This happens because of the physics of rain storms, Leung said.
Not only can the atmosphere hold 4% more moisture per degree Fahrenheit (7% per degree Celsius), but it’s what happens in the storm that changes and makes the precipitation come down even more, Leung said. You’ve got air rising inside the storm with more water vapor condensing to produce rain and snow; it then releases heat “that kind of causes the storm to become more vigorous and stronger,” she said.
When water vapor condenses it comes down as rain and snow along the edges of the storm, but heating sort of squeezes that falling precipitation in toward the middle, Leung said.
“The concepts and impacts of how precipitation features are likely to change are well quantified and well explained,” said David Gochis, an expert in how water affects the weather at the National Center for Atmospheric Research in Boulder, Colorado, who wasn’t part of the study.
When she used computer simulations, Leung chose the most severe worst-case scenario for how the world’s carbon emissions will grow. It’s a scenario that used to be called business as usual, but the world is no longer on that track. After years of climate negotiations and the growth of renewable fuels the globe is heading to less warming than the worst case, according to climate scientist Zeke Hausfather of the tech company Stripe and Berkeley Earth.
“We are providing more of a worst-case scenario, but understanding that if we do take action to reduce emissions in the future, we could end up better,” Leung said. “If we control the emissions and lower the global warming in the future, we can limit the impacts of climate change on the society, particularly flooding and extreme precipitation that we are talking about in this study.”