The event, which was set to take place on Wednesday at the Shaw Library

The event venue, like most buildings in London, does not have any cooling mechanisms in place,

I think that every library I've ever been in in the US has been climate controlled. I suspect that it's not just for the comfort of patrons, but that it probably preserves books.

searches

https://conserv.io/blog/book-storage-humidity/

According to the Northeast Document Conservation Center (NEDCC), optimal relative humidity (RH) levels for paper materials lie somewhere between 30% and 50% with a certain preference for the lower end to slow down deterioration reactions. (NEDCC, 2018)

The Library of Congress, for example, suggests about 35% RH for works on paper. However, this low RH may not be suitable for all books in your collection. For example, leather-bound books may require higher humidity levels to maintain their flexibility and avoid cracking or tearing (CCI, 2018).

High humidity levels can create an ideal environment for mold growth and pest infestations. Mold thrives in humid conditions (65% and above), and if left unchecked, can cause permanent damage to your collection, including staining, weakening, and even disintegration of materials (Conserv o Gram, National Park Service, 2007). Additionally, many pests, such as silverfish and booklice, are attracted to warm, damp environments and may cause further mechanical harm to your books as they graze over the surfaces (AIC Wiki).

https://weather-and-climate.com/average-monthly-Humidity-perc,London,United-Kingdom

London's humidity levels vary throughout the year. The highest levels occur in November, reaching 81% (very high), while the lowest is recorded in April at 64%.

Throughout the year, the average humidity in London is 72%.