Do you prefer to own a DVD, rather than wondering if Netflix will remove whatever show you wanted to watch this week? If you buy or rent, rather than streaming, you are contributing to billions of tons of carbon going into the atmosphere.

A new paper in Environmental Research Letters claims that streaming is much better for the environment, requiring less energy and emitting less carbon dioxide (CO2), than DVD renting, buying and viewing, even when you factor in the energy cost of computers and laptops versus older DVD players. It's the driving to rent that makes a big difference, though animal activists claim that driving to rent is better for global warming than walking - if you eat meat. But they also believe milk causes autism, so don't take them too seriously.

Streaming is not carbon-free. A significant proportion of the energy consumption and carbon emissions for streaming comes from the transmission of data, which increases drastically when more complex, high-definition content is streamed.  But scholars from Lawrence Berkley National Laboratory and Northwestern University, estimated that if all DVD viewing in the US was shifted to streaming services in 2011, around 2 billion kg of CO2 emissions could have been avoided and around 30 petajoules (PJ) of energy saved—the equivalent of the amount of electricity needed to meet the demands of 200,000 US households.

What does that mean in context? Not a lot, really. That amount of emissions will be made up in 25 days of airplane flights, but if you are a person who thinks you are making a difference not running tap water while you shave, this will be a nice rationalization for doing what you already do anyway.

They estimated that in 2011, 192
of energy was used, and 10.4 billion kg of CO2 emitted, for all methods of DVD consumption and streaming in the US.

From this, they calculated that one hour of video streaming requires 7.9 megajoules (MJ) of energy, compared to as much as 12 MJ for traditional DVD viewing, and emits 0.4 kg of CO2, compared to as much as 0.71 kg of CO2 for DVD viewing.

To arrive at their results, the researchers compared video streaming with four different types of DVD consumerism: DVDs that are rented from online mailers; DVDs that are rented from a store; DVDs that are purchased online; and DVDs that are bought from a store.

Video streaming was limited to TV and movies and did not include shorter videos that are streamed online through YouTube etc.

They found that video streaming and the online rental of DVDs required similar amounts of energy; however, the renting and purchasing of DVDs from a store were much more energy intensive, due to the impact of driving.

Lead author of the research Arman Shehabi, from Lawrence Berkley National Laboratory, said, "It's a modern-day equivalent of the debate about which is more environmentally sound—the disposable or the cloth diaper.

"Our study suggests that equipment designers and policy makers should focus on improving the efficiency of end-user devices and network transmission energy to curb the energy use from future increases in video streaming. Such efficiency improvements will be particularly important in the near future, when society is expected to consume far greater quantities of streaming video content compared to today."