With e-readers like Apple’s new iPad and Amazon’s Kindle touting their vast libraries of digital titles, some bookworms are bound to wonder if tomes-on-paper will one day become quaint relics. But the question also arises, which is more environmentally friendly: an e-reader or an old-fashioned book?

To find the answer, we turned to life-cycle assessment, which evaluates the ecological impact of any product, at every stage of its existence, from the first tree cut down for paper to the day that hardcover decomposes in the dump. With this method, we can determine the greenest way to read.

(A note about e-readers: some technical details — for instance, how those special screens are manufactured — are not publicly available and these products vary in their exact composition. We’ve based our estimates on a composite derived from available information. It’s also important to keep in mind that we’re focusing on the e-reader aspect of these devices, not any other functions they may offer.)

One e-reader requires the extraction of 33 pounds of minerals. That includes trace amounts of exotic metals like columbite-tantalite, often mined in war-torn regions of Africa. But it’s mostly sand and gravel to build landfills; they hold all the waste from manufacturing wafer boards for the integrated circuits. An e-reader also requires 79 gallons of water to produce its batteries and printed wiring boards, and in refining metals like the gold used in trace quantities in the circuits. A book made with recycled paper consumes about two-thirds of a pound of minerals. (Here again, the greatest mineral use is actually gravel, mainly for the roads used to transport materials throughout the supply chain.) And it requires just 2 gallons of water to make the pulp slurry that is then pressed and heat-dried to make paper. Fossil Fuels The e-reader’s manufacture, along a vast supply chain of consumer electronics, is relatively energy-hungry, using 100 kilowatt hours of fossil fuels and resulting in 66 pounds of carbon dioxide. For a single book, which, recycled or not, requires energy to form and dry the sheets, it’s just two kilowatt hours, and 100 times fewer greenhouse gases. Health The unit for comparison here is a “disability adjusted life-year,” the length of time someone loses to disability because of exposure to, say, toxic material released into the air, water and soil, anywhere along the line. For both the book and the e-reader, the main health impacts come from particulate emissions like nitrogen and sulfur oxides, which travel deep into our lungs, worsening asthma and chronic coughing and increasing the risk of premature death. The adverse health impacts from making one e-reader are estimated to be 70 times greater than those from making a single book. If you order a book online and have it shipped 500 miles by air, that creates roughly the same pollution and waste as making the book in the first place. Driving five miles to the bookstore and back causes about 10 times the pollution and resource depletion as producing it. You’d need to drive to a store 300 miles away to create the equivalent in toxic impacts on health of making one e-reader — but you might do that and more if you drive to the mall every time you buy a new book. If you like to read a book in bed at night for an hour or two, the light bulb will use more energy than it takes to charge an e-reader, which has a highly energy-efficient screen. But if you read in daylight, the advantage tips to a book. If your e-reader ends up being “recycled” illegally so that workers, including children, in developing countries dismantle it by hand, they will be exposed to a range of toxic substances. If it goes through state-of-the-art procedures — for example, high-temperature incineration with the best emissions controls and metals recovery — the “disability adjusted life-year” count will be far less for workers. If your book ends up in a landfill, its decomposition generates double the global warming emissions and toxic impacts on local water systems as its manufacture.