Greenhouse gas (GHG) emissions arising from the fire disturbance of tropical peatlands have been highlighted in several recent studies 1 because of the potential for ongoing emissions and also for opportunities to sequester carbon (C) through restoration of degraded peatlands 2. Tropical peatlands are a globally significant terrestrial store of C estimated at around 105 Pg 2. Large areas of peatlands support forests across the tropics, with 47% of the total tropical peatland area in Indonesia, where it comprises 65% of the tropical peatland C pool, sequestering around 57 Pg of C. More generally tropical peatlands are around 5–6% of the global soil C pool, with Indonesian peatlands accounting for about 3% of global soil C.
Forest biomass burning is a major source of global anthropogenic emissions, with CO2 emissions from wildfires averaging 2.2 Pg C yr− 1 3 – equivalent to 22% of the global fossil fuel emissions 4. Indonesia is a global hotspot for C sequestration in peat swamp forests and peatlands more generally (Page et al. 2017) and emissions from Indonesian peat fires in 1997 were reported to have released 810–2570 Tg C (0.81–2.57 Gt C), equivalent to 13–40% of the mean annual global carbon emissions from fossil fuels accounted 5. These emissions estimates exceed by five times the ca 500 Tg C estimated by the Global Fire Emissions Database (GFEDv4) for the same fires 3. While field based estimates of released emissions from peat fires as reported in 5) should have been more accurate than modelling, those empirical estimates were based on a single value of peat carbon content and of aboveground biomass applied to both degraded peatlands and to intact forests see Table 2 in 5.
Reducing atmospheric CO2 concentration and keeping global warming at bay was the focus on the recent COP 26 Climate Summit in Glasgow 2021, and reducing smoke and emissions specifically from peat fires has gained national and international significance as a mechanism for addressing climate change. For these reasons the Food and Agriculture Organisation (FAO) of the United Nations (UN) has recently declared that improving the assessment of GHG emissions from peatlands is a global strategic priority 6. Improving the assessment of GHG emissions from peatlands will allow for the development of policy that establishes incentives to achieve peatland restoration at an economy scale, particularly through schemes such as REDD+. Several studies over the last two decades have documented the rapid degradation of tropical peatlands, with clearing and drainage are often followed by frequent fires and development of agriculture and plantations over large areas of former peat swamp forest 7, 8. The opportunity for conserving and restoring tropical peatlands is a priority for climate change mitigation as well as biodiversity conservation and water resource protection. In reviewing the published literature for studies that support fire emission estimation parameters for tropical peatlands 9 showed a lack of published studies to support peat fire emission estimates – the aboveground mass of potential fuels (MAG) and their combustion completeness (CfAG), and depth of burn into the peat (h) and peat bulk density (BD), peat combustion factor (CfPEAT) require further attention.
International pressure on Indonesia to reduce emissions from peat fires is enormous yet the magnitude of emissions released to the atmosphere is uncertain. This uncertainty is partly due to different approaches to account for emissions from the diversity of peatland landscapes that have evolved from the initial fire occurrence, that may or may not have followed initial logging. Peat swamp forests (PSF) degraded by logging and fire may subsequently become fragmented secondary forests, plantations on peat, or repeatedly fire-impacted degraded peatlands. These varying outcomes for peatland landscapes from frequent fires are rarely accounted in peat-related emission studies, with studies often relying on the default parameters provided in the Guideline of the Intergovernmental Panel on Climate Change IPCC 10).
Initial methodologies for estimating emissions from biomass burning were published in 1996 11. The parameters required for estimating emissions are the activity data (AD, or area burnt) and emission factors (EF), the mass of the fuel available for combustion, multiplied by the fuel combustion factor (Cf) and a gas specific emission factor (Gi). Cf refers to how much fuel is combusted (or released to the atmosphere) and Gi refers to the amount of i greenhouse gas (i.e., CO, CH4, N2O) emitted per kg of fuel burnt. Emissions are reported in CO2-equivalent and thus global warming potential (GWP) for each of the reported gases is also required. These parameters are continuously updated as research advances and technologies progress (especially for Gi) and as we learn more about ecosystems dynamics.
