NASA forecasts more rain in future

A new NASA study warns that the amount of rain that will fall in Earth's tropical regions will increase as our planet continues to warm.

According to the new study published in the journal Nature Communications, most global climate models may underestimate the decreases in high clouds over the tropics seen in recent NASA observations.

Globally, rainfall isn't related just to the clouds that are available to make rain but also to Earth's "energy budget" -- incoming energy from the sun compared to outgoing heat energy, according to the study, titled "Tightening of Tropical Ascent and High Clouds Key to Precipitation Change in a Warmer Climate."

High-altitude tropical clouds trap heat in the atmosphere, but if there are fewer of these clouds in the future, the tropical atmosphere will cool, and cooling water vapor in the cold upper atmosphere condenses it, turning it into liquid droplets - rain, or ice particles. It releases its heat and warms the atmosphere.

Judging from observed changes in clouds over recent decades, it appears that the atmosphere would create fewer high clouds in response to surface warming. It would also increase tropical rainfall, which would warm the air to balance the cooling from the high cloud shrinking, according to the research, led by Hui Su of U.S. space agency NASA's Jet Propulsion Laboratory in Pasadena, California.

"This study provides a pathway for improving predictions of future precipitation change," Su said in a statement.

Compared climate data from the past few decades with 23 climate model simulations of the same period, the research team found that most of the climate models underestimated the rate of increase in precipitation for each degree of surface warming that has occurred in recent decades.

For data, the team used observations of outgoing thermal radiation from NASA's spaceborne Clouds and the Earth's Radiant Energy System (CERES) and other satellite instruments, as well as ground-level observations.

The models that came closest to matching observations of clouds in the present-day climate showed a greater precipitation increase for the future than the other models, the study said.3

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