Most policy discussions in the United States concerning what to do about Iran's nuclear program revolve around competing timetables as to when the Islamic Republic is expected to have reached the capacity to fabricate atomic bombs. How much time do we have to let sanctions and international diplomacy do their work before a military option becomes imperative is usually conditioned on whether one expects Iran to reach its nuclear break-out point in one year or in ten years.

But there is another timeline we should be concerned about.

Earlier this week, at a conference on energy security held in Berlin (co-sponsored by the Stiftung Wissenschaft und Politik, The Nixon Center and the German Marshall Fund), a presentation on Europe's growing need for natural gas noted that, by 2025, Europe will face a 25 percent gap between projected demand and sources of supply.

Given that reality, there is only so much time before Europeans will decide that Iran, which has the world's second largest reserves of natural gas, is a critical part of ensuring their energy security. So far, the United States has been largely successful in convincing Europeans to delay proposed investments in Iran's natural gas sector and has expressed strong disapproval of plans to connect Iran to the so-called NABUCCO pipeline (designed to bring Caspian gas via Turkey to Europe).

But NABUCCO has limits. Many Europeans are skeptical that there is enough Caspian gas to really make a difference for their consumption, arguing that between rising demand in the Caucasus and Turkey and increased needs in southeastern Europe, the amount of gas that will end up being available for western European needs once the line ends in Central Europe will be quite small. (On a separate note, Hungary is already giving the green light for a competing project that will allow for GAZPROM to send more of its gas via the Blue Stream route to Turkey and thence to Central Europe, bypassing Ukraine). In the end, I was told, for NABUCCO to make sense, it will have to include gas from Iran.

This means that sooner or later Europe's ability to give Washington support on isolating Iran will give way to its own needs for energy. The first cracks appeared this past week, when Austria's OMV energy group signed a deal pledging $30 billion in investments over 25 years to develop gas fields and to construct a liquefied natural gas (LNG) depot. EU Energy Commissioner Andris Piebalgs, in responding to criticism from Washington, pointed out, "To be fair, I'd say to OMV no United Nations resolution prevents them from doing this." Already, Iran sees this deal as a way to further influence in Europe. The head of the Iranian Majlis's (Parliament's) Committee on National Security and Foreign Policy, Alaeddin Boroujerdi, said in a meeting in Sofia, Bulgaria, "Given that Bulgaria is situated on the route of an Iran-Austria gas pipeline, the project provides Bulgaria with a golden opportunity for cooperation."

Some Europeans that I have spoken with privately feel that, for the next two years or so, Europe can afford to continue to support Iran's economic isolation, but that, starting in the next decade, growing pressures to secure new supplies of energy will lead more European firms to begin investing in Iran to ensure that, by the 2020s, the infrastructure is in place for large-scale Iranian shipments of gas to Europe.

I pressed my interlocutors further-was this is a case of advising, "Whatever you do, do it quickly"-meaning that if the United States were to pursue forcible regime change the preference would be to do it sooner? They demurred. But the underlying impression I received was that, say, by 2011 or 2013, large-scale European investment in Iran will begin no matter whether it is still the Islamic Republic or some other form of government-and that Washington is faced with two clocks counting down with regard to its freedom of action vis-à-vis Tehran.

Nikolas Gvosdev is editor of The National Interest.