For biomass burning, the United Nations Framework Convention on Climate Change (UNFCCC) encourage non-Annex I Parties to provide information on anthropogenic emissions by sources of: CO2, CH4, N2O (Decision 17/CP.8, annex, paragraph14), CO, NOx, and non-methane VOCs (Decision 17/CP.8, annex, paragraph16). The challenges developing countries face are that many of the parameters required for the emission estimates are either derived from scientific publications that are only available by subscription, or cost 30–60 dollars per individual publication or, non-existent such as data for GWP for NOx 12. For many gases, such as non-methane volatile organic compounds (NMVOC) or NOx -a short for nitric oxide (NO) and nitrogen dioxide (NO2), specific Gi are not easy to identify for staff responsible for the national level reporting, who may not have a chemistry background. Thus, on the one hand, it is a good practice to report emissions as comprehensively as possible, but on the other hand many countries lack the experience and knowledge (capacity) to do so.
The UNFCCC established the REDD + scheme as a means for developing countries to receive result-based payments for reducing emissions from deforestation and forest degradation. To achieve REDD + compliance each country is required to establish a forest reference level (FRL) or forest reference emissions level (FREL) and a process for monitoring, verification and reporting of annual forest carbon stock changes and emissions. The uptake and overall success of the REDD + scheme require that each country develops expertise in GHG emissions reporting – a significant step given the complexities of the policy, the underlying science, and the many steps to implementation. For these reasons capacity building is an essential component of climate change mitigation and adaptation initiatives that are promoted through UNFCCC mechanisms. Countries where emissions from biomass burning is one of the major sources of global emissions need access to appropriately skilled and experienced staff to complete emissions reporting and related governance steps, so that training, science and technology transfer, capacity building are required to ramp up emissions reduction ambition. Emissions reporting may also rely on the availability of relevant peer-reviewed publications to provide a transparent and defensible scientific basis for selected methodologies.
As an example of the complex nature of emissions reporting, the Government of Indonesia (GoI) did not report peat fire emissions for its first FREL submitted in 2016, due to a high level of uncertainty in the estimates, but instead included them in the Appendix 13. Emissions from peat fires were included in their second FREL submission in 2022 FREL due to improved capacities and the availability of recently published data for estimating CfPEAT 14. This is a significant development for the improvement of global emissions estimates, because Indonesia’s 2016 FREL was based on a simple method, that calculated CO2 emission by multiplying mass of peat burnt by peat carbon content. This approach overestimated CO2 emission as it assumed that all carbon burnt is released as CO2, while the methodology did not cater for other GHGs to be reported.
Undoubtedly more work is required to improve our understanding of fire impacts on peat swamp forests and to reduce uncertainties in peat fire emission estimates. Important aspects of the impact of fires, especially frequent or repeated fires, on peat such as increased peat compaction (i.e., increased peat bulk density), reduced peat carbon content, carbon redistribution from live to dead pools, production of pyrogenic carbon -or char 9, 14 are often overlooked in peatfire related estimates and are not acknowledged in recently revised IPCC guidelines 15. Moreover, highly cited publications on the amount of emissions released from peat fires in Indonesia used a simplified, non IPCC method for estimating emissions and did not distinguish between primary and degraded or cleared peatlands 5, 16.
In this study we provide an example of estimating emissions from peat fires in primary and secondary peat swamp forests and in degraded peatlands using the IPCC methodology in a transparent and accountable way. We combine data from various sources to separate emissions by fire frequencies and biomass categories (aboveground and peat). While our intention was to report emissions for all major GHGs as encouraged by the UNFCCC, the review of the literature for peat related Gi and GWP revealed that we can estimate emissions for only four major GHGs (CO2, CO, CH4 and N2O).