The Himalaya has long been regarded as a carbon sink; recent research suggests otherwise in certain contexts. Critically analyse.

Chemical weathering of freshly exposed silicate rock consumes atmospheric CO₂ and locks it as bicarbonate in marine sediments — a mechanism credited with cooling Earth since the Himalayan orogeny began with the India–Eurasia collision. Recent isotopic work on the Indus headwaters shows this sink view is valid only partially, and reverses in rapidly eroding glaciated terrain.

The case for the Himalaya as a carbon sink

• Steep relief and high erosion continuously expose fresh silicate minerals, sustaining CO₂ drawdown of roughly 1.4 × 10⁵ mol/km²/year in the upper Indus basin [1].
• The floodplain reaches of the basin remain a net CO₂ sink, confirming the classical model holds downstream [1].
• Silicate weathering estimates elsewhere in the basin still show substantial CO₂ consumption, retaining the Himalaya's global climatic significance [2].

The counter-evidence: a hidden geological CO₂ source

• Himalayan rock carries pyrite (FeS₂, "fool's gold"); erosion exposes long-buried sulphides, which oxidise to sulphuric acid that dissolves carbonate rock and releases CO₂ [1].
• Dual-isotope tracing (δ³⁴S and δ¹⁸O) of dissolved sulphate attributes a large majority of upper-basin sulphate to pyrite oxidation, releasing about 4.4 × 10⁵ mol CO₂/km²/year — roughly three times the silicate drawdown, making the headwaters a net source [1].
• Accounting for pyrite lowered estimated CO₂ consumption in the basin to about 80% of conventional estimates [2].
• Taiwan's shale catchments showed the same co-variation, with fast-eroding terrain emitting CO₂ about twice as fast as slow terrain sequesters it [3].

Assessment: the sink-source balance is scale- and zone-dependent, not a single verdict. Yet the emissions operate over geological timescales and cannot explain present anthropogenic warming.

The Himalaya is best read not as a fixed sink but as a dynamic carbon regulator whose sign shifts with erosion rate and glacial cover. As glacial retreat accelerates, refining carbon-budget models and strengthening Himalayan monitoring under the National Mission for Sustaining the Himalayan Ecosystem [4] will keep climate projections — and SDG 13 action — grounded in evidence.