A paper published April 14 in Nature Cities, using satellite retrievals and ground-based flux measurements across 450 municipalities, finds that cities account for roughly 10 percent of global human-caused methane emissions — about three times what official greenhouse-gas inventories have claimed for at least a decade. [1] Livestock concentrated at urban fringes and municipal sewer systems drove most of the underreporting; industrial sources had been counted reasonably well. [2]

The finding pairs with February's MethaneSAT work on the Permian Basin, which measured oil-and-gas methane emissions at roughly four times what the Environmental Protection Agency's inventory reported. [3] Two different satellite regimes have now produced the same indictment against two different sectors of the official accounting: the number the world is trying to reduce is smaller on paper than in the air. The urban variant is, in policy terms, the worse of the two — cities are where most countries have staked their 2030 commitments, and where the mitigation investment has been priced against the bad inventory.

The methodological story is that ground-truth satellite data has finally caught up with the bottom-up counts that regulators have relied on. [4] The political story is that every municipal climate plan written since 2015 has, in varying degrees, used a denominator that is a third of the real one. New York, London, São Paulo, Jakarta — each will need to re-cost a target or re-phrase a commitment. Livestock and sewers are not photogenic; the lack of photogenic targets is why they were the ones the inventory missed.

Ed Yong's physics lesson applies here too: reality is measured, not declared. The policy architecture that declared it ten years ago is now an outdated instrument.

-- DARA OSEI, London