Are heatwaves evidence that climate change is speeding up?

Estimates of Earth’s average temperature, having set a new record on July 3rd, have yet to fall back below the previous record, which was set just last year. That a should happen in July is, by itself, perhaps unsurprising. Two-thirds of the Earth’s land is in the northern hemisphere, and land warms up faster than water does, so northern summers are the hottest times of year for the planet as a whole. But the highest temperatures tend to come later in the season. That this year’s should start so early, rise so high and run so long is unprecedented.So is what is happening in the oceans (see chart). Since March 13th the sea-surface temperature in low- and mid-latitudes has been higher than on the same day in any year since 1979. Normally highest in the southern summer (most of Earth’s water is in the south), temperatures are at record levels in the southern winter.