Large parts of the territory affected by the fires were once peat bogs: https://www.researchgate.net/profile/Dan_Hammarlund/publication/264039044/figure/fig1/A

Large parts of the territory affected by the fires were once peat bogs: https://www.researchgate.net/profile/Dan_Hammarlund/publication/264039044/figure/fig1/AS:296035403485193@1447591748394/Figure-1-Location-of-study-sites-Map-showing-the-distribution-of-northern-peatlands.png https://www.researchgate.net/profile/Dan_Hammarlund/publicat... The carbon in those was sequestered; under normal circumstances, it would remain buried for millennia.