One tag, two meanings: the unit problem in India's first machine-readable climate filings

What we found

Each XBRL fact carries a machine-readable unit reference. Read literally, 18 of the 22 MtCO2e figures are physically impossible — several would individually exceed global annual emissions. Checking every flagged company against the units stated in its own PDF filing:

• 21 companies confirmed mistagged — their PDFs state "Metric tonnes of CO2 equivalent" for the same figures the XBRL tags as megatonnes. Eight match digit-for-digit (Dr Reddy's 1,16,841; ONGC 8,379,783.82; BEL 8,109.76; IndiGo 10,419,376.30; Jio Financial 1.73; Apollo Hospitals 13,167.90; Eternal 25.62 — matched in both the current and prior year; UltraTech Cement 8,88,84,246, one of India's largest emitters), and Coal India matches exactly as the sum of the two entity-level tables in its PDF.
• 1 company confirmed correct — Tata Steel's MtCO2e-tagged values are genuine megatonnes: its prior-year Scope 3 of 23 MtCO2e matches the 23 Mt figure in its FY2024-25 PDF.

The precise defect is therefore not a wrong unit — it is an unreliable unit field. The identical tag carries tonnes for most filers and megatonnes for one. No consumer of this data — researcher, data vendor, or index provider — can normalize it by trusting the tag.

This is not a Nifty-50 quirk — it runs across the whole first vintage

We then read the Scope 1 unit tag on every FY2025-26 BRSR filing in the exchange window — 768 companies, not just the fifty largest. The pattern is not confined to big caps; it is systemic.

The population census is deterministic — it only reads the tag; it makes no judgement. The conclusion that these MtCO2e values are really tonnes rests on the PDF checks, which we extended beyond the Nifty 50 and which keep holding: Hindustan Zinc's PDF states "Metric tonnes of CO2 equivalent" for a Scope 1 of 47,82,041 — exactly its XBRL value tagged MtCO2e; Tata Chemicals' PDF reads 48,50,029, again digit-for-digit. Across every one of the 24 companies checked against their own PDFs — spanning cement, metals, power, banking, pharma and IT — the MtCO2e-tagged figure is tonnes, the sole exception being Tata Steel's genuine megatonnes. The 169 smaller MtCO2e values that are not magnitude-impossible are left unclaimed; only the deterministic census and the PDF-verified sample are asserted here.

Likely mechanism

ONGC's own PDF labels its emissions unit "MTCO2e." In greenhouse-gas accounting convention, "MT" reads metric tonnes; a filing tool mapping the abbreviation to the taxonomy's megatonnes unit would produce exactly the pattern observed — a shared software-side misreading rather than 21 independent data-entry errors. We flag this as a plausible mechanism, not an established fact.

Why it matters

This is the first machine-readable vintage of Indian corporate climate data. Whatever consumes it downstream inherits the error unless it re-verifies every company by hand — which removes the point of machine-readability. It is also fixable at the source: one validation rule in the filing utility would catch essentially every instance at filing time. And in every verified case the number matches the company's PDF — this is a metadata defect, not misreporting. No company is accused of misstating its emissions.

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