全球变化知识资源中心

To the Editor —

Palm oil production is driving economic growth, rural development and poverty alleviation in many equatorial economies, yet often with loss of tropical forests¹. Here we show that the climate threats do not end following forest clearing: methane (CH₄) emissions from palm oil wastewater effluent, known as POME², represent a significant and rising source of atmospheric warming.

A typical wastewater facility emits around 3,288 tCH₄ yr⁻¹, equating to 111,804 tCO₂e yr⁻¹ because of the greater global warming potential of CH₄ (Supplementary Tables 1–3 and Excel database) — comparable to the annual emissions of ~22,000 passenger vehicles in the United States³. This year, emissions will reach ~135 MtCO₂e yr⁻¹ pantropically (Fig. 1), equal to over 30% of Indonesian fossil fuel emissions⁴. Projections of industry growth⁵ suggest emissions could rise to 0.363 gigatons of CO₂e yr⁻¹ by 2050, which is roughly 12% of gross carbon emissions from tropical deforestation⁶, or 1% of current global greenhouse gas emissions from fossil fuel and cement production⁴ — a large climate impact that remains insufficiently addressed within the public debate over the sustainability of the industry.

Global scale CH₄ emissions and electricity potential were calculated by applying CH₄ emission and energy scaling factors to palm oil production statistics (Supplementary Tables 1–4 and Excel database). Error bars reflect the uncertainty in CH₄ emissions at 95% confidence intervals based on potential variation in wastewater treatment conditions at mills throughout the tropics (Supplementary Table 4). We estimate that 5% of mills capture POME bioenergy pantropically (shaded portion).