Scientists know why leaves turn yellow in the fall: Chlorophyll breaks down, revealing the yellow pigment that was there all along. But red? Red is a different story altogether. Leaves have to make a new pigment to turn red. Why would a dying leaf do that? Scientists don’t really know. NPR science correspondent Nell Greenfieldboyce reports on the leading hypotheses out there. of Nell's reporting on this topic. Interested in more seasonal science? Email us your ideas at [email protected] to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy

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