As World Ocean Day approaches (8 June), thalassophile Jonathan White talks to us about his new book Tides: the Science and Spirit of the Ocean and the Bristol Channel

TBM: In your new book you document your travels all over the world to learn everything you can about tides. What prompted you to undertake such a massive journey?
J: I grew up on the California coast, surfing and sailing. I always had a tide chart in my back pocket. I knew the moon had something to do with the tide, but that was it. After almost losing my boat in a large Alaskan tide, I wanted to learn more about this great mystery. I thought I’d read a book or two, but two books turned into 10, then 300. The subject of tides was far more complex and fascinating and poetic than I imagined. My search took me across the globe in search of the fastest, largest, and scariest tides on the planet.

The Severn Estuary has been at the centre of discussions about renewable energy for years now. Is tidal power really a viable source of sustainable energy for the future?
Tidal energy is clean, dependable and plentiful. It may not be the silver bullet for future energy needs, but it will definitely play an important and lasting role, along with solar, wind, wave, and geothermal. There are many worthy tide-energy projects underway right now, not just here in the UK but in Maine, New York, the Bay of Fundy, Alaska, British Columbia, Australia, Russia, China, Japan, and New Zealand. Scotland, with its large testing site in the Orkney Islands, is a world leader in experimentation. Chile, on the other hand, is just beginning, but they have tremendous tide resources to tap.

The Bristol Channel has an extraordinarily large tide – over 12 meters at times – and a tidal bore (on the Severn) as well. The Channel is a unique confluence of population, industry and ecological wealth. As you know, it’s the largest estuary in the UK. The Swansea tidal project here in the Bristol Channel is promising, with a goal of supplying energy to 120,000 homes.

Not everyone knows that tide mills have been harnessing energy for hundreds of years. The earliest may have been in operation at river mouths during Roman times, 1600 years ago. During their heyday, in the 17th century, thousands of tide mills across Europe and the U.S. east coast were grinding cereals, stamping copper, sawing wood, pumping brine for salt and crushing pulp for paper.

What was the most interesting place you visited on your journey and why?
I enjoyed all the places I visited, with highlights being Mont St-Michel in France, the San Blas Islands off Panama, the Bay of Fundy in eastern Canada, and the Orkney Islands. That said, perhaps the most unusual experience was slipping under the Arctic ice with Lukasi Nappaaluk, an Inuit elder. I joined him in Kangiqsujuaq, his small village in eastern Canada, just south of the Arctic Circle. On an exceptionally low winter tide, Lukasi chopped a hole in the three-foot-thick ice and disappeared into the dark womb-like cavities below. I followed. It was scary, but the other-worldliness of those couple hours under the ice, gathering mussels and eyeing the rising tide as it started to re-fill our womb, is still haunting.

Did you ever run into any danger on your expeditions?
I was searching for the most extreme tides in the world, which naturally – and often – put me in danger. In China, I waited in the river flats of the Qiantang so I could encounter the Silver Dragon, a tidal bore that reaches eight meters and has wrought unimaginable destruction over the last 2,500 years. In California, I bobbed in the line-up at Maverick’s while watching the big wave surf contest. And on Canada’s British Columbia coast, I took my skiff into the 18-knot currents at Skookumchuck, a First Nations word meaning ‘Fast Water’.

How is climate change affecting tides, and what changes can we expect to see in coastal areas like the South West (UK) in the future?
Technically, tides are a periodic change in sea level attributed to an astronomical force (like the sun and moon). But scientists agree that the tides are influenced by hundreds of other factors, such as weather, seismic activity, wind, resonance and long-term cycles of planetary heating and cooling. We’re accustomed to seeing the tides come and go on a daily time-scale, but if we broaden our perspective we’d see the tides rising and falling over much longer time-scales. 20,000 years ago, for example, the earth was at the peak of a glaciation period, and during that time much of the ocean’s water was locked up in ice. The tide was out, so to speak: sea level was so much lower than it is today, and has been rising ever since. The heating of the earth by the last couple hundred years of fossil fuel burning has hastened this rising tide.

Changing sea levels will affect the tide, but it’s hard to predict exactly how much and where. As the shape of our coast changes, some areas will see larger tides and some areas will see smaller tides. Even the defences against these rising seas will change over time, depending on economics, geography, technology, and the urgency of the threat. In Venice, they’re building ‘gates’ at the three entrances to the Venice Lagoon. The Thames Barrier, built in the 1980s, protects London, and there are similar defense systems in Denmark and Russia. Bangladesh, the Maldives, the San Blas Islands and some of the South Pacific islands don’t have the finances or the geography to defend themselves with gates or barriers. They will have to move. Soon.

You’re about to start your UK book tour – where can we hear you speak?
I’m thrilled to be speaking at the wonderful Bristol Natural History Consortium’s Festival of Nature on Monday 4 June at ‘The Station’. The talk starts at 6.30pm and tickets are £4.