Peatland Restoration and the Carbon Question

AA drained bog is one of the few landscapes that can be watched losing carbon: the surface sinks, the ditches run brown, and a metre of peat that took a thousand years to form can disappear within a single working lifetime. Putting the water back is therefore among the simplest climate measures available, and it has been treated as an unambiguous gain by the markets that have grown up around it. Since 2019 several European schemes have sold credits on that basis. The difficulty is that the ledger does not close as neatly as the picture suggests, because water does not merely halt the loss of carbon dioxide; it also begins something else. Saturated ground excludes oxygen, and the microbes that thrive in its absence release methane, a gas whose warming effect per tonne is many times that of carbon dioxide. Every restored site therefore spends a period during which it is, in strict accounting terms, worse for the climate than the drained field it replaced. How long that period lasts is the whole of the argument.

BMarion Delacroix, a biogeochemist at the Kilbride Institute of Wetland Science, maintains that the period has been consistently underestimated, and she blames the instruments rather than the science. Almost all early figures came from static chambers, closed boxes set for an hour at a time on the drier hummocks where a researcher can kneel without sinking. Such places are the least active part of a rewetted bog. Between 2015 and 2022 her group instead ran continuous towers over twelve restored sites in northern Europe, an approach that samples everything carried on the wind past the mast, including the wettest ground. The towers found that most of the gas leaving a crudely rewetted site escapes from ditch pools rather than from the moss between them, and that the chambers had therefore missed the dominant source. Her revised estimate places the crossing point, at which a restored site has repaid the warming it caused, at a median of 32 years rather than the eight commonly assumed. The correction, she insists, does not argue against restoration; it argues against selling it too soon.

CTomas Hedlund, who advises restoration schemes for the Norrvik Peatland Trust, does not dispute that ditch pools are the dominant source; his objection is that they need not exist at all. Blocking a ditch with a bank of peat and walking away produces standing water, whereas a properly engineered scheme re-profiles the surface so that the water table is held some five to ten centimetres below the moss and never allowed to reach the surface. On three such sites monitored between 2021 and 2023, emissions were roughly a quarter of those Delacroix reports, and the crossing point falls below fifteen years. The difference is a matter of engineering, not of chemistry. Delacroix's towers, he contends, are measuring the failures of a first generation of projects and are being read as though they described the technique itself. The weakness of his own case is one he concedes readily: three sites, two seasons and a single climate cannot support a general figure, and the sites available to him were also those whose peat had been degraded least before work began. Whether the low emissions follow from the engineering or from the state of the ground he cannot yet say.

DBoth figures can be correct at once, because the question contains a choice that is rarely made explicit: the length of the period over which the sums are done. Methane is powerful and short-lived, breaking down in the atmosphere within about twelve years, whereas the carbon dioxide released by drained peat persists for centuries. Measured over only twenty years, a freshly rewetted bog is a liability, since the methane is at its peak while the avoided carbon dioxide has barely accumulated. Measured across a hundred, the same site is a clear benefit, and the early methane becomes a transient cost of a permanent gain. Neither accounting period is wrong. What is wrong, and here the two researchers say almost the same thing in almost the same words, is to choose the horizon after seeing which answer it produces, a practice that spreads wherever credits must be sold before the ground has settled. Delay is not a neutral option either, since peat left drained continues to oxidise at rates of five to twenty tonnes of carbon dioxide per hectare each year.

EThe consequence for policy is less about ecology than about what a purchaser is actually buying. Credits granted on the evidence of the first decade are, on Delacroix's figures, sold before the site has begun to repay the warming it caused, and they cannot be recalled once the accounts have been audited. Both researchers therefore favour paying against a measured condition rather than against an action, so that money follows a water table held at a stated depth through a stated number of summers, not a ditch dam and a photograph. Verification of that kind is expensive, absorbing between eight and fifteen per cent of scheme revenue in the first European trials, which is why it is resisted. It is also the only version of the scheme that survives contact with Hedlund's evidence, since his central claim is precisely that outcomes depend on how the work is done. The writer's own position is that restoration is worth carrying out on every hectare where it is feasible. It is the certificate, rather than the bog, that should be made to wait.