June 30 brings another leap second to our global atomic clocks, in order to account for the slowing rotation of our planet. I remember the first leap second I paid attention to, on January 1, 1988, when the International Earth Rotation and Reference Systems Service (IERS) took over the responsibility to scheduling and coordinating leap seconds. 

When the United Kingdom finally joined the rest of Europe in adopting the Gregorian calendar in the 1750's, there were riots by people who were convinced the government had stolen two weeks of their lives in a Papist plot! A second or two, added to the year every now and then, probably doesn't represent an existential threat to the planet.