You may have noticed that every year the leaves turn yellow and fall later and later. You didn't: a review of 64 studies from 1931 to 2010 in Asia, Europe and North America confirmed that rising global temperatures have delayed leaf fall in the Northern Hemisphere. Michael Lavelle, a senior lecturer in the Department of Landscape Management at Anglia Ruskin University, examined the causes and consequences of this trend in the pages of The Conversation.

The mechanisms of the end of a plant's growing season are complex but well understood. Deciduous trees go into winter in three stages. In the first, the plant hormone auxin plays a leading role. It is produced in growing tissue and suppresses bud growth further down the branch. As day length shortens and the daily temperature drops, abscisic acid is produced. Throughout the fall, both of these substances accumulate in the plant - and eventually stop cell division and expansion in the resting buds.

By mid-fall, the tree is no longer growing, but it can still be clothed in foliage if conditions remain mild. This gives it a chance to absorb leftover nutrients from the leaves, which is what causes the leaves to change color. Eventually, the branch forms protective plugs at the base of each leaf, causing it to fall off.

Climate change has disrupted the usual pattern of changing seasons. In 2022, trees that normally bloom in the spring bloomed in the fall. This was due to an unusual summer, which was Britain's hottest and fifth driest since 1890.

By August, the leaves had already turned brown and fallen off. The heat and drought slowed growth and caused abscisic acid levels to spike. Fruit also came early: blackberries, which usually don't produce until August, started fruiting as early as June 28. It seemed as if fall had arrived at the height of summer.

It was a meteorological autumn. It was the third warmest since 1884 and the 13th wettest since 1836. Plants began to bud and bloom, mistaking it for spring. The “false spring” came to an end, replaced by a rather harsh winter. This was a devastating blow to the trees - at Anglia Ruskin University's Writtle campus, about 30% of the plants, including those considered hardy, died.