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Photographer: Martin Leissl/Bloomberg Photographer: Martin Leissl/Bloomberg

A Stanford University professor whose research helped underpin the U.S. Democrats’ Green New Deal says phasing out fossil fuels and running the entire world on clean energy would pay for itself in under seven years.

It would cost $73 trillion to revamp power grids, transportation, manufacturing and other systems to run on wind, solar and hydro power, including enough storage capacity to keep the lights on overnight, Mark Jacobson said in a study published Friday in the journal One Earth. But that would be offset by annual savings of almost $11 trillion, the report found.

“There’s really no downside to making this transition,” said Jacobson, who wrote the study with several other researchers. “Most people are afraid it will be too expensive. Hopefully this will allay some of those fears.”

Some of Jacobson’s past findings have been questioned, notably a 2017 journal article that criticized his methodology on measuring the cost of phasing out fossil fuels.

The biggest challenge of ditching fossil fuels may not be economic. Even some clean-power advocates acknowledge technology isn’t available yet to run power grids entirely on renewables without jeopardizing reliability.

The report published Friday looked at 143 countries that generate more than 99% of the world’s greenhouse emissions. The savings would come from not extracting fossil fuels, using higher-efficiency systems and other benefits of shifting entirely to electricity. It follows a paper Jacobson published in 2015 laying out a state-by-state plan for the U.S. to convert to 100% renewables.