July ocean heat hit a monthly record while hourly data hid extreme heat on ordinary days
Copernicus put July sea surface temperature at a record 20.96 degrees Celsius, while hourly land data show 28 per cent of extreme-heat hours fall outside days that daily measures call hot.
Science··Midday
A monthly sea-surface high for July
The European Union's Copernicus Climate Change Service reported an average sea surface temperature of 20.96 degrees Celsius outside the polar regions for July 2026. That value sits 0.58 degrees above the 1991-2020 average and is the warmest July in the measurement series. Global average air temperature came in at 16.9 degrees Celsius. Air temperature tied July 2024 for second place and stayed just below the 16.95 degrees Celsius of July 2023, so the ocean figure leads the month more clearly than the air figure does. Copernicus attributes much of the ocean warmth to El Niño conditions in the tropical Pacific, which means part of the sea-surface number comes from a cycle that will turn. The same month brought Europe a third consecutive month of extreme heat, with drought and unprecedented wildfires across the west and centre of the continent. The product is a monthly ocean-surface average for waters outside the polar regions, not a daily map of heat stress over land. It answers how warm the bulk of the ice-free ocean surface was in July as a single period mean.[1]
Hourly extreme heat that daily thresholds miss
Weilin Liao and colleagues, writing in Nature Climate Change, worked through global hourly temperatures from 1981 to 2023 and counted an hour as extreme when it passed the 90th percentile for that hour of the day in 1981 to 2010. Global land averaged about 269 such hours per summer, and more than 80 per cent of land showed an increase averaging 62 additional hours per decade. Under the high-emissions SSP5-8.5 pathway the projections add more than four extra hot hours to hot days by 2070 to 2099, and three extra extreme-heat hours to days that would not be counted as hot at all. Low- and middle-income countries carry more than three-quarters of both current and projected exposure. The figure that matters for warning systems is the 28 per cent of extreme-heat hours already falling outside days that daily measures call hot, because most alerts rest on a daily threshold. The authors say the mechanisms behind these short heat spikes still need work. The study is an hourly land analysis over multi-decade observations and a high-emissions projection path; it does not replace a monthly ocean mean.[2]
Two instruments for different parts of extreme warmth
Read together, the two reports show why a monthly sea-surface record and an hourly land heat tally answer different questions about extreme warmth. Copernicus gives a single period mean for the ice-free ocean surface in July and places that mean above earlier Julys in the same series, while also noting an El Niño contribution that will turn. Liao and colleagues count hours against a percentile threshold for the same clock hour in a baseline period, then show that a large share of those hours sit on days that never cross a daily hot-day line. That split matters for systems built on daily alerts: heat that arrives in short spikes can remain outside the day-scale label even when the hour itself is extreme. The ocean product does not measure those land hours, and the hourly product does not restate the July sea-surface mean. Side by side they map bulk ocean warmth for one month and the distribution of land heat inside ordinary calendar days. The common subject is extreme warmth measured at mismatched time scales.[1], [2]
