High above the beaches of north Cornwall, the rocky cliffs at Godrevy quietly hold secrets about Earth’s ancient climate. These cliffs, carved and shaped by waves more than 100,000 years ago, show where the shoreline once stood several metres higher than today. Similar raised beaches can be found along other parts of Cornwall’s coast, including Bream Cove near Falmouth and Porth Nanven near Land’s End.
These old shorelines tell an important story about the planet’s past. During warm periods like the one more than 100,000 years ago, huge ice sheets in Greenland and Antarctica melted, pouring water into the oceans and raising sea levels around the globe. But figuring out exactly which ice sheets melted and how much remains a mystery that scientists are racing to solve.
When ice forms on land in giant sheets, its mass actually pulls ocean water towards it, making nearby sea levels higher. As this ice melts and shrinks, that gravitational pull weakens, and sea levels close to the ice sheet can fall rather than rise. For example, as Greenland’s ice retreats today, sea levels along its nearby coasts are dropping, not rising. The opposite effect sea level rise happens farther away, like in Scotland.
This unique “fingerprint” of ice melt can help researchers figure out where the melting happened in the past by studying ancient beaches and coral reefs worldwide. The raised beaches in Cornwall suggest that much of the meltwater long ago came from Antarctica, though hard evidence for this has been difficult to find.
To settle the mystery, an international team of scientists including researchers from the UK is preparing to drill deep beneath Antarctica’s Ross Ice Shelf. Starting later this year, the team will travel to a remote site using snow vehicles and drill through 500 metres of ice to collect sediment from the seafloor below. These sediment cores could reveal when and how Antarctica’s ice sheets melted in the past.
These clues from deep beneath the ice are vital. As the world rapidly warms due to rising carbon dioxide levels, the future of the Antarctic ice sheet could decide how high sea levels will rise threatening coasts around the globe. Today, atmospheric carbon dioxide levels are as high as they were more than 3 million years ago during the mid-Pliocene, a period when sea levels were much higher than today.
Communities in Cornwall are already thinking about this future. In the town of Bude, residents have formed a “climate jury” to help decide how to manage the risks of sea level rise. This local approach to climate planning could become a model for other towns facing the same challenge.
The ancient beaches above Cornwall’s coast are reminders that sea levels have been much higher before and that they could rise again if Antarctic ice sheets retreat in the years to come. What scientists find beneath the Ross Ice Shelf may help predict how serious that risk is.