"Global Zero" has become a well-known slogan to revive the decades-old idea of eliminating all nuclear weapons. Interest in abolition has been renewed by the concern that, in a world with an increasing number of nuclear-armed countries, the use of this most destructive weapon could become ever more likely. With nuclear deterrence we bought time, but it would be a tremendous mistake to believe that deterrence will always work.

There is no doubt that numerous hurdles need to be overcome if we really want to get rid of all nukes. Often-discussed problems include the need for an extremely intrusive verification system as well as improved enforcement mechanisms to ensure compliance with treaty obligations. Another question, often overlooked, is the order in which nuclear weapons should be removed. This issue is extremely important for an alliance such as NATO, which still relies upon extended deterrence provided by U.S. nuclear forces. Today, the U.S. retains about 150-240 nuclear warheads at six bases in Belgium, the Netherlands, Germany, Italy and Turkey. All of them can be delivered by aircraft – either by U.S. bombers stationed in Europe or by aircraft owned by the host countries. This arrangement is known as "NATO nuclear sharing."

In the months ahead U.S. nuclear forces in Europe will be debated much more. There are three reasons for this. First, nuclear disarmament will be on the agenda of the new U.S. President, Barack Obama. Calls by George Shultz, William Perry, Henry Kissinger and Sam Nunn for the U.S. to work toward the elimination of nuclear weapons have sparked an international debate and gained many supporters, including Obama. Second, the 2010 Nuclear Non-Proliferation Treaty (NPT) Review Conference is approaching. Reaching agreement there may involve making concessions on NATO’s nuclear sharing arrangement as some non-aligned countries have long argued that it runs counter to the NPT by providing non-nuclear-weapon states with access to nuclear weapons. Third, NATO is supposed to begin debating a new strategic concept after the NATO summit to be held in Strasbourg and Baden-Baden in April 2009.

Building consensus on the role of nuclear deterrence in general and the stationing of U.S. nuclear forces in Europe in particular will be hard. While "old" NATO members may question the continued relevance of U.S. nuclear forces in Europe, "new" member states worry about Russia and its more assertive foreign policy, exemplified by the Georgia crisis and its announced intention to place nuclear-capable missiles close to the Polish border. NATO members at its Southern periphery – in particular Turkey – may insist that the U.S. should not remove its nuclear weapons in the face of Iran's continued nuclear program and the threat of a nuclear arms race in the Middle East.

This discussion will be complicated by the fact that if nuclear sharing is to be continued, tough procurement decisions would have to be taken by participating countries. Germany, for instance, plans to use its Tornado aircraft for nuclear missions until 2020. By that time, the German Air Force will have put the new Eurofighter into service. But this system will not be certified by the U.S. for nuclear missions, leaving Berlin with no option but to buy an additional American platform if it does not want to get out of the nuclear sharing business. This would be an expensive endeavour that German taxpayers will be unlikely to swallow.

Against this background, it is high time to re-think the rationale of the U.S. nuclear presence in Europe. To begin with, in pure military terms, these systems are not relevant anymore. If a U.S. president were to decide to use nuclear weapons in a crisis, why would he or she decide to use relatively old German Tornados instead of modern U.S. equipment such as B-2 bombers or air-launched cruise missiles? Moreover, the U.S. Air Force seems to be more concerned about possible terrorist attacks on nuclear stockpiles based in Europe than it is convinced of the military relevance of these systems. It would prefer to spend the money currently invested in the protection of nuclear sites in Europe for military projects it deems more important.

At the same time, however, there are a number of political reasons for not entirely foregoing U.S. nuclear forces in Europe at this point in time. The function of these systems is to keep the peace and to prevent wars. In particular, U.S. nuclear forces in Europe and nuclear sharing with Alliance partners demonstrate a shared risk within NATO and binds America to the old continent. At least some NATO partners continue to value this. They remain particularly interested in a strong nuclear deterrent vis-à-vis Russia and Iran. Moreover, the U.S. nuclear presence gives those NATO members participating in nuclear sharing a greater say in nuclear decision making or, at least, more access to information. In order to avoid yet another split in NATO on a crucial issue, these political factors should not be neglected. In addition, three further points need to be taken into consideration.

