St Kilda, rising starkly from the sea contains the westernmost island of the Outer Hebrides. It is the UK’s only dual UNESCO World Heritage Site, designated for both its natural and cultural significance. Warming land and sea temperatures, more frequent severe storms, and the changes to the ocean currents around St Kilda are the three biggest threats identified by The National Trust for Scotland in their March 2024 Climate Vulnerability Index (CVI) report.
St Kilda is currently a haven to nearly one million seabirds. It is a popular place to spot the UK’s largest Atlantic puffin and the world’s largest of northern gannet colonies. St Kilda is also home to its own unique sub-species of wren and mouse, with the latter being twice the size of a British field mouse. The marine life on the reefs and underwater caves around St Kilda is spectacular.
St Kilda – a very brief history
The final 36 islanders voted to leave St Kilda as life was no longer sustainable and were evacuated in August 1930, ending over 4,000 years of its human habitation. After being used as a nature reserve by the Earl of Dumfries, an expert ornithologist, it was bequeathed to the National Trust for Scotland in 1957 by the 5th Marquess of Bute. Since 1957, the Trust has worked to restore and conserve the island. The Trust provides advice to visitors to help prevent the introduction of non-native, plant, animal, and marine species to its fragile environment. In the past few decades, interest from divers to explore the dense kelp forests surrounding the islands and caves has grown significantly.
St Kilda’s climate vulnerability
64% of people participating in the 2020 People’s Climate vote believe that climate change is a global emergency. To assess St Kilda, the Climate Vulnerability Index (CVI), a rapid and systematic tool developed specifically to assess climate change vulnerability for all types of World Heritage was applied. The CVI has been applied to a diverse range of World Heritage properties around the world.
National Trust for Scotland Property Manager for St Kilda Susan Bain said: “Taking care of St Kilda is a huge task for the National Trust for Scotland. We have certainly been experiencing the effects of climate change on St Kilda for decades, with the impacts on some of the seabird species and marine habitats being particularly profound.” Bain continued, “Warming sea temperatures are already impacting on the food chain for the hundreds of thousands of seabirds who breed here each summer, and some species are at risk of disappearing from St Kilda forever. Changing currents could compound this even further, fundamentally changing the habitats and with that the types of birds that can thrive here.”
In 2023, the National Trust for Scotland counted populations of four species of cliff-nesting seabird on St Kilda, including fulmars with which the island and islanders of the past are so linked. Compared with the previous count in 1999, cliff-nesting seabird numbers had declined by more than half (61%), and fulmars had declined by 70%. The impacts of serial bouts of avian flu continue to take their toll. The Trust has provided advice for advance preparation, hygiene, how to report deaths, and post-visit hygiene advice for those wish to land or dive along the archipelago.
St Kilda represents the fourth CVI application conducted in Scotland’s World Heritage through a partnership between Historic Environment Scotland and James Cook University (Australia). Dr Mairi Davies, Climate Change Policy Manager at Historic Environment Scotland, said: “As part of our initiative to conduct CVI assessments for Scotland’s World Heritage properties, we worked with the National Trust for Scotland and James Cook University to investigate the impact of climate change on St Kilda. The results align with what we are seeing across Scottish heritage properties, which is that climate change and extreme weather are speeding up the deterioration of natural and cultural heritage.”
CVI co-developer, Professor Scott Heron said, “The CVI assessments of Scottish World Heritage, undertaken to date, have indicated moderate to the highest levels of vulnerability to climate threats including from changes in precipitation and temperature. These represent substantial risks from future climate change to the heritage values in each site.”
St Kilda Climate Change Predictions and Recommendations
In addition to the annual temperature rises projected between 1.3 to 5.1° C in summer and 0.6-3.8° C in winter, expanding tourism, infrastructure development and management practices will compound the impact of climate change on St Kilda.
The Trust’s report highlighted that the pressure on the historic environment will affect the preservation of buildings, buried archaeology and pathways across the island. It will also impact wildlife and may include increased sheep mortality as well as reduced feeding and potential starvation of seabirds. There is also the potential for changes in wind pattern and/or direction. Should these occur, they will have a potentially major influence on the environment.
Sea level rises are expected to include further driving storm surges and coastal flooding which impact marine habitats, increase exposure of the islands and exacerbate coastal erosion. Any breakdown of the ocean circulation would likely have substantial consequences on the marine environment. The Atlantic Meridional Overturning Circulation has already been reduced by 15% in recent times and is anticipated to reduce by a further 15% by 2050.
The top recommendations for St Kilda’s adaptation strategy include:
- expanding research into seabird foraging patterns and winter migration,
- expanding the Active Conservation Programme including the management of water courses, upgrading the natural/man-made coastal defences, improving drainage and gutters, and expanding the surveying of cultural landscape,
- expanding the survey of marine areas, and
- expanding the biosecurity plan, and awareness training.
Citizen Participation
Citizen education and participation are vital to ensure that sites like St Kilda are preserved as well as we can. Supporting the National Trust for Scotland and its conservation activities as volunteers can make a huge difference to the properties held in trust to be enjoyed by all. There are many organisations throughout Scotland that can help those who wish to learn more and would welcome volunteers throughout the year. We have listed some of Scotland’s volunteer organisations which include conservation below:
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