The year just past proved perilous and chaotic, a year in which many of the risks foreshadowed in our last Clock statement came into full relief. In 2017, we saw reckless language in the nuclear realm heat up already dangerous situations and re-learned that minimizing evidence-based assessments regarding climate and other global challenges does not lead to better public policies.

Although the Bulletin of the Atomic Scientistsfocuses on nuclear risk, climate change, and emerging technologies, the nuclear landscape takes center stage in this year’s Clock statement. Major nuclear actors are on the cusp of a new arms race, one that will be very expensive and will increase the likelihood of accidents and misperceptions. Across the globe, nuclear weapons are poised to become more rather than less usable because of nations’ investments in their nuclear arsenals. This is a concern that the Bulletin has been highlighting for some time, but momentum toward this new reality is increasing.

As you will see in the discussion that follows, the Bulletin’s Science and Security Board has once again assessed progress—actually, lack thereof—in managing the technologies that can bring humanity both relief and harm. It is my hope that the statement focuses world attention on today’s dangerous trajectory and urges leaders and citizens alike to redouble their efforts in committing to a path that advances the health and safety of the planet.