When waste is landfilled, organic matter is converted into landfill gas, a mixture of methane (45 to 60%) and carbon dioxide (40 to 55%). The climate effect is dominated by the methane: every kilogram of methane equals 28 kg CO₂-eq. As a result, even a limited methane flow weighs heavily in the sector balance.
A rule of thumb is that roughly 4.8 kg of methane per tonne of waste per year is formed in the first five years after landfilling, then 2.4 kg, followed by 1.3 kg in the second decade and 0.6 kg in the third. The emissions therefore correlate with the age and composition of the landfilled material, which explains why almost 800 former landfill sites continue to contribute for years. Capture and less organic waste going to landfill act precisely on this methane formation. Source: Climate Action Recap Gelderland (industry and business sector analysis), New Economy.