Given that paper accounts for a quarter of all landfill volume, it should probably come as no surprise that a recent study touted e-books as more environmentally friendly than traditional publishing. A report released this month by the San Francisco-based Cleantech Group found that Amazon’s Kindle device could generate a net savings in carbon emissions—a savings that increases as print consumption is displaced.

The study, titled The Environmental Impact of Amazon’s Kindle, called the publishing industry “one of the world’s most polluting sectors,” citing the 125 million trees felled and 153 billion gallons of wastewater produced last year by the American book and newspaper businesses. The report also said that the carbon footprint of an average book is routinely doubled when consumers drive to bookstores—a step bypassed with downloadable e-books.

According to Emma Ritch, who authored the study, the Kindle is gentler on the environment even when the consequences of its manufacturing and operation are taken into account. “The roughly 168 kg of CO2 produced throughout the Kindle’s lifecycle is a clear winner against the potential savings: 1,074 kg of CO2 if replacing three books a month for four years; and up to 26,098 kg of CO2 when used to the fullest capacity of the Kindle DX,” she wrote. “Less-frequent readers attracted by decreasing prices still can break even at 22.5 books over the life of the device.”

As the figures suggest, the study relies on the theory that Kindle owners are reducing an already higher-than-average consumption of printed matter in favor of digital substitutes. “A user that purchasers fewer than 22.5 books per year would take longer to neutralize the emissions resulting from the e-reader,” Ritch wrote, “and even longer to help reduce emissions attributed to the publishing industry.” The report also rests on the probably unrealistic assumption that users will hang on to their Kindles for a full four years before adding them to the growing accumulation of technological waste.