The Arctic permafrost is melting National Geographic Image Collection / Alamy Stock Photo

The Arctic has begun releasing more carbon than it is absorbing. The change is a result of climate change thawing frozen ground, and the problem is expected to get much worse as the world warms further.

Previously it appeared some sites in the Arctic had already flipped from being carbon sinks into sources of emissions, but research now shows the phenomenon has happened across the region as a whole.

Vegetation growth in the far north absorbs carbon dioxide across summer, and we had thought that negligible amounts …