In leafy South Kensington there is a 3,000 sq m artificial ocean in a basement. I kid you not. Dave de Ruyter has been managing the Hydrodynamics Laboratory at Imperial College for nearly 20 years. His enthusiasm remains undimmed. “Look at that,” he says, pulling open a hatch in the floor to reveal water running below our feet. “Not many places have this! When it’s full, the system contains 1.2 million litres of water.” The pumps and sump supply two large wave basins and six flumes that can recreate everything from deep-water swells to currents and wind-driven seas.

Under the watchful eye of PhD student Oliver Millar, we begin with a neat wave. “This is a very nice mathematical wave,” he says approvingly. Then he begins to move some of the 56 paddles. The surface becomes restless, the pattern changes. As the waves build, he raises his voice above the clanking and sloshing. “OK, this is really a very good representation of a North Sea storm at a scale of one to 100. In real life the largest waves here would be around 10 metres.” By shrinking a storm, researchers can safely recreate extreme conditions, measure exactly how waves behave and scale the results back up.

But a very real extreme weather-maker is brewing thousands of miles away. The developing El Niño — a mass of unusually warm water across the tropical Pacific with the power to shift weather patterns around the planet — could be one of the strongest on record. It has even earned the nickname “Godzilla”. The Met Office says it increases the chances of wetter, stormier conditions across the UK and north-west Europe this autumn and winter.

El Niño is the term for when sea surface temperatures in the central and eastern tropical Pacific rise above average, disrupting normal wind patterns and shifting rainfall around the world.

The climate is already wetter. Research shows the extra rain now falling across the UK each winter as a result of fossil-fuel-driven global warming would fill three million Olympic swimming pools. London is particularly exposed, facing flood risk from three directions: North Sea storm surges pushing up the tidal Thames; swollen rivers and tributaries; and intense rainfall overwhelming the drainage of a densely built city.

Read More: A Godzilla El Niño is coming — and London is on the front line