Emission-factor accuracy benchmark

How wrong are language models when you ask them for an emission factor with no tools — and, worse, how often do they name the wrong source for a number?

467 questions, 45 sections, 75 publishers, generated deterministically (seed 20260910) from data version 2026.187. Only factors we may republish are used, so the answer key ships with the benchmark.

Questions are phrased the way a practitioner asks, not as canonical keys:

What is the greenhouse-gas emission factor for UK grid electricity — location-based, per kWh?

What is measured

Metric	Why it matters
answered / declined	does it give a number at all
within_10pct	is the number right
cited	did it name a publisher
citation_correct	is the source it named the source the number comes from
confidently_wrong	gave a number, off by >50%, no hedge

The fourth row is the story. A model that cites DEFRA for an EPA figure is more dangerous than one that cites nothing, because the citation is what makes a reader stop checking.

The write-up lives at greencalculus.com/guides/ai-emission-factors-accuracy — the findings, the caveats and a live factor lookup you can try. This repo is the evidence behind it: the questions, the answer key, every model's raw output, the scoring code and the harness, so anyone can re-run it and check us.

Licence terms for all 137 sources: emission-factor-licences.

Result — five models, 467 questions, no tools

Model	Answered	Right when it answered	Right of all 467	Right source, wrong number
Gemini 3.1 Pro	77	65.2%	6.4%	35.3%
Grok 4.6	144	62.1%	8.8%	31.6%
GPT-5.5	326	58.2%	31.9%	41.0%
Claude Opus 5	430	46.2%	31.0%	53.1%
Gemini 3.6 Flash	404	42.7%	28.1%	58.0%

Those middle columns rank in opposite orders. The more a model answers, the less each answer is worth — the last column sorts with talkativeness.

One vendor, two tiers, no cross-vendor argument: Gemini Pro answers 77 questions at 65.2%; Gemini Flash answers 404 at 42.7% — and the fast tier, the one that actually gets deployed behind a production pipeline, is wrong about the number more often than not even when it names the right publisher.

…and connecting GreenCalculus fixes it

90 questions, paired, same model with and without two keyless lookup tools:

	Without tools	With GreenCalculus
Claude Opus 5 — within 10%	38.1%	98.7%
Claude Opus 5 — off by >50%	23.8%	1.3%
GPT-5.5 — within 10%	50.0%	100.0%
GPT-5.5 — off by >50%	19.6%	0.0%

About +61 points for both, at 1.0–1.6 tool calls per question. The model is not handed the answer — it searches, picks the factor and reads the value, so this measures the integration, not a rigged prompt.

Full write-up, caveats, and the log of the scorer's own eight bugs: FINDINGS.md.

A second study: who AI recommends

aeo/ is a separate measurement in the same spirit. The benchmark above asks whether AI gets emission factors right. The AEO arm asks whether AI knows who sells them: 25 buying prompts across six intents, put to the same five models with no tools and no web access, 125 answers, every vendor mention counted.

Climatiq leads at 69% reach and 43% first-named, then ecoinvent (68%) and EXIOBASE (58%); 93% of answers name one of those three. Public datasets outrank every vendor — DEFRA and the US EPA at 83% each. GreenCalculus, who ran the study, was named in 0 of 125 answers, one of only two tracked vendors never named at all.

It also contains a direct probe: asked about GreenCalculus with explicit permission to decline, every model that answered declined. Asked instead to compare us to Climatiq, two of four invented a company profile. Write-up: https://greencalculus.com/guides/ai-recommended-carbon-data-providers/

Status

Everything above has been run. Nothing here is a projection.

• All five models, all 467 questions, unaided — Claude Opus 5, GPT-5.5, Gemini 3.1 Pro, Gemini 3.6 Flash, Grok 4.6. Raw replies are in results/, one directory per model, so any number in this README can be re-scored from the answers that produced it.
• The paired tool run — 90 questions, two models, with and without the two keyless lookup tools (results/paired.json).
• build_questions.py — generates questions.json. Run and verified.
• score.py — scoring and summary. Verified against 8 synthetic answers covering exact, close-but-wrong-source, confidently wrong, refusal, and a bare year (which must not be read as a value). Does unit reconciliation (units.py) and unit-aware, range-aware extraction; validated against independent hand adjudication of the pilot — automated 46.9% vs hand-read ~47%.

Two bugs found in our own harness, both fixed, both worth knowing about:

• A refusal that name-drops a publisher ("consult the DEFRA tables") was counting as a correct citation. Citations now only count on answers that actually gave a number.
• questions.json was published with 6 duplicate rows — the section listing the API serves can repeat a key, and the generator's dedup arrived one commit after the file. Scoring keys on the factor key, so the duplicates always collapsed and no published result changes; the file now says 467 like everything else. Six more, all in unit handling, are logged in FINDINGS.md.

