So, I was born in India.
This is just a small part
of my big, beautiful family there.
I have, actually, 50,
five zero, first cousins.
Most of us have a couple of kids.
And so all of this leads me
to believe the United Nations
when they tell us that by 2100,
the world will have a population
of almost 11 billion people.
That is, three billion more people
than the planet houses today.
To house all of those people,
we need to build
about 2.4 trillion square feet
of new built space.
Now to give you a sense of scale,
that is the equivalent of adding
to the planet a New York City,
every month ...
for the next 40 years.
Now I'm a New Yorker and an architect,
but this scares even me.
But this is not a scary talk,
I promise you.
(Laughter)
I think I know
what you're probably thinking,
which is, "We are already experiencing
severe impacts from climate change.
How can the world house
another three billion people?
And how can their housing needs
be part of the solution,
rather than part of the problem?"
Could new housing be carbon-negative?
Meaning that it offsets or sequesters
more carbon than it produces.
Now, for our big, existing cities,
there is a lot of hope
in clean energy grids
fueled by renewables like solar,
wind, nuclear and geothermal.
But the fact is, we are still a ways away
from getting fully clean power grids
in our existing cities,
where most of this population growth
is going to occur.
And that's true because of the problems
with everything from transmission lines
to the politics of nuclear energy.
So, clean grids are a really important
part of the solution,
but they don't help us that much,
right at this moment.
What we can do today,
what we have existing technology for,
is to build net-zero single-family homes.
In sunny climates in particular,
solar panels work very, very well,
because it's a lot of roof area,
relative to very few occupants.
But these things,
they're hardly a panacea --
in part because they're very
expensive to build,
but more problematically,
because they induce car-oriented sprawl.
And I don't care if the cars
are electric or autonomous --
sprawl is sprawl,
and it leads to a loss of wetlands,
a loss of forests,
a loss of farms and a loss of community.
So maybe you're thinking the right answer
to house our coming building boom
are towers.
And look, I've actually been called
"Professor Skyscraper."
I love a great tower.
But the reality is we are very far away
from developing carbon-negative towers.
And the reason is,
towers are energy-intensive
to build and operate.
They house a lot of people,
which is great,
but they have very little roof area
to effectively use solar,
and similarly, like,
wind turbines at the top --
all of that stuff barely makes a dent.
On top of that, most skyscrapers
are built out of steel and concrete,
which have a very high degree
of embodied energy.
Now, I hold out a lot of hope
for a technology known
as "mass-timber construction,"
which would allow us to build tall towers
out of environmentally friendly
and fire-retardant wood
that's actually a carbon sink,
but we are a ways away from widespread
adoption of that technology.
I also hold out hope for the idea
that windows could harness solar power,
but the idea that we have
effective and affordable solar glass
in the near future,
that’s even more nascent than mass timber.
So for towers to really be sustainable,
we need those clean energy grids
that we spoke about,
but we don't have them
available to us today.
So we have a paradox.
How do we house all of these people,
how do we build urban
carbon-negative housing
in a means that's technologically
attainable and broadly affordable --
and do that today?
Because I'm tired of talking about 2050.
(Cheers and applause)
I believe that the answer
is hiding in plain sight,
that there is what I call
a “Goldilocks” scale
that sits between the scale
of housing and towers:
two- to three-story housing
that should actually look
very familiar to most of you,
because we built the most beloved
parts of our cities with it.
The row houses of Boston,
the hutong districts of Beijing,
most of the fabric of Edinburgh.
What we now build in this scale
are largely cheap suburban townhomes.
They're banal, they're not sustainable,
they're not walkable,
they're certainly not beautiful.
But could they provide
a hint of a framework
for a human-scale way
of solving this problem
that is great for both the climate
and our societies.
This Goldilocks framework
hits the sweet spot
between the number of people it can house
and the amount of roof area we need
to provide them
and their communities [with] power.
It can be built out of simple
local materials, like wood or brick,
both of which have
relatively low embodied energy
and could be built by local workers.
And the solar panels up above
could be supplemented
with state-of-the-art battery systems
that level out solar supply
and user demand.
Similarly, we can have electric,
state-of-the-art air conditioning
and heating systems --
this exists today.
They can create thermal storage.
What that means is it can produce
ice or hot water off-peak,
for use on-peak.
This housing could compost
food scraps and solid waste,
and turn it into usable soils
or protein for animal feed.
And I think, most importantly,
this kind of housing could provide
affordable, communal, equitable housing
for communities in dire need of it.
And I work with a lot
of these communities,
and I know how much demand
there is for this out there.
Speaking of communities ...
I want to emphasize that this is not
a one-size-fits-all solution.
This is a framework. It's a template.
We can work with communities
to make this housing appealing,
visually and socially,
make it socially and racially mixed,
integrated into the lives
of existing communities.
And when it's built into our cities,
what it means is that it's dense enough
to support mass transit,
like light-rail, express busses, bikes.
There are networks
that plug into jobs, schools, parks
and other daily destinations
in our cities.
This housing is compact enough
that it leaves room for lots of trees
and ground cover.
That means that we can lower
stormwater impacts;
we can reduce the heat island effect;
we can lower the demand
for air conditioning.
And for every family that lives
in an apartment like this,
it's one less house
destroying farms and forests.
Our collaborating engineers at Thornton
Tomasetti have assured us that this is
the lowest-carbon-footprint-per-person
means of habitation,
while also providing a sustainable
use of land on our planet.
I want you to imagine with me
that we deployed this Goldilocks framework
in two places that I love dearly,
New York and Calcutta.
Very different places,
but they have these big,
booming downtowns,
but they also have these growing outskirts
that experience a lot of sprawl.
So they have sites like this
that are near mass transit.
But imagine if, on these sites,
instead of building sprawl,
we built this Goldilocks framework.
Now, that would manifest
in two very, very different ways.
Different materials,
different cultural expressions.
But it would give us carbon-negative,
transit-rich, joyous places
for people to live
and raise their families.
Now, you may be thinking,
"So this is his big idea?
Small-scale housing,
solar panels above, light-rail below,
known technologies throughout,
all organized into these affordable
green neighborhoods?"
Even if you believed me
that this was carbon-negative,
how many of our 11 billion people
could this possibly house?
It's such a modest model.
Well, it turns out,
if all of us lived at this scale,
all 11 billion of us would use up
a landmass equivalent
to the size of France.
Now, I have a feeling that the French
don't want us all invading their country.
(Laughter)
But I make this point
to make a larger point,
which is, we can all live
in this transit-rich,
carbon-negative, affordable way,
and leave the vast majority
of the planet for nature,
for agriculture, for clean oceans.
We can do this.
We know that residential
energy use is so voracious
that this model offsets so much carbon,
it actually more than offsets
all of the cars in the world.
The impact of this would be staggering.
So yes, we can go to 11 --
11 billion people.
We don’t need to fear our neighbors.
We don’t have a lack
of land or technology.
We just have a lack of vision,
because the answers
are hiding in plain sight.
Thank you very much.
(Cheers and applause)