now. The usual arms control approach and half-measures will not suffice while nuclear weapons spread and terrorists work to obtain them. A far-reaching joint initiative by presidents Obama and Medvedev would fortify the 2010 Non-Proliferation Treaty Review Conference, bolster existing efforts to prevent and roll back proliferation, and set the stage for the first ever multilateral negotiation on nuclear reductions. This is only a beginning, but it sets the course for the world's future.

So far, the statements out of both Washington and Moscow are reassuring. Last July, Mr Obama said: “It is time to... stop the spread of nuclear weapons; and to reduce the arsenals from another era. This is the moment to begin the work of seeking the peace of a world without nuclear weapons.” This month, Mr Medvedev declared that his country “is fully committed to reaching the goal of a world free from these most deadly weapons”.

They and a growing number of hard-nosed realists around the world understand that, as long as nuclear weapons exist, they will continue to spread, increasing the chance that they will be used. Total elimination of all nuclear weapons is the only real solution.

If presidents Obama and Medvedev seize this historic moment, a new generation will look back on April 1, 2009, as the moment when two leaders confronted the greatest threat to our survival, the nuclear shadow of the last century began to lift and our course was set toward a world without nuclear weapons.

The six co-authors of this article are: Chuck Hagel (former US Senator), Igor S. Ivanov (former Minister of Foreign Affairs, Russia), Richard R. Burt (former US Chief Negotiator, Strategic Arms Reduction Talks), Igor Yurgens (Chairman of the Institute of Contemporary Development), General John J. Sheehan (former Commander in Chief, United States Atlantic Command) and Colonel-General Evgeny Maslin (former Chief of the Main Directorate, Russian Ministry of Defence - was responsible for the security of Russia's nuclear arsenal).

The full list of signatories to Global Zero is: James Arbuthnot, Lloyd Axworthy, K. Shankar Bajpai, Hugh Beach, Margaret Beckett, Lawrence Bender, Sandy Berger, Alexander Bessmertnykh, Ela Bhatt, Carl Bildt, Robert Blackwill, Lakhdar Brahimi, Richard Branson, Zbigniew Brzezinski, Gro Harlem Brundtland, Richard Burt, Richard Butler, Fernando H. Cardoso, Frank Carlucci, Jimmy Carter, Naresh Chandra, Raymond Chambers, Joseph Cirincione, Richard Cizik, Liru Cui, Ivo Daalder, Romeo Dallaire, Tarun Das, Jayantha Dhanapala, Michael Douglas, Lawrence Eagleburger, Rolf Ekéus, Tetsuya Endo, Gareth Evans, Jake Garn, Hans-Dietrich Genscher, Jamshyd Godrej, Mikhail Gorbachev, Thomas Graham Jr, Chuck Hagel, Lee Hamilton, David Hannay, Gary Hart, Stanley Hoffmann, Charles Horner, Liming Hua, Douglas Hurd, Wolfgang Ischinger, Igor Ivanov, Max Kampelman, Sergei Karaganov, Jehangir Karamat, Yoriko Kawaguchi, Bob Kerrey, Shaharyar Khan, Alan Khazei, Konstatin Kosachev, Roland Lajoie, Anthony Lake, Ruud Lubbers, Mikhail Margelov, Evgeny Maslin, Talat Masood, Jack Matlock, Robert McFarlane, Robert McNamara, Merrill McPeak, Brajesh Mishra, Amr Moussa, Satish Nambiar, Klaus Naumann, Queen Noor, Pam Omidyar, David Owen, Zhenqiang Pan, Guangqian Peng, Thomas Pickering, Vasantha Raghavan, Fidel Ramos, Malcolm Rifkind, Mary Robinson, Michel Rocard, Henrik Salander, Yukio Satoh, Jack Sheehan, Jennifer Allen Simons, Jaswant Singh, Jeffrey Skoll, Mário Soares, K. Subrahmanyam, Strobe Talbott, Toshiyuki Takano, Horst Teltschik, John Thornton, Desmond Tutu, Shashindra Pal Tyagi, Ehsan ul-Haq, Evgeny Velikhov, Shirley Williams, Jianmin Wu, Xuetong Yan, Jiemian Yang, Muhammad Yunus, Philip Zelikow and Anthony Zinni.

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