Lassina Zerbo, CTBTO executive secretary. Credit: CTBTO

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) was designed in the 1990s to end the testing of nuclear devices. Although the treaty has been signed by 183 countries, it has yet to enter into force because some key countries — notably the United States — have yet to formally ratify it. 

In the meantime, to set up a mechanism for enforcing the treaty, the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), based in Vienna, has been building a global network of monitoring stations that could detect any violations. These include seismic, infrasound (frequencies to low to be heard by the human ear), hydro-acoustic and radionuclide sensors that would alert member states that a device has been detonated anywhere on the planet. The network now includes some 300 stations and is about 90% complete — and gathering data at full steam. It has monitored a de-facto moratorium on nuclear testing that has been observed by nations since the late 1990s, with the exception of North Korea. (In 2013, CTBTO sensors were instrumental in confirming that North Korea detonated a nuclear device.)

But the CTBTO has also opened up its data to scientists. Applications have ranged from tracking large storms or clouds of volcanic ash to monitoring the drift of large icebergs. CTBTO sensors also showed that the meteor that exploded over Chelyabinsk, Russia, in 2013 was the largest to hit Earth in at least a century.

Ahead of a 22–26 June conference in Vienna to discuss these scientific applications, Nature spoke to CTBTO executive secretary and geophysicist Lassina Zerbo, who spearheaded the opening up of the organization’s data when he was head of its data centre.

How did the CTBTO begin to open up to research?

When I joined the organization in 2004, we had what we call a task force on data confidentiality. At the time I pointed out that when you have a network growing all over the world, the only way you can keep it growing and remain relevant is to share. The first contract for the use of our Virtual Data Exploitation Centre was signed in February 2011.

Then the Fukushima disaster in Japan, in March 2011, was an opportunity for people to know about our network. We contributed to give an early warning of the tsunami. And infrasound was what confirmed the explosion of the power plant itself. Then, our network tracked the dispersion of radioisotopes around the globe. Our member states requested that we start to cooperate more with the International Atomic Energy Agency to share data about nuclear disasters.

Can you give some other examples of how CTBTO data has helped scientists?

If you use our data, which is reliable, precise and efficient, you often manage to locate the epicentre of an earthquake with more precision than with open data such as those from the US Geological Survey's network.

Our infrasound stations can also detect a plane crash. The Air Algérie flight between Burkina Faso and Algeria that crashed in Mali last July was detected by our station in Cote d’Ivoire, 960 kilometres from the impact of the aircraft. CTBTO seismic-acoustic officer Mark Prior also tried to help in the search for Malaysia Airlines flight MH370, which disappeared in the Indian Ocean last year. Unfortunately, at this point in time we have no evidence, but the research has not stopped.

We’re also helping to see how marine mammals are moving. We can help to follow whales with hydroacoustic and infrasound data.

Does sharing data benefit the CTBTO itself?

If you make your data available, you connect with the outside scientific community and you keep abreast of developments in science and technology. Not only does it makes the CTBTO more visible, it also pushes us to think outside the box. If you see that data can serve another purpose, that helps you to step back a little bit, look at the broader picture and see how you can improve your detection.

The United States and Russia are reportedly spending billions of dollars on modernizing their nuclear stockpiles. Some worry that Russia in particular might be tempted to break the moratorium. Do you think Russia is still committed to the test-ban treaty?

I can only rely on what officials of those countries tell me. I met Russian foreign minister Sergey Lavrov twice. I asked him that question. He said that Russia is so committed that it will make sure that the portion of the network that is on their soil will be completed in two years. Also, Russia has ratified the CTBT, but the United States has not.

In 1999, the US Senate refused to ratify the test-ban treaty, which had been signed by then-President Bill Clinton. What did the sceptics say, and what could make them reconsider?

One thing that people were saying was that this treaty is not verifiable. But the performance of the international monitoring system is going far beyond what was anticipated during the negotiations. The CTBTO is the only system and institution that can give any legitimacy to a detection. We’re 'proving by doing' that the treaty is verifiable.

Iran also has signed the test-ban treaty but not yet ratified it. What part can the treaty play in the ongoing negotiations between Iran and the West on its nuclear programme?

I think CTBT ratification by Iran will give assurance — with teeth — that Iran is not seeking to develop nuclear weapons. This could have been a way out for Iran right before this negotiation, because if you ratify you are basically saying, “I will not do tests to develop nuclear weapons at all”. I think we have to go on a step-by-step approach to build confidence to see if we can get them into that process of ratification. I am confident that in the end the CTBT will play an important part in that diplomatic and confidence-building process with Iran.

Would the network of sensors ever be discontinued: for instance, if the test-ban treaty were to fall apart?

I can confidently say that this is almost impossible. For almost 20 years now, the international community has invested over US$ 1 billion in our system; they use our data on a daily basis, and not only for verification purposes. Our member states have an interest to preserve this investment that is already serving the international community so effectively.