Joseph Cirincione is president of Ploughshares Fund, a global security foundation, and a member of Secretary of State John Kerry's International Security Advisory Board and the Council on Foreign Relations. He's also the author of "Bomb Scare: The History and Future of Nuclear Weapons." We spoke this afternoon. 

(Photo by Chip Somodevilla/Getty Images)

Ezra Klein: You spend your days trying to rid the world of nuclear weapons. So is today a good day for you? A bad one?

Joe Cirincione: I opened up a bottle of champagne when I heard the news. This is huge. I was at an international security conference in Halifax when the news broke and there were dozens of us celebrating. Rightly or wrongly, Iran is seen as the most serious nuclear threat in the world. Anything you can do to reduce that threat is a major step forward.

EK: Does this actually reduce the threat they pose? Certainly Israel doesn’t seem to think so.

JC: This addresses the major threat that Prime Minister Netanyahu warned the world about in September 2012. He went to the dais of the U.N. General Assembly and he held up a cartoon drawing of a bomb and drew a red line across the top. He warned the world that Iran would soon have enough uranium enriched to 20 percent and that they could quickly, in weeks or months, make a bomb.

His concerns were well-founded. Iran now has about 190 kilograms of this enriched uranium. If they got to 240 kilograms, they'd be very close to a bomb. This deal drains the uranium from Mr. Netanyahu’s bomb. It drains the amount of 20 percent enriched uranium [Iran has]. It makes it much less likely Iran could break out and make a bomb. And it goes further: It stops the manufacturing of new centrifuges. It changes the inspection regime from weekly to daily. If Iran wanted to do anything suspicious, there’s a high probability we'd know about it and could act instantly to stop them.

EK: What’s the counterfactual here? Imagine this deal wasn’t struck and things simply kept on trend. Where would this issue be going?

JC: If Iran hadn’t paused, in a matter of months they would cross Israel’s red line. In perhaps a year they could’ve constructed a crude nuclear device. In another year, they could construct a warhead to put on a missile. While we might think we had two years or so to act, Israel doesn’t look at it that way. They wanted to kill the nuclear baby in the crib. So the alternative to this deal was war.

We shouldn’t kid ourselves. There’s no sanction regime known to man that’s been able to coerce a country into compliance. So if you don't like negotiating with Iran, what you're really saying is you want to go to war. We should be clear-eyed about this. We shouldn’t think there’s some better deal out there.

EK: Israel and some other skeptics argue that diluting the uranium doesn’t mean much because Iran can quickly enrich it again.

JC: Not clear. There’s a lot of doubt that Iran has the capability to convert uranium oxide back to uranium gas. In any event, if they did it we would see it. That’s the benefit of the daily inspections.

EK: Are you confident those inspections have full visibility into the program?

JC: The core part of the inspections is measuring what goes in and what goes out. All the information we have around Iran’s stockpile comes from these IAEA inspections. This is what they do. It’s a lot like accounting. And you can have a pretty high confidence that we know what’s going on at the facilities. The uncertainty is around the question of secret facilities. This arrangement doesn’t help with that. But this is the first phase. In a final agreement, Iran is open to a much tougher inspections regime that allows inspectors to go anywhere at anytime and see anything.

EK: Are you optimistic that we'll get to a final deal after this pause? 

JC: This deal doubles Iran’s breakout time to a nuclear weapon and makes it much more likely that we would see them doing it. It also freezes the program in place. And while we're watching them they can't substantially enhance their capabilities. So we don't lose anything in this deal. And all we’ve given up is a small amount of Iran’s money that we had frozen. The estimates are that they'll receive $7-$10 billion in relief. But they have more than $100 billion still frozen abroad. And all the sanctions on their oil trade and their financial system and their banking still apply. If Iran wants to get back to selling two million barrels of oil a day, they need to finish the final deal and satisfy us that they're giving up their weapon options here.

EK: One argument that Jeffrey Goldberg makes is that another objective of this deal was stopping Israel from making any sudden moves. Now that there’s a deal in place, Israel can’t simply blow up the international community’s negotiations and launch an attack. Do you agree?

JC: I think it’s almost impossible for Israel to launch a military strike on Iran right now. They're isolated. The prime minister is issuing some very tough statements but as far as I can see, he’s the only world leader issuing them. Even Saudi Arabia, which has serious qualms about the deal, is issuing positive statements at the start.

EK: To zoom out, a few months ago a deal was struck to begin breaking down Syria’s chemical weapon capabilities. Now there’s the beginning of a process to potentially end Iran’s pursuit of nuclear weapons. It seems like an unusually good time for anti-proliferation efforts.

JC: It pays to be a pessimist in national security. You get rewarded for painting worst-case scenarios. But every once in awhile you have to evaluate the facts on the ground. And the facts right now are breaking in America’s favor. In the last few months Secretary of State John Kerry has crafted agreements to eliminate Syria’s chemical weapons arsenal. Now there’s an agreement that might eliminate Iran’s nuclear weapon. This looked impossible several months ago.

The significance of all this goes beyond just weapons. One level, of course, is we're reducing major threats that could have killed hundreds of thousands of people. Second, it is being crafted in partnership with countries like Russia, which is creating a better dialogue and working relationship with them. Third, if there’s a rapprochement with Iran, it could pay much bigger dividends in the Middle East, including stabilizing Afghanistan and ending the civil war in Syria. It won't make us BFFs with Iran, but perhaps, as President Rouhani says, we could manage our differences in much the same way that Nixon managed our differences with China.