Peatlands can either absorb or emit CO2
Peatlands are the world’s largest natural terrestrial carbon store. Peatland stores more carbon each year than all other vegetation types in the world combined . Peatlands contain about two thirds as much carbon as is stored in the earth’s atmosphere.
At present, peatlands help to cool the climate.
But large areas of peatlands have already been damaged by human activity and global warming, and this makes them a major source of greenhouse gas emissions. Annually, damaged peatlands release almost 6% of global anthropogenic CO2 emissions.
Around half of all peatland is near the Arctic and is frozen in permafrost for most or all of the year. Global warming is resulting in more and more of this peatland being thawed out each year. Thawed peat decomposes, releasing CO2 and methane.
On 10 August a new map was published  showing the northern peatlands and their carbon and nitrogen stocks. The authors used these maps to model the impact of permafrost thaw on peatlands and find that warming will likely shift the greenhouse gas balance of northern peatlands.
While peatlands cool the climate today, anthropogenic warming can shift them into a net source of warming.
When will this happen?
“Unfortunately, we cannot put exact times to these numbers so far, the models are not that advanced yet,” said lead author Gustaf Hugelius from Stockholm University, Sweden, “but my best estimate is that this shift will occur in the second half of this century.” 
The report authors say that their new estimate of the carbon emitted through thawing, and from losses of peat into rivers and streams, is 30-50% greater than in previous projections of carbon losses from permafrost thawing.
 International Union for Conservation of Nature (IUCN), https://www.iucn.org/resources/issues-briefs/peatlands-and-climate-change