As world leaders prepare to gather in Washington, D.C., for the fourth and final Nuclear Security Summit,they can cite progress on their collective pledge to protect vulnerable nuclear materials from theft by terrorists seeking weapons of mass destruction and to build a robust nuclear security system involving all states in the ongoing protection of dangerous nuclear materials. Since early 2010, a dozen countries have eliminated weapons-usable nuclear materials from their territories, dozens more have strengthened their nuclear security practices and policies, and a key international treaty is closer to entry into force.

Even as the global threat environment has worsened,progress on the goals set during the first three summits has slowed, according to the results of the 2016 NTI Nuclear Security Index (NTI Index).  Since 2014, no improvements have been made in the core protection and control measures assessed by the NTI Index; across the entire Index, 43 improvements have been made since 2014, compared with 59 improvements found in the 2014 NTI Index.

In addition, the 2016 NTI Index finds that only one state from the “theft ranking” for countries with one kilogram or more of weapons-usable nuclear materials, Uzbekistan, has removed its materials in the past two years—compared with seven states that had removed their materials in the two years before the 2014 NTI Index was published. Jamaica, which already had less than one kilogram of weapons-usable nuclear materials, also removed its materials.

Finally, the NTI Index identifies a trend toward a plateau or even an increase in nuclear material stockpiles, with the end of the U.S.-Russia HEU Purchase Agreement and with India, Japan, the Netherlands, North Korea, Pakistan, and the United Kingdom all increasing their stocks of weapons-usable materials.

In addition, the current global nuclear security system still has major gaps that prevent it from being truly comprehensive and effective. For instance, no common set of international standards and best practices exists, there is no mechanism for holding states with lax security accountable, and the legal foundation for securing materials is neither complete nor universally observed.

Without a comprehensive and effective global system, states’ approaches to nuclear security vary widely, thereby creating dangerous weak links that terrorists could exploit as they seek the easiest path to weapons-usable nuclear materials.

Given the global challenges in the past two years—from an increase in terrorist atrocities in the Middle East to deepening tensions across the Euro-Atlantic region to the complex negotiations over Iran’s nuclear program and threats out of North Korea—there’s no question that it has been a challenging time for governments to keep nuclear materials security atop their priority lists.

It is also fair to acknowledge that six years is a relatively short time in which to initiate and execute major changes in the perception of threats and priorities. At the same time, leaders must show even greater resolve today in the face of escalating threats.

In addition to continuing the “theft ranking,” the 2016 NTI Index assesses for the first time the potential risks to nuclear facilities posed by sabotage and both rankings including measures relating to cyber attack.

Excerpted from the NTI Index report.