The daily timing of a given temperature has shifted by over an hour since 1980

Climate change manifests not only as changes in daily mean temperatures but also as shifts in the daily pattern of temperatures. We analyze historical analogues in the daily temperature cycle by comparing equivalent hourly temperatures since the 1980s. On a global average, temperatures characteristic of the morning warming period occur roughly 15 minutes earlier per decade, while those in the afternoon cooling period occur more than 20 minutes later per decade. For example, temperatures that occurred at 10 AM in the 1980s now occur at 9 AM, with even greater shifts in the afternoon. If sustained, the time of day at which equivalent temperatures occur would be displaced by more than three hours by 2100 relative to the 1980s, persisting under the ‘middle of the road’ pathway but slowing and eventually stopping under mitigation. The timing changes perturb ecological cues, increase human heat exposure, and displace energy demand in ways not captured by means or extremes, underscoring the value of time-of-day metrics for characterizing climate change impacts. Moreover, in more than half of mid-latitude regions, mean daily minima are projected to exceed the 1980s maxima, creating novel diurnal regimes with no recent historical analogues.