Tony Cenicola/The New York Times

A new study analyzing the Amazon Kindle electronic book reader’s impact on the environment suggests that, on average, the carbon emitted over the life of the device is offset after the first year of use.

“It’s not just buying e-books that matters,” said the report’s author, Emma Ritch, of San Francisco-based Cleantech Group. “The key is they displace the purchase of 22.5 physical books.” Ms. Ritch said.

“The new study finds that e-readers could have a major impact on improving the sustainability and environmental impact on the publishing industry, one of the world’s most polluting sectors,” a statement at Cleantech’s Web site states. “In 2008, the U.S. book and newspaper industries combined resulted in the harvesting of 125 million trees, not to mention wastewater that was produced or its massive carbon footprint.”

The report asserts that printed books have the highest per-unit carbon footprint — which includes its raw materials, paper production, printing, shipping, and disposal — in the publishing sector. “In the case of a book bought at a bookstore,” Ms. Ritch said, Cleantech’s measurement “takes into account the fossil fuels necessary to deliver to the bookstore and the fact that 25-36 percent of those books are then returned to the publisher, burning more fossil fuels.”

After that, Ms. Ritch said, there are three common next steps: “The publisher then incinerates, throws away or recycles them,” she said.

According to Sarah Rotman Epps, a media analyst with Forrester Research in Cambridge, Mass., which supplied some of the data for the report, first-quarter e-book sales in 2009 accounted for a scant 1.6 percent, or $113 million in revenue, in the $24.3 billion publishing industry. “Right now, e-books are having effectively no positive impact on the environment,” she said, nor will they “unless publishers print fewer books in anticipation of e-book sales.”

The Association of American Publishers reported sales of e-books were up 154.8 percent by the end of April 2009, while overall book sales were down 4.1 percent; 2008 e-book sales totaled $112 million, and some analysts predict sales may reach $400 million in 2012.

By the end of 2008, sales of e-book readers like the Kindle and Sony’s Reader reached approximately 1 million units, while Apple reported more than 1 million downloads of Amazon’s free Kindle e-book reader application for the iPhone.

The Cleantech study concluded that purchasing three e-books per month for four years produces roughly 168 kilograms of CO2 throughout the Kindle’s lifecycle, compared to the estimated 1,074 kilograms of CO2 produced by the same number of printed books.

Of course, none of this means that e-readers are without environmental impact. Consumer electronics, after all, are notorious for containing a variety of toxic materials among their circuitry. Valerie Motis, a Sony spokeswoman, said in an e-mail message that the company’s e-reader products are free of toxic materials, including polyvinyl chloride, or PVC — a particular bugaboo among environmental groups.

Phone calls and e-mail messages to Amazon inquiring about the materials in the popular Kindle device have thus far gone unanswered.

Casey Harrell, an international campaign coordinator for Greenpeace, which monitors the environmental impact of consumer electronics, said e-readers remain something of an unknown variable.

“In terms of the Kindle or other similar e-book gadgets, I don’t know what chemicals are in or out,” Mr. Harrell said. “Companies will want to brag about their eco-credentials, so if you don’t see any mention, they’ve probably not been eliminated.”

Mr. Harrell suggested another option for those concerned about the environmental footprint of books: “There’s always the public library,” he said.