Source or sink? A review of permafrost's role in the carbon cycle

Permafrost, or ground that is frozen for two or more years, stretches over about 14 million square kilometers in the Northern Hemisphere, 15% of the hemisphere's land area. Cold temperatures limit the decomposition of organic material, making permafrost soils a significant carbon sink. But warming temperatures from climate change are thawing permafrost and allowing microbes to decompose stored carbon. The result is a release of greenhouse gases, creating a feedback loop that further drives warming climate conditions.