Run

python3 build_questions.py                   # regenerate the set
python3 score.py runs.json questions.json    # score a model's answers

runs.json is [{"id": "<factor key>", "answer": "<the model's raw reply>"}] — so any model or harness can produce it.

Contamination, and the part of this benchmark that is not published

A benchmark measures a model only while its answer key sits outside that model's training data. questions.json — 467 questions with their answers — has been public since 10 September 2026, so it must be assumed reachable by any model trained after that date. A high score from such a model may be memory, not knowledge, and nothing in the file can tell the two apart.

Two things address that.

A canary. A GUID that appears nowhere else is embedded in questions.json itself, so it travels with the data even if that one file is scraped alone. Ask a model to complete canary GUID with no web access: if it reproduces ours, it was trained on this repository and its score here is not a measurement. See CANARY.md.

A pre-registered held-out split. 136 further questions across 34 sections and 47 publishers, drawn by the same generator from the same corpus, disjoint from the public set by construction (the generator excludes every published id, not merely a different seed) and never published.

The set itself is not in this repository. What is committed is holdout-manifest.json: its size, section spread, publisher spread, seed and the SHA-256 of the held-out file. That is a pre-registration — it fixes the shape and the hash in public, in advance, so that if the set is ever released it can be verified as the same one. No quiet swap after seeing which questions a model got wrong.

python3 build_questions.py --holdout   # regenerates it; writes the manifest

How to read every result from here on. We report two numbers per model: the public split and the held-out split. If they agree, the public score is measuring knowledge. If a model scores materially better on the public split, the gap is memorisation, and we will report it as such rather than as accuracy.

A CI job fails the build if holdout.json ever becomes tracked, if the manifest starts carrying contents, or if the canary goes missing or disagrees with CANARY.md.

The AEO study is the opposite case. aeo/ measures which vendors models name unprompted. There is no answer key to protect, and contamination there does not corrupt a measurement — it is the thing being measured. No held-out set applies.

Loading it

The whole thing is on the HuggingFace Hub as five configs — no auth, one line:

from datasets import load_dataset

answers = load_dataset("greencalculus/emission-factor-benchmark", "answers")   # 2,335 scored replies
paired  = load_dataset("greencalculus/emission-factor-benchmark", "paired")    # with/without a lookup tool

Config	Rows	What it is
answers	2,335	Every model's reply to every question, scored
questions	467	The instrument: question, truth value, unit, publisher, source cell
paired	360	90 questions × 2 models × with/without a sourced lookup
recommendations	125	25 buying prompts × 5 models, vendors named annotated
direct_probe	12	What a model does when asked about a vendor it has no data on

Built by hf/build.py, whose scored columns come from the same score_one() as every published figure — so the Hub copy cannot drift from this repo. It refuses to run without the held-out set available to check against, and hf/push.py re-checks every row before uploading.

A related tool: gwp-basis-check

This benchmark measures whether a model recalls the right number. A neighbouring question is whether the software people already use recalls the right report.

gwp-basis-check finds greenhouse-gas warming-potential tables that contradict the IPCC assessment report they name — a field called ar5 holding AR4's value for that gas. It is deliberately not a staleness check: AR4 and AR5 values are frequently correct, because the EU F-Gas Regulation mandates AR4 and DEFRA and UNFCCC reporting use AR5.

It came out of an audit of our own corpus, which found 66 wrong cells out of 407 checked. MIT, no dependencies, and it does not go stale — the assessment reports it rests on are closed.

Errata

7 October 2026 — one answer-key value corrected. The truth value for food.diet.mixed.annual (mixed / medium meat-eater diet, Scarborough et al. 2023, Nature Food) was 2,733.85 kg CO2e per person per year, built from 7.49 kg CO2e a day. The paper's Table 3 gives 7.04 kg a day, so the value is now 2,569.6. The six diet rows also now carry gwp_set AR6_100, the basis the paper states. The error came from the GreenCalculus MasterBrain, which was corrected the same day (v2026.239).

No published figure changes. Three models' answers to this question are now closer to the truth but stay on the same side of the 10% and 50% thresholds, and the with-tools answers stay within 10%. python3 verify/figures.py gives identical output before and after the fix, and --check-fresh passes. The HuggingFace dataset has been rebuilt with the corrected value; the Zenodo v1.0.0 deposit is a frozen snapshot and still carries the old one.

Citing this benchmark

Archived on Zenodo. The concept DOI always resolves to the latest version; cite the versioned DOI if you need the exact snapshot you ran against.

• Concept DOI (latest): 10.5281/zenodo.22692277
• Version 1.0.0 (10 Sep 2026): 10.5281/zenodo.22692278

Say, J. (2026). GreenCalculus Emission-Factor Accuracy Benchmark (with the AI vendor-recommendation study) (Version 1.0.0) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.22692278

Machine-readable metadata is in CITATION.cff.