Prompt rewetting of drained peatlands reduces climate warming despite methane emissions

Drained peatlands currently emit about 2 Gt CO2 per year via microbial oxidation and fires, accounting for roughly 5% of anthropogenic greenhouse gas emissions from only 0.3% of global land area. Emissions from drained peatlands between 2020 and 2100 could consume 12–41% of the remaining greenhouse gas budget compatible with limiting warming to +1.5 to +2 °C. Rewetting is a cost-effective mitigation option because it halts CO2 emissions, but it restores methane (CH4) emissions, raising concerns due to CH4’s strong radiative efficiency and uncertainties in emission magnitudes. The climate trade-off is time-dependent because long-lived gases like CO2 and N2O accumulate and their forcing depends on cumulative emissions, whereas short-lived CH4’s forcing depends on sustained emission rates and atmospheric lifetime. Common metrics such as GWP obscure temporal dynamics. The study asks how the timing and extent of peatland rewetting influence radiative forcing trajectories and peak warming, and whether CH4 emissions from rewetted peatlands undermine the mitigation benefits of stopping CO2 emissions.

Prior work highlights the significant role of peatlands in climate mitigation and the substantial contribution of drained peatlands to global emissions. Several studies report high and sometimes elevated CH4 emissions in rewetted systems compared to pristine peatlands and discuss transient CH4 peaks after rewetting. Methane’s strong but short-lived climate forcing and uncertainties in its recent global growth have been emphasized. Traditional comparison metrics like GWP and sustained-flux variants may misrepresent the temporal dynamics of short-lived climate forcers versus long-lived gases, motivating time-explicit assessments using radiative forcing trajectories. Proposals to offset peatland emissions with bioenergy crops or wood biomass exist, but similar substitution benefits can be achieved on rewetted peatlands via paludiculture, avoiding continued CO2 emissions from drained soils.

Study design: The authors constructed five global peatland management scenarios representing extreme options and differing rewetting timings and extents: Drain_More (continued drainage at historical net rate), No_Change (2018 drained area fixed), Rewet_All_Now (rewet all drained peatlands 2020–2040), Rewet_Half_Now (rewet half 2020–2040), and Rewet_All_Later (rewet all 2050–2070). Pristine peatlands were assumed climate-neutral for direct anthropogenic effects. Data sources: Drained peatland areas by IPCC climate zones (boreal, temperate, tropical) and land-use categories were taken from the Global Peatland Database (GPD), including UNFCCC inventory data and NDCs. Arctic drained peatlands (~100 kha) were neglected due to small area and uncertain emission factors. The baseline drained area in 2018 is 505,680 km², with an assumed additional net drainage of ~5,000 km² per year (average 1990–2017). Newly drained and rewetted areas were distributed across zones and land uses proportional to current distributions. Emissions and factors: IPCC 2013 Wetlands Supplement emission factors (EFs) for CO2, CH4, and N2O were applied as sustained fluxes, aggregated to match GPD land-use classes (e.g., grassland and cropland averaged to Agriculture). Emissions from drainage ditches and DOC export were included using IPCC default ditch cover fractions. For CH4 from tropical peat extraction, temperate/boreal extraction EFs were used due to lack of specific values. Sensitivity analysis varied all EFs randomly within 10–20% uncertainty. A potential early CH4 emission peak after rewetting was explored separately (Supplementary Fig. 1). Radiative forcing model: A simplified atmospheric perturbation model using impulse-response functions estimated radiative forcing from CO2, CH4, and N2O fluxes. CH4 and N2O perturbations were modeled as exponential decays; CO2 equilibrated across five pools with different lifetimes (fractions and lifetimes per prior literature). The model assumed a perfectly mixed atmosphere and included CH4’s indirect effects on atmospheric chemistry. Although most peatland CH4 is biogenic, the CO2 from CH4 oxidation was conservatively included, contributing 5–7% of CH4 radiative forcing and ~1–3% of total forcing. Radiative forcing trajectories were compared to IPCC AR5 pathways (starting 2005). Instantaneous global mean temperature effect was approximated as −1 K per 1.23 W m−2 of forcing. Sensitivity analyses: Scenario forcing ranges accounted for uncertainty in net future drainage rates (1,000–8,000 km² yr−1) and EF uncertainties (10–20%), shown via error ranges. The authors note that focusing future drainage in tropics would likely make Drain_More a conservative (underestimated) warming case.

