This time, I'm going to talk about future cities.

A modern city can be thought of as gigantic creature

that depends on resources fed to it from around the planet.

However, in the future,

such global supplies cannot be guaranteed.

Cities have evolved into sophisticated cybernetic machines

for keeping civilization alive.

In some aspects, cities are therefore humanity's greatest achievement.

Nevertheless, most cities would decend into anarchy

in only 48 hours without a constant supply

or food, energy and clean water.

The Industrial Revolution saw a mass migration

of people from the country side.

Those who remained on the land

then had to develop increasingly intensive farming methods

to meet the food requirements of urban dwellers

who could not feed themselves.

Canals, railways and roads allowed the first industrial cities

to be supplied with their daily nutrition.

However, this resulted in a food chain

dependant not just on the complex transport infrastruture,

but also fuel and modern fertilizers.

As a consequence, today, every calorie we eat

also requires the consumption of 10 calories of oil.

And within a few decades at best,

this addiction of the modern city to petroleum

will no longer be sustainable.

There are, however, possibilities that the farm

may migrate from the countryside.

So called 'vertical farming' could involve multi-tiered city farms

in future glass skyscrapers or pyramids.

Such stacks of artificial fields would allow city dwellers

to harvest crops all year round in areas without available land.

They would also significantly reduce

the energy required for food transportation,

would lower crop loss associated with shipping and storage,

could recycle their own water,

and, within their sealed environments,

may even use fewer pesticides.

One vertical farm could potentially feed 50,000 people.

However, even before the construction of such massive projects,

laws could be passed requiring all new buildings in large cities

to have at least some space dedicated to food production.

For example, new apartment blocks could be required to include

hydroponical lodgements on the roof.

In addition to food, all cities currenly require significant natural resources

to meet their raw energy needs.

However, alternative technologies,

including solar cells, rooftop wind turbines,

ground source heat pumps,

and methane power plants fuelled from domestic rubbish

could see future cities becoming at least partly energy sufficient.

Micro power generation may even extend to piezo-electric paving slabs

to generate electricity from our footsteps,

as well as hydraulic plates in road surfaces

that would generate power as vehicles drive over them.

In addition to producing at least some of their own food and power,

future cities will also have to use fresh water far more efficiently.

In part this is because treating and transporting fresh water is energy intensive.

However, half of the world's population now live in countries

where the water table is falling.

Future cities will therefore need to capture

and recycle water whenever this is possible.

Future food, energy and water supplies are at best uncertain.

The global population of city dwellers also continues to increase.

Future cities will there have to become leaner and more self-sufficient.

For more information, please see ExplainingTheFuture.com.

But now that's it for another video.

And remember, the future is in your hands.