Climate changes are affecting the timings of natural processes with many key biological events in the UK - such as leaf out and flowering - now taking place earlier (and some autumn events also later) in the year when compared with historical records.
The latest edition of the State of the UK Climate report [published on Monday 14 July 2025] showed the flowering of hazel trees has advanced significantly over the period from 1999-2024. Looking at the information collated by the Woodland Trust from data submitted to the Nature’s Calendar survey by thousands of citizen scientists across the UK revealed the flowering of hazel was almost ten days (9.7) earlier in 2024 than the average for the period from 1999 to the present day.
Prof Tim Sparks is one of the UK’s leading scientists studying phenology – the study of the timing of natural events in relation to climate. He said: “The natural world is responding to the changes we are witnessing within our own climate.
“A wide-ranging study published in 2022 showed an alarming discovery. Comparing two periods from 1753 to 1986 and 1987 to 2019 researchers found that flowering dates are a full month earlier in the UK than compared with the previous period. This can create an ecological misfit for other species relying on the flowering and annual development of plants.”
The Met Office #StateOfUKClimate Report for 2024 demonstrates how weather records and temperature and rainfall extremes are becoming increasingly frequent in the UK
— Met Office (@metoffice) July 14, 2025
Scroll through some key findings from the report ➡️
Learn more: https://t.co/lWe06Ulw1q
2024 saw the earliest frogspawn and nesting blackbird since 1999, although the effect on other species, such as the speckled wood butterfly, was less noticeable.
Judith Garforth is the Woodland Trust’s Citizen Science Office for Nature’s Calendar. She said: “A change in the timing of seasonal events is one of the first and most noticeable responses of nature to weather and climate. It’s an early warning to the changes in species abundance and range that may follow.
“Some species may benefit from an early spring. An early start to blackbird nesting in spring 2024 may have allowed for more broods in that year, however raising of the chicks will only have been successful if the worms and caterpillars required to feed the young were also available early.
“Early laying of frogspawn is perhaps a riskier strategy because subsequent cold snaps can hinder frogspawn survival. Phenology records from the Nature’s Calendar project are often used by scientists investigating these complex species interactions to understand what the knock-on effects of seasonal change will be.”
Phenology in the UK has records from 1736 when Robert Marsham began recording 27 ‘indications of Spring’ on his Norfolk estate until his death in 1797. The valuable record was continued by his family until 1958.
READ MORE: How is Summer 2025 shaping up so far?
A national phenology network began in 1875 when the (Royal) Meteorological Society launched a program - which included recording flowering dates of up to 13 plant species and the appearance of specific bird and insect species. This ran until until 1948.
The UK Phenology Network was resurrected in 1998 by the Centre for Ecology and Hydrology by Professor Tim Sparks. In 2000 the Woodland Trust took responsibility to promote phenology to a wider and larger audience. The resulting Nature’s Calendar initiative - which collects phenology records in all seasons - has around 4000 active participants with a database approaching three million records.
Judith Garforth added: “With a changing climate it is vital to continue collecting phenological records. The gap between 1948 and 1999 when we had no UK phenology recording scheme coincides with a big change in mean spring temperature.”