Technology changes everything, but it seems to change music the most. Four or five generations of recorded music technology have passed in my lifetime. As a child, I listened to Marlo Thomas’s “Free to Be You and Me” on vinyl. During middle school, I bought Rob Base and DJ E-Z Rock on cassette. Then came Pearl Jam on compact disc, followed by MP3 files purchased over the Internet.

The most recent turn of the wheel? Music is free. And why shouldn’t it be? Digital music is merely information, and information wants to be free, right? Services such as Pandora and Spotify allow people to stream digital music anytime, anywhere, as long as they have a data connection.

But what does free, unlimited streaming music means for the environment? As with so many environmental questions, the answer is complicated.

Digital music seems intuitively better for the environment than physical formats. CDs, cassettes and albums are all made of plastic and metal, the raw ingredients of which have to be extracted from the ground and molded into shape. Unlike digital music, they require packaging. (Older readers may remember the early 1990s: compact disc packaging, plastic jewel cases, plastic wrap and long cardboard boxes.) Pollution-belching trucks deliver CDs, records and tapes to the store or your home.

These impacts are all important, but let’s not focus solely on physical material. It’s a trap we all fall into sometimes. You may reject disposable cups or scold fast-food cashiers who hand out three-inch stacks of napkins. But how many times have you passed up the opportunity to watch a YouTube video on environmental grounds?

Even though they’re difficult to see or touch, the environmental impacts of streaming data are real. Digital files don’t really live in the “cloud”: They live on physical servers in massive warehouses scattered all over the world. Those machines have parts, and those parts get hot. Internet companies consume incredible amounts of energy running their servers and cooling them off. In late 2011, Google disclosed that its servers continuously use around 260 megawatts of electricity, which means one-quarter of a typical nuclear power plant’s output could be continuously dedicated to Google’s servers alone.

Data also need a way to get from these server farms to your home, and that means more servers and routers, each using power, passing it over the network. And, as the amount of data traveling over the Internet grows, more hardware will have to be built to sustain it, using even more energy. Streaming entertainment represents an enormous portion of the Internet’s total energy usage. According to data released by the computing giant Cisco, video accounts for about half of the traffic on the Internet.

Music is less data-intensive than video, but the energy requirements are calculable. Looking at the power used by servers and routers that host the music and deliver it to your personal device, Norwegian engineer Dagfinn Bach estimated that streaming an album (or the equivalent number of songs) 27 times can require approximately the same amount of energy as producing and shipping a CD to a consumer.

That simple number, 27, provides a useful starting point. If you plan to listen to a song dozens of times, it might be slightly greener to buy the CD or download the MP3 file once than to stream it over the Internet again and again. But the situation is more complex. Streaming audio — particularly the free-of-charge variety that is so popular right now — fundamentally changes our listening habits. With Spotify, for example, the average person went from having a few thousand songs of his or her careful choosing on a hard drive to more than 20 million available online. We used to listen to a few songs repeatedly. Now we can listen to more songs, with fewer repetitions. In this way, streaming audio helps make its own environmental case: If we’re now expecting to listen to thousands of different songs, it’s environmentally inefficient to have each of them delivered to us either on CD or by computer download.

In addition, you probably don’t know when you first hear a song whether you’ll listen to it 27 times or not. Some songs are ear worms, while others are to be enjoyed a couple of times, then forgotten.

The take-home message, though, is that music streaming and cloud computing do have impacts on the Earth, even if you’re not quite aware of them. But instead of worrying about choosing between CDs and streaming, think about waste, just as you worry about wasting napkins or gasoline. Ask yourself: Do you really need to stream “Thrift Shop” into your home for the 28th time? Maybe it’s time to download it. Or do the Earth and your neighbors a favor, and cut yourself off and enjoy a little peace and quiet.

There may be a greener musical future. In his report, Bach mentions Moore’s Law, which essentially predicts that the amount of data we can store on a computer chip doubles every year. That means, in the not distant future, it will be possible to include every song ever recorded on a small chip inside your phone or computer. The catalogue could be password-protected so that when you wanted access to more songs, you’d simply buy a code to type in and more songs would become available. (Some video games sort of work this way: You get a code to unlock more levels after you’ve met certain goals.) And then rather than streaming huge amounts of data, all that will pass over the Internet would be the few characters in the code.