World’s ‘vital’ peatlands could shift from being key carbon sink to major source of greenhouse gas

Peat is an enchanting substance. Earthy, mossy, and almost oily, it is a rich accumulation of living, dying and dead plant matter, and is the most efficient carbon sink on the planet.

Known as the “forgotten fossil fuel”, peat takes thousands of years to form in substantial quantities, and though peat bogs cover just 3 per cent of the surface of the earth, they store more carbon than all the world’s forests combined, holding one-third of the Earth’s soil carbon.

For this reason, researchers have warned the preservation of peat is “vital” in the battle against the worsening climate crisis and global environmental breakdown.

The world’s peatlands are under threat from a variety of different sources, including agricultural expansion - which has seen peat bogs drained and cultivated; the cutting and harvesting of peat for burning and use in horticulture, and rising temperatures, which can critically impact peatlands’ ability to store carbon.

A new study, led by the University of Exeter and Texas A&M University, has examined peatland losses over human history and warns these will be “amplified” in the future.

The warming world is a key reason why peat’s continued existence is more precarious.

When peat dries out, due to human drainage, or due to unusually dry weather, the organic carbon – which has remained in place for thousands of years and is normally underwater – is suddenly exposed to the air. It decomposes and turns into the greenhouse gas carbon dioxide.

Wildfires in peatlands release vast amounts of carbon dioxide very rapidly, and due to their depth - peat bogs can extend for several metres below the surface - light rain may not extinguish the fires, which can smoulder for months, even surviving winter - these are known as zombie fires.

For this reason the world’s peatlands are expected to shift from an overall “sink”, absorbing carbon, to a source of carbon this century - a change which would exacerbate the climate emergency.

This is primarily due to human impacts across the tropics, where many peatlands have been drained and where higher temperatures can undo the carbon storing capabilities of the peat.

The study warns more than 100 billion tons of carbon could be released from peat over the next 80 years, although uncertainties remain large.

“Peatlands contain more carbon than all the world's forests and, like many forests, their future is uncertain,” said professor Angela Gallego-Sala, of Exeter's Global Systems Institute.

“Peatlands are vulnerable to climate change impacts such as increased risk of wildfires and droughts, the thawing of permafrost and rising sea levels.”

Professor Gallego-Sala told The Independent: “One of the main agents of change in the recent past has been temperature – as the climate warms, peatlands at high latitude experience longer growing season lengths [therefore] plants have a longer time to photosynthesise and this leads to more input into the peatland systems.

“At the same time, decomposition processes in the soil also speed up. But of these two processes photosynthesis wins and these systems accumulate more carbon - this is good.”

But she warned: “This is the case only at high latitudes and in the future this is likely to lead to more carbon being stored in peatlands, if they are not drained.

“In the tropics, where the growing season length is already as long as it can be (all year round) warmer temperatures only increase decomposition – so here carbon losses are expected in the future due to increases of temperatures and also changes in moisture conditions.”

She added: “Drainage of peatlands to convert to agriculture has already led to huge losses of carbon and will continue to do so unless we realise their importance and put incentives in place to keep that carbon locked away in the peatland soil.

“These systems are not normally fire prone, as they are very wet, but once you drain them they are easy to ignite and difficult to stop burning because they smoulder, even sometimes below the surface.”

Though peatlands are found in almost every country on Earth, Professor Gallego-Sala said they have been “overlooked” in some climate models because they are seen as “inert” - neither absorbing nor emitting carbon at a rapid rate when left alone.

This exclusion from climate models makes it hard to estimate future changes, so the study combined existing research with survey estimates from 44 leading peatland experts.

Based on this, it estimates total carbon loss from 2020-2100 at 104 billion tons.

The authors said this estimate is highly uncertain (losses up to 360 billion tons to gains of 103 billion tons) - but it demonstrates the need both for inclusion in models and better peatland preservation.

“Even though we would like more information, we clearly need to make decisions now about how we manage these ecosystems,” professor Gallego-Sala said.

“We simply can't afford for peatlands to go up in smoke.”

New discoveries of tropical peatlands in the Amazon and Congo are mainly intact, and the researchers say it is important to make sure we have solid policies in place.

“We have a responsibility to find a way forward that works for people and the planet,” professor Gallego-Sala said.

“Where people have a strong economic incentive - or even necessity - to destroy peatlands, we need plans and policies that offer more sustainable alternatives.

“The future of peatlands is very much in our hands.”

The study is published in the journal Nature Climate Change.