Under the auspices of a proposed international ban on all nuclear-weapons tests, scientists have built a system that can detect an illicit explosion anywhere in the world. The monitoring network stretches from Antarctica to Siberia and captures a wealth of useful data — not just on infrequent atomic bangs, but also on other types of explosion, earthquakes, underwater shocks and radiation releases.

Yet access to these data is restricted to contributing governments and selected allied scientists, who are largely prevented from sharing the information with the public. The diplomatic excuses offered for this unwise and unnecessary secrecy no longer wash, particularly in light of the March meltdowns at the Fukushima Daiichi nuclear power plant. At a meeting in Vienna next week, scientists who used these data to inform their governments about the scale and dangers of the Fukushima accident, but who saw the results kept under wraps, will push for change.

Their move deserves support. Data from the network, run by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), should be freely available to scientists everywhere, for study in their own right and to inform the public in times of crisis. Governments may be nervous about such openness, but the benefits far outweigh the risks.

Scientists were asked to give assessments of the fallout from the Fukushima plant, yet few had access to data that would allow them to do so.

The CTBTO has proved its worth in recent years. It detected North Korean nuclear tests in 2006 and 2009, and has captured detailed seismic data on major earthquakes, including the 2004 Sumatra–Andaman event that sparked a devastating tsunami.

This spring, the organization's 80 radioisotope-monitoring stations offered the clearest global picture of low-level fallout released from the Fukushima plant. Government-accredited scientific institutions were given access to provide politicians with valuable information about how the radiation was spreading and whether it posed a national threat. But most were told not to talk about the results in public, or to share the data with others in academia. The reason was diplomatic: governments such as the United States did not want to embarrass the Japanese, nor pre-empt their announcements about events unfolding at Fukushima Daiichi.

More generally, governments worry that radioisotope data are too sensitive to share. Politicians fear that, should a nuclear test occur, full access to incriminating data could somehow allow the offending nation to contest charges of weapons testing. Or perhaps that others could glean sensitive nuclear secrets from the isotopes in the atmosphere.

These fuzzy fears must be weighed against the impact of the information vacuum that followed Fukushima. Scientists everywhere were asked to give assessments, yet few had access to data that would allow them to do so. Providing open access to the CTBTO's network would have given experts the information they needed to make important statements about Japan's reactors and the threats these posed to Tokyo and beyond. The data would also have lent credibility to the Japanese government's own statements on radiation levels in the region.

Moreover, such data are scientifically useful in their own right. Atmospheric scientists use radioisotopes widely and the CTBTO network is gathering a unique data set that could be used to improve climate models or to refine meteorological studies. Scientists with access to the data might also find some new use for them. Thus far, nations have paid a combined US$1 billion for the network, and they might as well put it to good use.

The network has already taken tentative steps towards openness. Following the 2004 tsunami, member states agreed that its seismic and hydroacoustic data could be used by accredited tsunami-warning centres around the world. In the immediate aftermath of the Fukushima Daiichi accident, it was allowed to share data with the International Atomic Energy Agency.

These are positive developments, but nations should go further: the CTBTO data are valuable in times of both calm and crisis. Contrary to the concerns of some, the more people who see them, the more valuable they will become.