POTENT EMITTER

Termites are a major source of methane, but determining the risk they pose to global warming is fraught with uncertainty

- ROHINI KRISHNAMURTHY

IN VIRTUALLY every tropical forest, grassland or warm, humid and wooded area around the world, one can see porous castles, 2-5 m tall and made of soil, water and saliva of their habitants, termites. These small insects, who live in the mounds as colonies of 60,000-200,000, are not just skilled architects and engineers but also a surprising source of methane, a greenhouse gas more potent than carbon dioxide.

Termites are counted among natural sources of methane like wetlands, wild animals, livestock and geological features like volcanoes, and are estimated to account for 1-3 per cent of emissions globally. In 2008-17, the world emitted 576 Tg (1 Tg or teragram is equal to 1012 g) of methane per year, of which termites contributed 9 Tg, says the Global Carbon Project, in its “Global Methane Budget” published in 2020. Other estimates put the emissions at 2-15 Tg per year.

However, scientists say actual emissions could be greater or lesser than these estimates. To establish certainty, there is a need to understand the relationship between termite colonies and methane.

Termites are known to wreak havoc on agriculture, forests and construction, due to their affinity for plants and wood. However, only 10-15 per cent of 3,000 termite species identified globally are categorised as pests. In natural ecosystems, they feed on and recycle the nutrients present in dead and decaying plant and animal matter. It is this cellulose-rich diet that causes their emissions. Methanogenic microorganisms that live in the gut of termites break down the cellulose entering the body and release methane.