For years, scientists have pointed to warming permafrost in the Arctic tundra as a source for increased carbon in the atmosphere; as this soil warms, it releases greenhouse gases that have long been trapped in frozen ground.
source https://www.lifetechnology.com/blogs/life-technology-news-blog/scientists-find-carbon-from-thawing-permafrost-is-released-into-the-atmosphere-at-higher-rates-than-previously-thought