For centuries church organs have created a powerful sense of majesty and mystery, long playing a central role in Britain’s musical and religious heritage.

Now scientists have discovered that they have also inadvertently provided a unique insight into our climate.

Handwritten notes left by generations of organ tuners in some of Britain’s most renowned ancient churches, including many designed by Sir Christopher Wren, have provided a “goldmine” of information.

Monitoring fluctuations in the climate usually relies on data from satellites but researchers have found a much older and more unusual data source in the form of organ-tuning logbooks.

They have provided almost 60 years of data on the temperature and humidity recorded by tuners during their visits to churches to adjust their pipe organs.

Organ tunings usually take place twice a year because the pipes “react to temperature and humidity fluctuations” as the seasons change, according to a study published in the Buildings & Cities journal.

The temperature and humidity can affect the expansion and contraction of the wood and metal. A change of just one degree Celsius can change the pitch of an organ by about 0.8 hertz, making a noticeable difference to the notes produced by the instruments.

Scientists from the school of architecture at Nottingham Trent University accessed 18 logbooks from churches in London, Nottinghamshire and Derbyshire. These included 11 Wren churches and one Nicholas Hawksmoor church, St Mary Woolnoth, in London. The books date back to 1966.

The researchers compared temperatures during the summer months when heating was unlikely to be on. The average indoor temperature across urban churches in the 1966 to 1969 period was 17.2C. By the 2020 to 2024 period the average temperature in summer was 19.7C, a rise of 2.5C. “Initial data analysis reveals a significant conservation risk as the increased and fluctuating indoor temperatures and relative humidity will endanger historic buildings and their artefacts,” the study said.

Andrew Knight of Nottingham Trent University played organs as a teenager.

“I would sit at the organ between hymns,” he said. “Often the only thing to look at between services was this little red book.” His colleague, Yangang Xing, had never heard of them but soon realised they were a “goldmine”, he told The Reengineer newsletter.

The increasing temperatures inside churches may be linked to warming temperatures outside but changes in the use and type of internal heating and ventilation may also play a role.