If we get our cities right,

we just might survive the 21st century.

We get them wrong,

and we're done for.

Cities are the most extraordinary experiment in social engineering

that we humans have ever come up with.

If you live in a city,

and even if you live in a slum --

which 20 percent of the world's urban population does --

you're likely to be healthier, wealthier, better educated

and live longer than your country cousins.

There's a reason why three million people are moving to cities

every single week.

Cities are where the future happens first.

They're open, they're creative, they're dynamic, they're democratic,

they're cosmopolitan,

they're sexy.

They're the perfect antidote to reactionary nationalism.

But cities have a dark side.

They take up just three percent of the world's surface area,

but they account for more than 75 percent of our energy consumption,

and they emit 80 percent of our greenhouse gases.

There are hundreds of thousands of people who die in our cities

every single year from violence,

and millions more who are killed as a result of car accidents

and pollution.

In Brazil, where I live,

we've got 25 of the 50 most homicidal cities on the planet.

And a quarter of our cities have chronic water shortages --

and this, in a country with 20 percent of the known water reserves.

So cities are dual-edged.

Part of the problem is that,

apart from a handful of megacities in the West and the Far East,

we don't know that much about the thousands of cities

in Africa, in Latin America, in Asia,

where 90 percent of all future population growth is set to take place.

So why this knowledge gap?

Well, part of the problem

is that we still see the world through the lens of nation-states.

We're still locked in a 17th-century paradigm

of parochial national sovereignty.

And yet, in the 1600's,

when nation-states were really coming into their own,

less than one percent of the world's population

resided in a city.

Today, it's 54 percent.

And by 2050, it will be closer to 70 percent.

So the world has changed.

We have these 193 nation-states,

but we have easily as many cities that are beginning to rival them

in power and influence.

Just look at New York.

The Big Apple has 8.5 million people

and an annual budget of 80 billion dollars.

Its GDP is 1.5 trillion,

which puts it higher than Argentina and Australia,

Nigeria and South Africa.

Its roughly 40,000 police officers

means it has one of the largest police departments in the world,

rivaling all but the largest nation-states.

But cities like New York

or São Paulo

or Johannesburg

or Dhaka

or Shanghai --

they're punching above their weight economically,

but below their weight politically.

And that's going to have to change.

Cities are going to have to find their political voice

if we want to change things.

Now, I want to talk to you a little bit about the risks

that cities are facing --

some of the big mega-risks.

I'm also going to talk to you briefly about some of the solutions.

I'm going to do this using a big data visualization

that was developed with Carnegie Mellon's CREATE Lab and my institute,

along with many, many others.

I want you to first imagine the world not as made up of nation-states,

but as made up of cities.

What you see here is every single city

with a population of a quarter million people or more.

Now, without going into technical detail,

the redder the circle, the more fragile that city is,

and the bluer the circle, the more resilient.

Fragility occurs when the social contract comes unstuck.

And what we tend to see is a convergence of multiple kinds of risks:

income inequality,

poverty,

youth unemployment,

different issues around violence,

even exposure to droughts, cyclones and earthquakes.

Now obviously, some cities are more fragile than others.

The good news, if there is any,

is that fragility is not a permanent condition.

Some cities that were once the most fragile cities in the world,

like Bogotá in Colombia

or Ciudad Juárez in Mexico,

have now fallen more around the national average.

The bad news is that fragility is deepening,

especially in those parts of the world that are most vulnerable,

in North Africa, the Middle East,

in South Asia and Central Asia.

There, we're seeing fragility rising way beyond scales we've ever seen before.

When cities become too fragile they can collapse,

tip over and fail.

And when that happens,

we have explosive forms of migration:

refugees.

There are more than 22 million refugees in the world today,

more than at any other time since the second world war.

Now, there's not one refugee crisis;

there are multiple refugee crises.

And contrary to what you might read in the news,

the vast majority of refugees aren't fleeing from poor countries

to wealthy countries,

they're moving from poor cities into even poorer cities --

often, cities nearby.

Every single dot on this map represents an agonizing story

of struggle and survival.

But I want to briefly tell you about what's not on that map,

and that's internal displacement.

There are more than 36 million people who have been internally displaced

around the world.

These are people living in refugee-like conditions,

but lacking the equivalent international protection and assistance.

And to understand their plight,

I want to zoom in briefly on Syria.

