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Greater daytime cloud cover may be shrinking the difference between daily high and low temperatures in parts of the world, new research suggests.

Nights are heating up faster than days across much of the globe, narrowing the daily temperature difference. In the U.S., the daily low has warmed twice as fast as the daily high. Researchers have posited this is happening because warmer air holds more moisture, and moisture traps heat, allowing high temperatures to persist into the night. Experts have also suggested the temperature gap is shrinking because nights are simply more sensitive to warming, with the layer of air just above the ground heating up more readily after sunset.

For the new study, scientists modeled future climate change in central Japan and Malaysia, finding that the temperature gap will shrink by around 0.5 degrees C in Japan and 0.25 degrees C in Malaysia by the end of this century, thanks primarily to greater daytime cloud cover seen with warming. Clouds reflect the sun’s light, cooling the area below, leaving days to warm more slowly than nights. The findings were published in the journal Geophysical Research Letters.

While scientists have previously proposed that clouds may be shrinking the temperature gap by reflecting sunlight, this study is the first to use high-resolution computer modeling to investigate the question. “Clouds are one of the big uncertainties in terms of climate projections,” Dev Niyogi, a climate scientist at the University of Texas and coauthor of the study, said in a statement. “When we do this with a very high spatial resolution modeling framework, it allows us to explicitly simulate clouds.”


Why Clouds Are the Key to New Troubling Projections on Warming

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