• Rewetting all drained peatlands quickly stabilizes total radiative forcing and then leads to a slow decline, due to halted CO2/N2O emissions and CH4’s short atmospheric lifetime. In contrast, continued drainage or no change increases forcing as CO2 accumulates.
• Methane emissions from rewetted peatlands do not undermine the climate mitigation benefits of rewetting. The long-lived CO2 emissions from drained peatlands dominate long-term warming.
• Timing is critical: prompt rewetting (2020–2040) yields larger climate benefits and better aligns with attenuating peak warming expected after ~2060, whereas delaying until 2050–2070 increases cumulative CO2 and N2O forcing and long-term warming.
• Rewetting only half of drained peatlands (2020–2040) is insufficient to stabilize radiative forcing; ongoing CO2 emissions from the remaining drained areas continue to accumulate and warm the climate.
• Even scenarios that include CH4 emissions from drainage ditches indicate that CH4 forcing in partial rewetting can be less than half that of full rewetting, yet differences among scenarios are primarily driven by CO2 forcing.
• Annual emissions context: Drained peatlands emit ~2 Gt CO2 yr−1 (~5% of anthropogenic GHG emissions) from 0.3% of land area. The potential CH4 oxidation CO2 forcing is relatively minor (5–7% of CH4 RF; ~1–3% of total RF).
• Sensitivity analyses confirm robustness of conclusions under plausible ranges of drainage rates (1,000–8,000 km² yr−1) and EF uncertainties (10–20%).

The analysis directly addresses whether CH4 emissions from rewetted peatlands negate the climate benefits of stopping CO2 emissions from drained peatlands. Because CO2 and N2O are long-lived and cumulative, continued drainage perpetuates increasing radiative forcing and long-term warming. CH4, while potent, is short-lived and its forcing plateau is reached quickly under sustained emissions, so total forcing stabilizes soon after rewetting. Therefore, rewetting reduces peak and long-term warming compared to maintaining or expanding drainage. The study underscores that the proper baseline for evaluation is the drained state with large CO2 emissions; higher CH4 emissions in rewetted versus pristine sites do not argue against rewetting when compared to the drained alternative. Temporal dynamics are essential—acting early maximizes benefits during the period of peak global temperatures projected after ~2060 and reduces risks of crossing climate system tipping points. To align with climate neutrality by 2050 and Paris Agreement goals, rewetting must address (almost) all drained peatlands; selective rewetting is inadequate. Biomass substitution strategies do not necessitate ongoing drainage because comparable substitution benefits can be achieved via paludiculture on rewetted peatlands.

Rewetting drained peatlands reduces climate warming despite associated methane emissions. Using a radiative forcing framework with global scenarios, the study shows that early, comprehensive rewetting rapidly stabilizes and then lowers total forcing, whereas delaying rewetting increases cumulative CO2 and N2O forcing and long-term warming. Partial rewetting is insufficient to halt forcing growth. Policy implication: prompt rewetting of (almost) all drained peatlands is a key measure to mitigate climate change and attenuate peak warming, with CH4 costs being temporary and outweighed by avoided CO2 emissions from drained soils.

• Assumption that pristine peatlands are climate-neutral for direct anthropogenic effects.
• Emission factors derived from IPCC 2013 Wetlands Supplement applied as sustained fluxes; aggregated across categories; true site variability may differ.
• Lack of specific CH4 EF for tropical peat extraction; used temperate/boreal values.
• Simplified atmospheric model assumes a perfectly mixed atmosphere, no climate-carbon feedbacks; impulse-response functions approximate gas lifetimes and pool exchanges.
• Inclusion of CO2 from CH4 oxidation (conservative choice) though most peatland CH4 is biogenic.
• Uncertainties addressed via 10–20% EF variation and drainage rate range (1,000–8,000 km² yr−1), but real-world trajectories could differ, especially if future drainage concentrates in the tropics (Drain_More likely underestimates warming).
• Potential transient CH4 peaks after rewetting not treated in main scenarios; assessed separately in supplementary analysis.
• Did not include potential biomass substitution benefits on drained peatlands; noted that similar benefits are achievable on rewetted peatlands through paludiculture.