The politics of economic recovery have distracted world leaders from the long-term threats that face humanity, specifically the dangers presented by climate change and nuclear weapons, observed the Science and Security Board of the Bulletin of the Atomic Scientists, as it announced today that the minute hand of its Doomsday Clock will remain at five minutes to midnight. "2012 was a year in which global problems pressed forward, but too many of its citizens stood back."

In a rare accord reached on March 25, the European Union decided to conduct safety "stress tests" on all of its 143 nuclear reactors. Akin to earlier stress tests that evaluated whether major banks were robust enough to withstand adverse economic conditions in the aftermath of the global financial collapse, the nuclear safety stress tests will assess the ability of reactors to withstand events such as those that devastated Fukushima.

The nuclear safety "stress tests" planned for Europe should be expanded to include tests that evaluate the security of nuclear materials around the world.

Two years ago in Prague, President Barack Obama laid out his vision of a world free of nuclear weapons. Recognizing that this would not likely be achieved in his lifetime, he outlined practical steps by which the international community might strive for greater security in a world where nuclear weapons still exist. One of these steps was the four-year goal to secure all loose nuclear material -- almost immediately after his speech, concerns about nuclear terrorism and nuclear material security were prominent on the international agenda.

The recent effort to persuade Canada to sign the Treaty on the Prohibition of Nuclear Weapons has stimulated a lively debate in the public sphere. At the same time, out of the spotlight, the start-up company Moltex Energy received a federal grant to develop a nuclear project in New Brunswick that experts say will undermine Canada’s credibility as a nonproliferation partner.

Editor's note: Founded in 1945 by University of Chicago scientists who had helped develop the first atomic weapons in the Manhattan Project, the Bulletin of the Atomic Scientists subsequently created the Doomsday Clock in 1947 using the imagery of apocalypse (midnight) and the contemporary idiom of nuclear explosion (countdown to zero), to convey threats to humanity and the planet.

On March 31, Chinese President Xi Jinping will be among world leaders attending the fourth and last Nuclear Security Summit in Washington, D.C., where they will try to strengthen nuclear security to deal with the evolving threat of nuclear terrorism. Such efforts are badly needed, in light of the facts that there have been approximately … Continued

Neutrons advance a wide variety of human purposes, including helping to manufacture medical isotopes to treat and diagnose deadly diseases. But highly enriched uranium is used in the production of some medical isotopes, which incurs risk that the material will be diverted or stolen for use in nuclear weapons. To maximize the benefits and minimize the risks associated with using neutrons, we need better international coordination. A regular experts’ meeting at the IAEA is just the place to do it.

Why the international community should work toward a binding radioactive sources convention.

The 2010 Nuclear Security Summit in Washington, DC, was a milestone for nuclear security. Political leaders from 47 countries, including the United States, and multilateral organizations gathered to make a concerted global effort to protect vulnerable nuclear material and to prevent nuclear terrorism. Chinese President Hu Jintao -- putting aside China-US disputes over arms sales to Taiwan and the Dalai Lama's visit to Washington -- attended the summit, speaking positively of China's responsible and cooperative attitude toward international security.

Thanks to the participation of Iranian President Mahmoud Ahmadinejad, the eighth conference "to review the operation" of the Nuclear Non-Proliferation Treaty (NPT) is attracting more attention than these affairs usually do. When it concludes on May 28, the NPT Review Conference may not yield a final document expressing the consensus of all 189 NPT member states--but that does not mean the event will be less than spectacular. On only its first day, the conference produced some fireworks.

Too often Washington confronts its national security challenges by installing a "czar" to knock heads and inspire collaboration among government agencies. Here’s why that approach doesn’t work.

A careful review of threats leads the Bulletin's Science and Security Board to conclude that the risk of civilization-threatening technological catastrophe remains high, and that the hands of the Doomsday Clock should therefore remain at five minutes to midnight.

According to recent reports in the New York Times and Washington Post, Pakistan has nearly doubled its nuclear arsenal to more than 100 weapons and appears on track to soon surpass Britain as the world's fifth largest nuclear power.

If the car bomb in Times Square contained just one of the tens of thousands of radioactive sources that exist in the U.S. and it had successfully detonated, this American landmark would be uninhabitable for months or years to come. And, if the attack were with an improvised nuclear device instead, a large portion of Manhattan would have been destroyed. We were lucky in many ways that day, but these are real threats posed by ever-bolder terrorists, and our luck might not last forever.

With Blair’s death, the nuclear-disarmament movement has lost one of its most learned, creative and persistent leaders. Those of us who have had the privilege of working with him will continue to be inspired by his quiet but dogged and comprehensive commitment to the mission.

This month, the Obama administration has greatly accelerated its efforts to reduce nuclear dangers and move all nations toward "the peace and security of a world without nuclear weapons," as President Barack Obama phrased it during his now famous Prague speech.

Since the collapse of the Soviet Union, the need to reassure allies has become, perhaps by default, one of the more important rationales for continuity in U.S. nuclear posture. In fact, a view frequently expressed by current and former U.S. officials holds that Washington still maintains the largest strategic nuclear arsenal in the world precisely to provide these assurances.

As the Obama administration contemplates further changes to US nuclear policy and posture in its second term, it will no doubt encounter opposition from those who argue that the world is too dangerous and complex to permit further reductions in US and global nuclear force levels. Critics will make many assertions in support of their case, but two claims in particular are likely to underpin their defense of the status quo.