Ground that's stayed frozen for thousands of years is now starting to thaw

Permafrost, soil that has remained below freezing for at least two consecutive years, underlies roughly a quarter of the land in the Northern Hemisphere and holds plant matter that never fully decomposed. As warming climates thaw it, microbes break down that ancient material and release stored carbon as greenhouse gases, in a feedback loop scientists actively monitor.

— Arctic and climate science literature, Permafrost — carbon-feedback research is an active field