Permafrost has been frozen and stable, in many cases for thousands of years. This packed ground surface holds organic material that has decomposed, producing methane that has been kept out of the atmosphere because of the cold. Methane which, as a greenhouse gas, is far more dangerous than carbon dioxide. As the climate warms, permafrost areas as deep as 30 feet are getting warmer. Thawed permafrost, even if only slightly above freezing, releases the methane which increases global warming which increases the amount of thawed permafrost. That circular pattern is accelerating and can only be controlled by reducing overall climate change. That, in turn, requires immediate cessation of fossil fuel use.
https://thinkprogress.org/dangerous-permafrost-climate-feedback-loop/amp/