At the height of the Fukushima Daiichi nuclear crisis in 2011, whose second anniversary passed on March 11, journalists and the public learned swiftly about the invisible plume of radioactive particles spilling from stricken reactors at the Tepco power station.

They could follow animated models of the sinuous cloud as it billowed from the site on the northeast coast of Japan and swirled across the Pacific. For the first time in such a crisis, the modelling drew on the analysis of the Comprehensive Nuclear-Test-Ban Treaty Organization’s (CTBTO) worldwide system that monitors the planet for nuclear weapons tests.

The data may not have helped the thousands of people who followed the radioactive plume north as they fled their homes in the Fukushima—critics charge that the Japanese government withheld vital information that could have led them out of harm’s way—but they offered the international community a way to independently assess the extent and the levels of contamination.

Televisions networks around the world broadcast the CTBTO’s animated models during the crisis. They weren’t designed for that purpose (the intent was merely to inform the group’s 183 member states), but they fit the bill perfectly and proved to be 95 percent accurate, according to CTBTO Executive Director, Tibor Tóth.

The availability of the organization’s data is an indication of increasing public access to the type of sensitive scientific data formerly restricted to military and national security organizations, however, it also present new challenges for journalists in terms of handling and interpreting the additional data.

In 1996, ten years after the Number Four reactor at the Chernobyl power plant blew up, world governments began to ink the first major nuclear non-proliferation treaty to emerge at the end of the Cold War. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions without exception.

Eight nuclear powers, including the United States, still have to ratify the pact before it becomes international law, but more than $1 billion has already been invested in its International Monitoring System (IMS), and its global verification regime is nearing completion.

That the treaty would become instrumental in lifting the lid on formerly restricted data may not have been foreseen when it was negotiated, but that was the effect that I witnessed during the my time as a press officer at the CTBTO’s preparatory commission, where I worked from 2009 to 2012.

Currently, the IMS has 274 certified stations worldwide, and 63 more on their way, which use four monitoring technologies: Seismometers to detect earthquakes; infrasound facilities to detect sub-audible waves; hydro-acoustic monitors under the sea; and atmospheric sniffers that snag radionuclides and detect the gases associated with a nuclear explosion.

The CTBTO downloads 10 gigabytes of data per day into the servers at its headquarters in Vienna, and after some processing and analysis, the information is sent to member states in the form of lists of events, bulletins, and reports. Members can use that information at their discretion (by calling for an investigation of suspected nuclear test, for example), but for a long time there was resistance to releasing it to the public.

After the Indian Ocean tsunami struck in 2004, member states realized that the CTBTO’s data could have helped sound the alarm, and soon, they began to allow the use of the group’s data for disaster mitigation purposes. Since 2005, the CTBTO has been providing data to tsunami warning centers from its seismic and hydroacoustic network in collaboration with the United Nations Educational, Scientific and Cultural Organization (UNESCO), adding precious minutes to alerts.

Likewise, during the Fukushima nuclear crisis, several CTBTO members decided that the public’s right to know justified sharing its monitoring data. In Austria, where anti-nuclear sentiment is strong and memories of Chernobyl remain fresh, the government had little hesitation. Its metrological and seismic service, ZAMG, posted the CTBTO data on its website and received hundreds of thousands of hits.

“People wanted to know what was happening,” said Alexander Kmentt, director for Disarmament and Arms Control in Austria’s Federal Ministry for European and International Affairs, in a telephone interview from his office in Vienna. “Information was extremely scant. When it became clear the CTBTO had data, there was a very short discussion on whether or not the information—if considered relevant from a technical point of view should be made public—and we said, yes.”

The governments of Germany and the Philippines later joined Austria in releasing CTBTO data, which were swiftly seized upon by the world’s media. In the days that followed the start of Japan’s nuclear crisis, over 600 outlets cited the data, according to the CTBTO’s log.

Peter Rickwood is founder of Atomic Reporters, a non-profit organization dedicated to supporting journalists covering nuclear issues, particularly in less industrialised countries. A former reporter with The Toronto Star, he served as a press officer for the International Atomic Energy Agency from 2001 to 2009 and subsequently assisted the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) and the UN Scientific Committee for the Effects of Atomic Radiation (UNSCEAR) in working with journalists.