Photo by T.P. Martins.

When I examined the reasons agriculture often gets a pass in climate negotiations recently, I pointed to the fact that precise measurement of the climate impact of many industrial farming practices remains difficult and controversial. This is especially true when it comes to synthetic nitrogen fertilizer.

The effect of excess fertilizer on our waterways gets much more attention than it does when it enters the air. And for good reason. It’s toxic to consume nitrates in your drinking water. We’re learning that agricultural overuse of fertilizer has contaminated the drinking water of whole regions of California. Meanwhile, nitrogen that runs into the ocean causes oxygen-depleted “dead zones” around the world. The dead zone in our own Gulf Of Mexico (measured every summer) keeps getting larger — last year’s was the size of New Jersey.