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NOVA: Can We Cool The Planet?

Rising Sun and Earth's horizon
Courtesy: NASA/JSC
Rising Sun and Earth's horizon

Wednesday, April 27, 2022 at 9 p.m. on KPBS TV / On demand now with PBS Video App

“Can We Cool The Planet?” takes a fresh approach to covering the climate change crisis by investigating new technologies that may help delay the most devastating impacts. As wildfires rage in the American West and extreme weather sparks civil unrest around the globe, it is clear that emission reductions alone may not prevent the dire effects of climate change.

In response, scientists and engineers are opening another front in the battle to combat climate change by developing technologies that can help us cool the planet — from enhancing our atmosphere’s natural ability to reflect sunlight, to sucking carbon dioxide right out of the air, to enlisting plants.


NOVA joins scientists and skeptics alike to explore the controversial landscape of geoengineering — the effort to build controls for Earth’s thermostat. As the calls for action become more urgent, do we understand the potential risks of these unproven technologies?

NOVA: Can We Cool the Planet? Promo

Experts agree that the first step for cooling the planet is preventing CO2 from entering the atmosphere. At the same time, we can find ways to remove it.

Throughout the special, viewers discover the different ways that scientists and engineers are trying to tackle carbon, including:

But, even if these new technologies can scale up to their full potential individually they could only offset a fraction of the world’s emissions.

Can Geoengineering “Undo” Climate Change?

As scientist David Keith explains, “We will get to the day where there’ll be global celebrations, where we get to net zero day where we brought human CO2 emissions to zero ... But on that day, we have not solved the climate problem. All we've done is stop making it worse ...”


If we can’t reduce our carbon emissions fast enough, are there technologies that can offer a backstop to extreme climate risks? One method scientists are exploring is changing the reflectivity of the planet — making Earth cooler, for example, by brightening clouds. Clouds play a critical role in controlling Earth’s temperature by
reflecting solar radiation back into space.

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Sarah Doherty and Armand Neukermans of the Marine Cloud Brightening Project are researching whether we can enhance this phenomena to bounce more light, and heat, back into space. They are designing a nozzle system to produce saltwater particles of an optimal size and speed to propel them into marine clouds.

Research into the side effects of this method on the surrounding ecosystems is still developing, but outdoor experiments have already begun near the Great Barrier Reef in efforts to cool the waters surrounding the coral.

Marine Cloud Brightening is designed to produce localized cooling, but David Keith and Frank Keutsch at Harvard are exploring whether adding reflective particles to the stratosphere could cool the entire planet. To better understand the effects of this form of solar geoengineering, Keutsch and Keith are designing a first of its kind experiment called SCoPEx.

But with so much uncertainty, some scientists think we are better off investing in a different kind of machine, one developed over millions of years in nature’s own laboratory, with a proven record of safely drawing down CO2 levels: trees.

Cutting our Greenhouse Gas Emissions to Zero

“Can We Cool The Planet?” introduces scientists exploring natural methods of carbon-capture:

  • NASA research scientist Lola Fatoyinbo-Agueh, who uses terrestrial and space-based lasers to measure the amount of carbon stored within forests
  • The team at the Crowther Lab at ETH Zurich, which employs artificial intelligence and machine learning to identify where forests can be expanded globally to draw down carbon dioxide and to predict exactly how many trees we could plant and how much CO2 they could absorb
  • Whendee Silver, who turns agricultural waste into compost, reducing methane emissions and boosting carbon uptake in soil
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Throughout the film, experts Scott Denning of Colorado State University, Jane Long from The California Council of Science & Technology, Sheila Jasanoff of Harvard’s Kennedy School and Steve Pacala from Princeton University analyze these emerging technologies and offer perspective on each solution’s capacity to address the world’s rising temperatures and control heat in the stratosphere on a global scale.

Three Solutions That Can Slow or Stop Climate Change

While no singular technology offers a silver bullet, rapid changes to Earth’s climate mean we have already reached a dangerous tipping point, and as a result, public demand for alternative solutions is rising. As technologies once considered futuristic or taboo enter the mainstream, it’s critical that we evaluate them soberly, with optimism for the potential they offer, as well as appropriate caution for the risks they carry.

“Can We Cool The Planet?” pushes scientists and viewers to ask the hard questions as time runs out on conventional solutions to climate change, such as: Can geoengineering can really work? How much would it cost? And what are the risks of engineering Earth's climate?

If there is one thing experts can agree on it’s that there is no perfect solution, but we have to start really looking at what can scale up, and be maintained for decades, if not centuries.

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Filmmaker Quotes:

“During production, each scientist we followed echoed more or less this sentiment: ‘There is no silver bullet to solving climate change, only silver buckshot.’ That sums up what we learned in 'Can We Cool The Planet?' While it’s natural to look to these fresh new ideas with hope and optimism, so many of them are still in their infancy. As every scientist in this film agrees, no technology on its own can fix the problem we face,” says filmmaker Ben Kalina.

“That said, as climate change ripples across the planet, the question has shifted from ‘should we research these unknown technologies’ to ‘which technology can scale up most quickly and be the least disruptive?’ adds filmmaker Jen Schneider. “We must be hopeful, but also cautious and data-focused as we think about stepping into this new era of climate risk management — and a geoengineered world.”

Watch On Your Schedule:

This episode is available for streaming simultaneously on all station-branded PBS platforms, including and the PBS Video App, which is available on iOS, Android, Roku, Apple TV, Amazon Fire TV and Chromecast, for a limited time.

Extend your viewing window with KPBS Passport, a benefit for members supporting KPBS at $60 or more yearly, using your computer, smartphone, tablet, Roku, AppleTV, Amazon Fire or Chromecast. Learn how to activate your benefit now.

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A NOVA production by Mangrove Media LLC for GBH Boston in association with ARTE France. Produced by Ben Kalina. Co-Produced by Frauke Levin. Director of Cinematography is Jen Schneider. Edited by Rob Tinsworth. Written and Directed by Ben Kalina and Jen Schneider. Senior Producer for NOVA is Caitlin Saks. Executive Producers for NOVA are Julia Cort and Chris Schmidt. NOVA is a production of GBH Boston.