Elon Musk has pledged $139 million (US$100 million) to tackle the climate-change crisis.
The Tesla and SpaceX founder offered the hefty reward to whoever is able to develop the best tool to capture planet-warming carbon emissions.
"Am donating $100m towards a prize for best carbon capture technology," Musk tweeted. "Details next week."
Musk recently became the world's richest person, his personal wealth surged to US$185 billion to overtake Amazon boss Jeff Bezos.
Carbon capture involves using machinery to trap carbon dioxide emitted from places like factories before it escapes into the atmosphere.
Capturing planet-warming emissions is becoming a critical part of many plans to keep climate change in check, but very little progress has been made on the technology to date, with efforts focused on cutting emissions rather than taking carbon out of the air.
US President Joe Biden has pledged to accelerate the development of carbon capture technology as part of his sweeping plan to tackle climate change.
Musk's announcement came the same day the Biden administration appointed Jennifer Wilcox, a carbon capture expert and professor of engineering and energy policy at the University of Pennsylvania, Musk's alma mater, as principal deputy assistant secretary for fossil energy at the US Department of Energy.
Meanwhile, as a solution to Miami's notoriously congested traffic, Musk is proposing to dig tunnels with The Boring Company, one of his many business ventures.
Experts say the idea would be costly and is fraught with engineering obstacles, but it's not outright crazy.
Musk, who also founded SpaceX and Neuralink, tweeted that he spoke with Governor Ron DeSantis about the idea earlier this month.
"If Governor & Mayor want this done, we will do it," Musk tweeted. Miami Mayor Francis Suarez, a Republican, described the idea as a "no brainer" and replied, "we would love to be the prototype city."
Miami-Dade Democratic Mayor Daniella Levine Cava and Florida's Republican chief financial officer, Jimmy Patronis, also expressed enthusiasm.
Critics wondered: How plausible is it to build large tunnels under a city that is only a few feet above sea level, especially with Miami widely regarded as one of the world's most vulnerable cities to rising sea levels?
"It doesn't seem very smart and it is certainly going to be expensive," said Kurtis Gurley, a professor of structural engineering at the University of Florida.
Gurley said one challenge of the project would be keeping water out of the tunnels while shoring up its walls.
The subterranean construction also runs the risk of contaminating Florida's aquiferm, Gurley said.