Draining peatlands for agriculture adds 'huge pulse' to global warming

New research has calculated the damage done by farmers converting tropical peat swamps to oil palm plantations.

The findings published today in Nature Communications provide the first evidence of the significant pulse in greenhouse gas emissions released by the practice.

Tropical peat swamp forests hold around 20% of global peatland carbon. However, the contribution of peat swamp forests to carbon storage is currently under threat from large-scale expansion of agriculture including oil palm and pulp wood production.

Draining peatlands increases the oxygen levels in the soil, which in turn increases the rate of decomposition of organic material, resulting in high CO2 emissions from drained peatlands. In addition to CO2, peatlands also emit the powerful greenhouse gases (CH4 and N2O8)..

Much more carbon

Study co-author Dr Stephanie Evers, from the School of Biological & Environmental Sciences at Liverpool John Moores University, explained: “These peat swamp forests store much more carbon then normal tropical rainforests but with drainage and land use conversion, they become globally significant sources of carbon to the atmosphere.”

In fact, the new data suggests that conversion of peatlands to oil palm is responsible for between 16.6 and 27.9% of combined total national greenhouse gas emissions from Malaysia and Indonesia or between 0.44 and 0.74% of annual global emissions.

“Clearly, sustainable management of these unique ecosystems is really important to help control global greenhouse gas emissions and resulting climate change,” added Stephie.

The study led by plant scientists at the University of Nottingham is the first to examine the three main greenhouse gas emissions across the different age stages of palm oil plantations, and was carried out in the North Selangor peat swamp forest in Malaysia with support from the Salangor State Forestry Department.

Demand tripled

Palm oil is the most consumed and widely traded vegetable oil in the world. Global demand has more than tripled in the last eighteen years, from around 20 million tonnes in 2000 to over 70 million in 2018 and Malaysia is the world's second largest producer.

Five sites were analysed at four different stages of land use: secondary forest, recently drained but uncleared forest, cleared and recently planted young oil palm plantation and mature oil palm plantation.

Laboratory analysis of soil and gas from these sites showed that the greatest fluxes of CO2 occurred during the drainage and young oil palm stages with 50% more greenhouse gas emissions than the mature oil palms. These emissions also account for almost a quarter of the total greenhouse emissions for the region.

Dr Sofie Sjogersten from the University of Nottingham's School of Biosciences said: "Tropical peat swamps have historically been avoided by palm oil growers due to the amount of preparation and drainage the land needs, but as land becomes more scarce there has been an increased demand to convert sites and the periphery of North Selangor is being heavily encroached upon by palm oil plantations.

"Our research shows that this conversion comes at a heavy cost to the environment with greater carbon and greenhouse gas emissions being caused by the early stages of the growth of palm oil."