The Cedar Hills landfill near Seattle. Photo: King County Solid Waste Division

By Lynne Peeples, FairWarning

Next to empty shelves where toilet paper used to be is a stretch of aisle stacked with trash bags, disposable cups, and cutlery at a Whole Foods in Seattle. On the front of most of these products—in bold print—is the word “compostable,” meaning the product is biodegradable under the right conditions.

Environmentally-conscious shoppers tend to be drawn to such labels. But they might not be aware of a critical drawback: As biodegradable materials break down in a landfill, which is where they usually end up, they can release methane, a potent greenhouse gas with climate warming effects upwards of 30 times that of carbon dioxide.