This is the largest green roof in New York City.
It's in the middle of bustling Manhattan, on top of the Javits Convention Center—
a behemoth of a building with a six-block footprint.
But the roof hasn't always been green.
Before 2014, it was totally barren.
Now, just a few years later, when people walk out onto the roof, they say things like:
"Amazing," "That's great," "I didn't expect this," "What a surprise."
But besides the great reactions, there are practical benefits.
We have 300,000 bees.
We've seen 25 different species of birds on the roof.
We reduced the temperature up here by about six degrees Fahrenheit.
And we also save about 7 million gallons of stormwater runoff
that's absorbed in the soil and the plants that are on our roof.
We've been able to reduce our energy
consumption by about 26 percent,
and that translated for us last year
into a saving of about 3 million dollars.
That is impressive.
How does one green roof get so much done?
And what are all of the NOT green roofs in New York City doing with their lives?
First, let's see how much roof space actually exists.
You know, they are a major part of urban landscapes.
The the round number that most of us think exists is about 1 billion square feet.
One billion with a 'b.'
That's like 22 times the size of Central Park, in roofs.
And in most cities, what isn't roof is another impermeable surface
like road, sidewalk, or parking
lot.
And these surfaces create a lot of problems for cities
That green roofs can actually help solve.
Let's take a look at three of these issues. The first is
stormwater runoff.
Rainwater goes in pipes. It combines
with what's called sanitary water.
When there's too much rainwater, which happens hundreds of times a year around Manhattan,
the wastewater treatment
systems shut down, and valves just let
the water just,  you know, shunt out into the rivers. You know, it's got human sewage.
It's the biggest source of pathogens to
the Manhattan Island.
With green roofs, that water instead of going into the
drain and polluting the environment,
ends up just evaporating the atmosphere
through the leaves of these plants.
And then, there's what scientists call the "heat island effect,"
which basically means that cities are significantly warmer than the surrounding areas.
I've seen asphalt roofs get up easily 170, 180 degrees Fahrenheit in the strong sunlight.
They absorb about 90 to 95 percent of the sunlight.
Green roofs, by comparison are close to air temperatures.
Another problem green roofs can help solve is habitat loss.
Cities can shrink or destroy the green space that's crucial for certain plants and
animals to survive.
Currently a lot of species might occur in  smaller parks throughout the city that are relatively unconnected,
But having high densities of green roofs would allow those patches to be more connected.
Letting, for example, butterflies travel from patch to patch with lots of stepping stones of green roofs in between.
And these are just three of the problems that green roofs can help solve.
But to really put a dent in any of these issues
cities would have to implement green roofs at a large scale.
Stuart Gaffin, the research scientist
you heard from earlier,
estimates that if all of New York City's 1 billion square feet of roof space were greened,
those green roofs could lower the city's
temperature by nearly two degrees Fahrenheit
and absorb over 10 billion
gallons of stormwater each year.
As cities continue to grow, all that empty roof space starts to look more and more like an opportunity,
an untapped resource,
a future ecosystem of problem-solving meadows
in the sky.
