The ability of forests to soak up man-made carbon dioxide is weakening, according to an analysis of two decades of data from more than 30 sites in the frozen north.

The finding published today is crucial, because it means that more of the CO2 we release will end up affecting the climate in the atmosphere rather than being safely locked away in trees or soil.

“We are currently getting a 50% discount on the climatic impact of our fossil fuel emissions,” the climate scientist John Miller of the University of Colorado wrote in a commentary on the research in the journal Nature – meaning that half of what we put out is sucked up by the oceans and ecosystems on land.

“Unfortunately, we have no guarantee that the 50% discount will continue, and if it disappears we will feel the full climatic brunt of our unrelenting emission of CO2 from fossil fuels.”

That’s pretty strong language for a scientist…