The idea is “risky, unproven, even unlikely to work,” according to Y Combinator. But if it did work, it could slow climate change.

Imagine flooding a desert half the size of the Sahara. Using 238 trillion gallons of desalinated ocean water to do the job. Creating millions of 1-acre-square micro-reservoirs to grow enough algae to gobble up all of Earth’s climate-changing carbon dioxide. For an encore: How about spreading the water and fertilizer (the dead algae) to grow a vast new forest of oxygen-producing trees?

A Silicon Valley venture capital firm, Y Combinator, unveiled the radical desert flooding plan as one of four “moonshot” scenarios that it hopes innovators will explore as potential remedies to catastrophic global warming.

But would it work? And should it even be tried?

With unlimited capital and political will — both far from given — experts said the scheme would stand a chance of reducing dangerous greenhouse gas levels. But while they generally believe the climate crisis has become severe enough to push even extreme options onto the table, the experts cautioned against interventions that might create as many problems as they solve.

“We do not want to have this be purely profit driven,” said Greg Rau, a University of California, Santa Cruz climate scientist and part of the team that helped Y Combinator craft the request for proposals. “We are trying to benefit the planet, not just make money. So we need this kind of research and development first, but then oversight and governance over how any of this is deployed.”

The Y Combinator proposal grows out of what is now the consensus of climate scientists — that humanity needs to move beyond slowing the production of carbon dioxide and begin removing excess levels of the gas already straining Earth’s atmosphere.

The startup accelerator that helped finance Airbnb, Dropbox and Reddit asked innovators last month to come forward with specific proposals on desert flooding and three other extreme plans for reducing greenhouse gas concentrations. The existential threat posed by climate change requires research into solutions that the investment firm itself conceded could be “risky, unproven, even unlikely to work.”

Y Combinator said it had a rush of interest in its challenge. It declined to say how many took up the desert flooding option. But Sam Altman, Y Combinator’s president, predicted that in 2019 his firm will fund three companies to pursue the “Plan B” climate solutions.

A host of scientists who have studied Earth’s ecosystems, climate change and bio-engineering said further exploration might be warranted. But they were quick to cite many reasons that desert flooding is not likely to succeed.

Massive size

Y Combinator called filling 1.7 million acres of arid land with 2-meter-deep pools of water “the largest infrastructure project ever undertaken.” Just to pump ocean water inland and desalinate it would require an electrical grid far greater than the one Earth now devotes to all other uses.

“It’s a desert for a reason,” said Lynn Fenstermaker, a research professor at Nevada’s Desert Research Institute. “Flooding the desert and then keeping the water there, in an already water-poor area with all the evaporation, is hard to imagine.”

Y Combinator doesn’t deny the magnitude of the challenge. “Economies of scale as well as breakthroughs in material science and construction technology will all be necessary for success,” its proposal says.

Unprecedented cost

Y Combinator pegs the price tag at $50 trillion. That’s roughly half the entire globe’s economic productivity for a year. Altman said in an interview that the cost for any solution will need to drop into the billions to become more realistic. “You can do a lot of things that require spending more money than you will ever be able to get,” Altman said, “and it just doesn’t come.” Brought to a more realistic price, he believes that governments will pay.

Destruction of unique ecosystems

Many species would be wiped out by massive man-made flooding of deserts. “People think there is nothing valuable in the deserts, but that is far from the truth,” said Henry Sun, a microbiologist and research professor at the Desert Research Center. “These diverse species deserve, and need, the desert to survive.” Most of the world’s countries would set a high bar, Sun said, before destroying habitat.

Potential for making things worse

Interfering with nature can have unexpected consequences. Katherine Mackey, a University of California, Irvine climate scientist, noted how Australia has long tried, and failed, to combat overpopulation of native species by introducing non-native creatures. Famous case in point: toads were introduced in 1935 to tame sugar cane-eating beetles. But the toads couldn’t climb sugar cane. So the beetles thrived, alongside their new neighbors — an out-of-control toad population.

“Saying that we intervened and created a problem with global warming, so let’s further intervene, that’s not the thing to do,” Mackey said. “That’s not how you fix the problem, by replacing it with another problem.”

Distracting from more workable solutions

Climate scientists believe that most, if not all, the needed solutions for limiting new greenhouse gas emissions and reducing current CO2 concentrations already exist. Environmentalist Paul Hawken has catalogued solutions in his Project Drawdown. Taken in total, Hawken has said, they would reduce emissions and sequester enough carbon to more than meet the goals laid out by world leaders in the 2015 Paris climate accord.

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