We all know that a day on planet Earth lasts 24 hours – except it isn’t. In fact, there are a few fractions of a second left, which is why we have February 29th every four years. However, the Earth is not a clock, and the actual length of a day can vary slightly. Scientists now say the days have started to get shorter as the Earth spins faster, which could require further, potentially confusing adjustments.
Before you stress about another existential threat to the future of the planet, scientists do not believe that the high rate of rotation is a danger. The mechanisms for this effect are well understood. Factors such as monthly gravity, snow levels and mountain erosion can affect how fast the globe rotates. The effect is that the days can be a few milliseconds shorter or longer than the number 84,400 we use to keep track of time.
In the last few decades, the availability of accurate atomic clocks has allowed humanity to make more precise adjustments to the measurement of our time. For example, several times, I added a “second leap” to keep the clocks aligned out of the traditional leap year adjustment. Since we started measuring time this way, the length of days has evolved more, usually by a fraction of a millisecond. However, this trend has now been reversed.
Scientists note that the days of the last year have been on the shorter side by the same small edges. However, July 19 was a significantly shorter day, with 1.4602 milliseconds below standard. The previous record for the shortest day was set in 2005, but was broken 28 times in 2020.
If this trend continues, we may need one negative jumped second in the next few years to keep our clocks in sync with “real time.” This would be a first, as all previous adjustments have added time. Although it is impossible to say with certainty that this acceleration will continue, most scientists believe that it will continue. Regardless, faster rotation is not a problem – the causes could be, however. Some have begun to wonder aloud whether large-scale changes in global warming have begun to have a visible impact on rotation. Laughter a few milliseconds a day won’t hurt anyone, but it’s not a good sign.