and the glaciers that for now, at least, dot the globe. Their common color, white,
helps keep them all from heating up. Of all the colors, white absorbs the least amount of heat.
It's color that Purdue University mechanical engineering professor
Xiulin Ruan thought could help with climate change. Ruan and several of his students
spent years on a quest to invent a new kind of white paint that could cool the planet.
XIULIN RUAN, Purdue University: You only need to paint less than 1 percent of the Earth's surface,
no matter is it roofs, roads, cars. We should be able to totally reverse global
warming and bring the temperature back to where we want it to be.
JOHN YANG: Commercial white paint is widely used in hotter climates because it reflects
80 to 90 percent of sunlight, which keeps surfaces from getting too hot. But Ruan
wanted to take it a step further and figure out something that would actually cool surfaces.
XIULIN RUAN: So, what our paint does, it reflects as high as a 98.1 percent of sunlight, which means
it only absorbs 1.9 percent of sunlight, almost no heat from the sun.
Commercial white paints, they still absorb 10 to 20 percent. So, in essence,
we cut the heat going from the sun by five to 10 times. That's a big deal.
JOHN YANG: And that's enough to make the difference between something that
cools itself and something that heats up?
XIULIN RUAN: Yes, exactly.
JOHN YANG: One of Ruan's students, Ph.D. candidate Joe Peoples,
showed us what makes this paint different. It contains high concentrations of the chemical
compound barium sulfate, which is used in cosmetics and to brighten photographic paper.
JOE PEOPLES, Purdue University: Many people think this is very
dangerous. It's actually not. It's actually safe to ingest.
So, when you do medical X-rays of your bowels, you actually take barium
sulfate. It makes your bowels opaque, so that you can see them in the X-ray.
JOHN YANG: And how much paint are you going to make now?
JOE PEOPLES: This will make about 50 to 100 milliliters of paint. It takes
around 18 hours. And that will cover around a three-by-three-inch square.
JOHN YANG: To see one of those small,
painstakingly painted copper squares in action, we went up to the rooftop.
JOE PEOPLES: This tile here is actually the brightest commercial white paint we
can get. It has the most reflectivity of around 88 percent. And then this is
our barium sulfate paint, which has a reflectivity of around 98.1 percent.
JOHN YANG: And just with the naked eye, this looks a brighter white than this.
JOE PEOPLES: Correct.
JOHN YANG: And, actually, this is cool to the touch.
JOE PEOPLES: Already, yes. This one is absorbing so much more solar energy. Therefore,
it's heating up, while this one is absorbing a little amount of solar energy, but it's
rejecting more to deep space. So, therefore, we're getting it below ambient temperatures.
JOHN YANG: So, it's actually cooling?
JOE PEOPLES: It's actually cooling. Just sitting here by itself with no electricity,
it's cooling down below this outdoor temperature we feel now.
Wow, they're about 10 degrees different right now.
JOHN YANG: To give us an idea of the difference the paint makes,
Ruan and Peoples fired up an infrared thermometer.
JOE PEOPLES: What you can see here is, this square is very orange, right...
JOHN YANG: Right.
JOE PEOPLES: ... which means it's very warm compared to our paint, which is a nice dark
color, which means it's much, much cooler.
JOHN YANG: On this sunny 73-degree Fahrenheit day,
the tile with their white paint was nearly 15 degrees cooler than the one
with commercial paint and more than two degrees cooler than the surrounding air.
We were on top of the world's largest air conditioning research lab,
something Ruan and Peoples hope the world will need less of with their paint.
Could this really could eliminate the need for air conditioning?
XIULIN RUAN: I mean, you could eliminate air conditioning for certain sort of locations, and
I would say a certain time of the year. If you use this in Phoenix, Arizona, or Reno,
Nevada, it could save up to 75 percent of the cooling during the summer months.
JOHN YANG: Large-scale production would mean increased mining for barite,
but Ruan says their paint is more environmentally friendly than current commercial white paint.
It took the researchers more than seven years to test over 100 different materials,
before landing on this winning formula.
Tell me what it was like that moment or that day you realized you had succeeded,
that this was actually cooling below ambient temperature?
JOE PEOPLES: As you can imagine, my Ph.D. research was literally watching paint dry.
(LAUGHTER)
JOE PEOPLES: So, when we actually finally got something that was successful and
what we had theorized for so many years, it was extremely validating.
XIULIN RUAN: And I start to realize -- when we got so much interest from people all over the globe,
we came to realize that many people need cooling in an affordable way.
And many places, aside from cooling, we need to address climate change.
Our work can have a far-reaching impact than we thought.
JOHN YANG: They have applied for a patent for the formula and partnered
with a major paint company in hopes of bringing it to the wider public.
For the "PBS NewsHour," I'm John Yang in West Lafayette, Indiana.