Why Do Leaves Change Color in Autumn?

Every autumn, billions of leaves turn yellow, orange and red, and millions of people travel to see them. But why do leaves change color at all? We follow the science: why chlorophyll makes leaves green, the yellow pigments hiding in every leaf all summer, how trees recycle nitrogen before winter, why red is made from scratch (sunscreen or a warning to aphids?), the ice-age idea that may explain why Europe's autumns are mostly yellow, and how drought and a warming climate change the show. Plus: why you should leave some of the leaves. CHAPTERS 0:00 Intro 0:56 Chapter 1 – Why leaves are green 2:03 Chapter 2 – The hidden yellow 3:49 Chapter 3 – Why drop leaves at all 5:28 Chapter 4 – The mystery of red 7:29 Chapter 5 – Why Europe turns yellow 9:11 Chapter 6 – Weather and a warming world 10:55 Chapter 7 – Leaf peeping and leaf piles 12:12 Wrap-Up – Recap KEY FACTS • Chlorophyll absorbs red and blue light and reflects green; in autumn the tree stops replacing it • Yellow and orange carotenoids are in the leaf all summer, masked by green • A fallen leaf may keep only ~40% of its summer nitrogen; the rest is pulled back into the tree • Ripe bananas glow blue under UV light because of chlorophyll breakdown products (Moser et al., 2008) • Red anthocyanins are newly made in autumn; in red-osier dogwood, red leaves recovered from strong light while yellow ones did not (Feild et al., 2001) • Hamilton & Brown (2001): fewer aphids on trees with bright autumn colours • Lev-Yadun & Holopainen (2009): Europe's east–west mountains may explain its yellow autumns • Zani et al., Science 2020: more spring/summer growth → earlier leaf fall; projected 3–6 days earlier by 2100 in Central Europe Some ideas in this video (why leaves turn red, why Europe is yellow) are still debated by scientists. SOURCES Farmers' Almanac 2026 Fall Foliage Outlook; WSET (Virginia), 23 Sep 2026; AFP via Malay Mail (Vermont foliage tourism, Acadia peak timing); USDA Forest Service (leaf color science); Moser et al., Angewandte Chemie 2008 (ScienceDaily); Cary Institute / EarthWise Radio (nitrogen resorption); Feild, Lee & Holbrook, Plant Physiology 2001; Hamilton & Brown, Proc. R. Soc. B 2001 (Carl Zimmer); Lev-Yadun & Holopainen, New Phytologist 2009 (Live Science); Zani et al., Science 2020 (Popular Science); Xerces Society "Leave the Leaves". #Autumn #FallLeaves #Science #Nature #StickFigures #Explained