Every week, a whopping three million new people are moving to live in a city. That’s equivalent to the current population of San Diego or Kiev transplanting themselves into urban areas every seven days; it’s almost a new Moscow or Rio de Janeiro every month.

By 2030, 60% of the world’s population will be living in cities. This is going to put huge strain on the world’s existing metropolises. And they will have climate change to deal with too ­– about 90% of the world’s largest cities are situated on the waterfront and are vulnerable to rising sea levels.

To cope with these changes, some engineers, researchers and technologists say we should reconsider how we build cities; that perhaps it’s time to do something totally different. Instead of building on land, they say, let’s make them float on the ocean.

But is this idea actually feasible? What might these cities look like in reality, and how would they work?

As you can hear in the preview below, these were questions that we explored for a recent episode of the BBC Tomorrow’s World podcast. Along with my fellow presenter Britt Wray, we spoke to designers who are proposing floating cities that could change with the seasons, tech entrepreneurs looking to create settlements on the open ocean and marine engineers who are putting these ideas to the test. Here’s what we found out.