Damaged peatlands in England are leaking as much carbon into the atmosphere each year as the emissions of 350,000 households, according to an audit of the habitat by Natural England.
The government's conservation agency carried out an assessment of the extent and condition of English peatlands and found that almost three-quarters of deep peat areas in the country are now damaged or degraded.
Peatlands are a vital store of carbon, which they lock into the soil, but it is released if the peat is drained, dried, burned, cultivated or cut for horticultural uses.
Natural England warned the reservoir of some 580 million tonnes of carbon within the peat was slowly leaking back into the atmosphere.
The country's peatlands are estimated to be releasing almost three million tonnes of carbon dioxide a year - equivalent to the annual emissions of more than 350,000 households.
And the natural mechanisms which would allow them to absorb and store up more new carbon have been disrupted by the damage.
According to the England's Peatlands report, around two fifths of deep lowland peat is now under cultivation and more than a fifth (22 per cent) is drained for livestock grazing.
Almost a third (30 per cent) of upland blanket peat is under moorland which is burnt on rotation, while more than a fifth of blanket peat has been dried out by shallow moorland drains.
And around 14 per cent of peatland areas are marked by "haggs" and gullies, as the peat is exposed and eroded.
Natural England is calling for widespread restoration of degraded peatland through "re-wetting" dried-out bogs, and minimising damaging practices on the land.
Looking after peatlands would not only preserve carbon stores but also contribute to efforts to reduce flooding, improve the quality of water supplies and protect rare wildlife, the conservation agency said.
Natural England's chief executive officer Helen Phillips said: "This report is a wake-up call - England's peatlands are a crucial buffer against climate change but have been extensively damaged by centuries of inappropriate management.
"We have to stop the rot and ensure that peatlands are properly looked after as one of our most precious environmental resources."
She added: "Their condition has major implications for our response to climate change, the alleviation of flooding, the quality of our water supplies and the future of many rare and important species.
"Our report has shown the value of peatland restoration in the battle against climate change and we should do all we can to give peatlands a more sustainable future."