In early September, a season when summer's grip is expected to loosen, North African heat has surged across the Iberian Peninsula and into the broader Mediterranean world, pushing Spain to temperatures that belong to the height of midsummer. The event speaks to a deepening pattern in which the boundaries of extreme heat stretch further in time as well as geography. Britain will feel a brief, tempered echo of this warmth over the weekend before the Atlantic reasserts its cooler, wetter character — a reminder that proximity to extremes does not always mean sharing in them.