Thread by @washingtonpost

In the foothills of the Sierra Madre mountains, the carcasses of starving cattle rotted in a bone-dry reservoir.

Down on the valley floor, farmworker Rafael Parra bent to the work of feeding the world — and unintentionally warming it. wapo.st/3mmTaWk

Parra plunged one end of an old, plastic tube into an irrigation canal, generating the suction that sent water gurgling into the drought-parched earth.

“That’s all there is to it.”

He was not fully aware of the invisible consequences of his work. wapo.st/3mmTaWk

Scientists who have studied this valley for decades know that it’s at these precise conditions — when water mixes with nitrogen fertilizer, with no crops in the ground to absorb it — that huge surges of nitrous oxide gas are released into the atmosphere. wapo.st/3mmTaWk

The world’s climate conferences and pledges have done nothing to change a basic and dangerous fact: Concentrations of major greenhouse gases in the atmosphere continue to rise. wapo.st/3mmTaWk

What happens each fall in this valley underscores how difficult it is to even track these emissions accurately, let alone stop them. wapo.st/3mmTaWk

Emerging scientific evidence suggests that Mexico’s emissions of nitrous oxide are significantly underestimated — emissions may be double or even quadruple what the country reports.

It’s a problem that the Mexican government acknowledged to The Post. wapo.st/3mmTaWk

Without regulation, the fight against nitrous oxide pollution is left to people such as Iván Ortiz-Monasterio, a 63-year-old agronomist from Cuernavaca who has spent his career trying to convince farmers to use nitrogen more efficiently. wapo.st/3mmTaWk

In the fourth installment of our series, Invisible, The Washington Post examines how over-fertilization in Mexico results in a surge of nitrous gas that scientists and the government are grappling to understand. wapo.st/3mmTaWk