The 'leap second' could disappear. How a minor adjustment became a major problem

For more than half a century, atomic time - measured by precise vibrations of atoms - has been kept aligned with solar time by inserting occasional "leap seconds" when the Earth's rotation lags. Those corrections began in 1972 (ten seconds added at once) and have been applied 27 times, typically at the end of June or December, most recently in 2016. An international standards body has voted to stop inserting single leap seconds and instead allow the accumulated difference to reach a full hour (3,600 seconds) before making an adjustment, effectively pushing any visible mismatch between clock time and the sun by centuries or millennia. The change takes effect in May 2027.

The rationale is practical: abrupt leap seconds create interoperability problems for telecommunications, software and infrastructure that rely on tightly synchronized time, and inconsistent implementation across networks can cascade into outages. Leap seconds were implicated in outages at Reddit and LinkedIn in 2012 and a brief Cloudflare outage in 2016; tech firms warned a future "negative" leap second (if Earth speeds up) could be even more disruptive. Some scientists and astronomers accept the trade-off, noting no perfect system exists and the slow drift is manageable, while others argue better engineering could mitigate the issue rather than abandoning the current practice.