Sergey Zimov, right,
and his son, Nikita, run
an Arctic research sta-
tion in Cherskiy, Russia,
along the Kolyma River.
The elder Zimov first
figured out that perma-
frost stores far more
carbon than scientists
once thought. Some
of it is now escaping as
temperatures rise.SERGEY ZIMOV, AN ECOLOGIST BY
training, tossed a woolly mammoth
bone on the pile. He was squatting in
mud along the cool, wide Kolyma River,
below a towering cliff of crumbling
earth. It was summer in eastern Siberia,
far above the Arctic Circle, in that part
of Russia that’s closer to Alaska than to
Moscow. There wasn’t a speck of frost
or snow in sight. Yet at this cliff, called
Duvanny Yar, the Kolyma had chewed
through and exposed what lies beneath:
a layer of frozen ground, or permafrost,
that is hundreds of feet deep—and warm-
ing fast. ¶ Twigs, other plant matter, and
Ice Age animal parts—bison jaws, horse
femurs, mammoth bones—spilled onto
a beach that sucked at Zimov’s boots. “I
love Duvanny Yar,” he said as he yanked
fossils from the muck. “It is like a book.
Each page is a story about the history of
nature.” ¶ Across nine million square
miles at the top of the planet, climate
change is writing a new chapter. Arctic
permafrost isn’t thawing gradually, as
78 NATIONAL GEOGRAPHIC