Every year people ask me, “why haven’t the leaves fallen yet?” If autumn starts on September 1 then by early November winter should be well on its way. And yet, an amateur photographer who has captured the season’s colours for several years in southern England recently told the BBC that 2024 appears to be running behind schedule.
You may have noticed it too: it is becoming more common for leaves to drop later in the season. A 2015 review of 64 studies, with observations ranging from 1931 to 2010 across Asia, Europe and North America, found that rising global temperatures had delayed leaves falling in the northern hemisphere.
To understand what is happening, we need to remember that trees perceive the world differently to us. They follow a combination of environmental cues to time the shedding of their leaves. Foliage tends to fall gradually, starting in October and sometimes taking until early December. Most trees native to the UK hold onto their leaves until it gets cold, which usually happens by November. In essence, it either gets too cold, or too dark, and eventually, the plant becomes fully dormant.