Syria suffered one of the worst droughts in its history between 2007 and 2010.

More than 75 percent of its agriculture and 85 percent of its livestock

were wiped out.

And in the process, over a million people moved into cities

like Aleppo, Damascus and Homs.

As food prices began to rise,

you also had equivalent levels of social unrest.

And when the regime of President Assad began cracking down,

you had an explosion of refugees.

You also had over six million internally displaced people,

many of whom when on to become refugees.

And they didn't just move to neighboring countries like Jordan

or Lebanon or Turkey.

They also moved up north towards Western Europe.

See, over 1.4 million Syrians made the perilous journey

through the Mediterranean and up through Turkey

to find their way into two countries, primarily:

Germany and Sweden.

Now, climate change --

not just drought, but also sea level rise,

is probably one of the most severe existential threats

that cities face.

That's because two-thirds of the world's cities are coastal.

Over 1.5 billion people live in low-lying, flood-prone coastal areas.

What you see here is a map that shows sea level rise

in relation to changes in temperature.

Climate scientists predict that we're going to see

anywhere between three and 30 feet of sea level rise

this side of the century.

And it's not just low island nation-states that are going to suffer --

Kiribati or the Maldives or the Solomons or Sri Lanka --

and they will suffer,

but also massive cities like Dhaka,

like Hong Kong,

like Shanghai.

Cities of 10, 20, 30 million people or more

are literally going to be wiped off the face of this earth.

They're going to have to adapt, or they're going to die.

I want to take you also all the way over to the West,

because this isn't just a problem in Asia or Africa or Latin America,

this is a problem also in the West.

This is Miami.

Many of you know Miami is one of the wealthiest cities

in the United States;

it's also one of the most flood-prone.

That's been made painfully evident by natural disasters throughout 2017.

But Miami is built on porous limestone -- a swamp.

There's no way any kind of flood barrier

is going to keep the water from seeping in.

As we scroll back,

and we look across the Caribbean and along the Gulf,

we begin to realize

that those cities that have suffered worst from natural crises --

Port-au-Prince, New Orleans, Houston --

as severe and as awful as those situations have been,

they're a dress rehearsal for what's to come.

No city is an island.

Every city is connected to its rural hinterland

in complex ways --

often, in relation to the production of food.

I want to take you to the northern part of the Amazon, in Rondônia.

This is one of the world's largest terrestrial carbon sinks,

processing millions of carbon every single year.

What you see here is a single road over a 30-year period.

On either side you see land being cleared for pasture, for cattle,

but also for soy and sugar production.

You're seeing deforestation on a massive scale.

The red area here implies a net loss of forest over the last 14 years.

The blue, if you could see it -- there's not much --

implies there's been an incremental gain.

Now, as grim and gloomy as the situation is -- and it is --

there is a little bit of hope.

See, the Brazilian government,

from the national to the state to the municipal level,

has also introduced a whole range -- a lattice -- of parks and protected areas.

And while not perfect, and not always limiting encroachment,

they have served to tamp back deforestation.

The same applies not just in Brazil but all across the Americas,

into the United States, Canada and around the world.

So let's talk about solutions.

Despite climate denial at the highest levels,

cities are taking action.

You know, when the US pulled out of the Paris Climate Agreement,

hundreds of cities in the United States and thousands more around the world

doubled down on their climate commitments.

(Applause)

And when the White House cracked down on so-called "undocumented migrants"

in sanctuary cities,

hundreds of cities and counties and states sat up in defiance

and refused to enact that order.

(Applause)

So cities are and can take action.

But we're going to need to see a lot more of it,

especially in the global south.

You see, parts of Africa and Latin America are urbanizing

before they industrialize.

They're growing at three times the global average

in terms their population.

And this is putting enormous strain on infrastructure and services.

Now, there is a golden opportunity.

It's a small opportunity but a golden one: in the next 10 to 20 years,

to really start designing in principles of resilience into our cities.

There's not one single way of doing this,

but there are a number of ways that are emerging.

And I've spoken with hundreds of urban planners,

development specialists,

architects and civic activists,

and a number of recurring principles keep coming out.

I just want to pass on six.

First: cities need a plan

and a strategy to implement it.

I mean, it sounds crazy,

but the vast majority of world cities don't actually have a plan

or a vision.

They're too busy putting out daily fires to think ahead strategically.

I mean, every city wants to be creative,

happy, liveable, resilient --