rozen ground, or permafrost, which underlies 15 per cent of the northern hemisphere and contains twice as much carbon as the atmosphere, has shrunk in area by an estimated 7 per cent in 50 years as it thaws. Recent research suggests the thaw will slow but not stop if we successfully limit global warming to 1.5°C above pre-industrial levels. Scientists, however, haven't been sure whether the permafrost region has become a net emitter of greenhouse gases. Even as the thaw releases more carbon compounds from the once-frozen biological matter in the ground, increased summertime plant growth is absorbing more CO2 from the atmosphere.