How quickly temperatures rise isn’t just about how warm the air starts out, but how dry the land and atmosphere are.
Dry ground heats up faster than moist ground because less energy is used for evaporation and more goes directly into raising temperature.
There is strong evidence that UK summer soils are becoming drier as the climate warms, with Met Office projections showing earlier seasonal drying and more frequent droughts, particularly in southern and eastern England.
The same principle applies higher above the ground. Large, slow‑moving areas of high pressure – often called blocking highs or heatdomes – are large areas of sinking air.
Like squeezing a sponge, the descending motion dries the air out and when you add in the fact the air is compressed, this also adds to the air heating up.
While blocking highs may not be happening more often, studies suggest that when they do occur the heat and dryness they bring are more intense than in the past.
As Professor Sarah Perkins‑Kirkpatrick, climate scientist from the Australian National University puts it: “The dice are loaded for it to be hotter more quickly…as soon as high pressure systems move over, bang, the temperature goes up.”