First: Arms control. In that regard, eliminating all U.S. nuclear forces in Europe does not make much sense. The aim of Soviet as well as Russian political leaders has always been to achieve a Western Europe free of U.S. nuclear weapons without removing its own non-strategic nuclear forces in which it enjoys massive numerical superiority. At a minimum, NATO should use the U.S. nuclear weapons based in Europe as a bargaining chip. However, Russia will not go to zero with its own non-strategic nuclear forces. Moscow perceives them as a counterweight to NATO’s overwhelming conventional superiority and its ongoing expansion ever closer to the Russian border. Today, we do not even know how many non-strategic nuclear forces Moscow possesses, nor do we know where they are located and whether they are appropriately protected against unauthorized use. For NATO, therefore, a more important first step than bringing Russian non-strategic nuclear forces to zero should be enhanced transparency. Removing all U.S. nuclear weapons in Europe without transparency and reciprocal reductions in return would run counter to Western interests.

Second: Nonproliferation within NATO. The U.S. nuclear presence in Europe was always intended to prevent nuclear proliferation within the Alliance. Without a clearly demonstrated nuclear deterrent provided by U.S. nuclear weapons based at Incirlik, Turkey could have further doubts about the reliability of NATO's commitment to its security. Turkey already feels let down by NATO's ambivalent response to its calls for support in the Iraq wars of 1991 and 2003. Sitting on the outer edge of the alliance, facing a nuclear-weapon-capable Iran, and possibly feeling that NATO’s nuclear security guarantee would not actually be extended to it in a crisis, Turkey could seek to develop countervailing nuclear capabilities of its own.

Third: The role of France within NATO. On several occasions, Paris has offered to extend its nuclear umbrella to its European partners. If the U.S. were to remove all its nuclear weapons from Europe, France might feel invited to renew such a proposal. Paris plans to become militarily reintegrated into NATO by 2009. Therefore, a French nuclear contribution to NATO's defence posture might be welcomed. At the same time, however, France has never offered to base a component of its nuclear forces on the territory of allies, nor does it intend to participate in NATO's nuclear planning group. Therefore, many doubt that France could play a role comparable to that of the U.S. Moreover, many Europeans believe that France’s limited nuclear options are insufficient for Europe's nuclear deterrence requirements. Finally, some NATO members, particularly the new ones, simply do not trust France as much as the U.S. when it comes to national security matters. Even though the U.S. nuclear weapons currently based in Europe are not very relevant from a military standpoint, their political impact should not be neglected. A decision to make France responsible for Europe’s nuclear deterrent would therefore cause a tremendous controversy within the Alliance.

So, should U.S. nuclear forces be removed from Europe soon, or should they stay for some more years?

The next step on the road to "Global Zero" will be a follow-on agreement to the Strategic Arms Reduction Treaty (START) to be negotiated between Washington and Moscow. It should not only include low limits for strategic systems, but also move toward including non-strategic systems within lowered limits on total forces, without yet removing all U.S. nuclear forces from European territory. These negotiations can be expected to become extremely complicated. But including non-strategic weapons into formal arms control treaties is inevitable. As history has shown, unilateral reductions, such as those undertaken by Presidents Bush and Gorbachev in 1991 for non-strategic weapons, do not provide for the transparency needed. Some believe that even high-level officials in Moscow have no idea how many tactical nuclear weapons there are on Russian territory.

A START follow-on that reduces both strategic and non-strategic weapons but does not force NATO to end nuclear sharing would avoid bitter discussions within the Alliance that would run the risk of dividing NATO into nuclear supporters and nuclear opponents. Such a debate would weaken the Alliance at a time when it has to tackle complicated tasks such as the military engagement in Afghanistan. At a later stage, maybe within five years of the entry into force of a START follow-on agreement, NATO may decide to either go to zero with all U.S. nuclear forces in Europe or to modernize them. Such a decision would be taken in light of the status of the Iranian nuclear program as well as NATO’s evolving relationship with Russia.

Dr. Oliver Thränert, Senior Fellow, German Institute for International and Security Affairs, Berlin.