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As carbon dioxide and other greenhouse gasses build up in the dense lower atmosphere, they absorb heat and keep it trapped there.

Hydrogen is a promising source of energy that produces water vapor instead of carbon dioxide as its byproduct, which proponents say could be used to power hard-to-decarbonize industries such as steel production, manufacturing and transportation.

But carbon dioxide emissions, which warm the planet, have risen to an all time high, the report says, with hot weather pushing up the overall demand for power.

Depending on the type of rocket fuel used, launches produce nitrogen oxides, chlorine, black carbon particles, water vapor, carbon monoxide and carbon dioxide — and no propellant avoids creating of some kind of emissions.

The seven hydrogen hubs were collectively expected to produce 3 million metric tons of hydrogen each year — reducing 25 million metric tons of carbon dioxide emissions, or roughly the amount of 5.5 million gas-powered cars.