At the moment I'm using the Internet, as are you. In many ways, the Internet is the largest and perhaps most successful global system ever built by humanity. And yet because of the way it was built---haphazardly, over the course of a few decades---there are no maps, no records documenting its entire structure.

Given my interest in energy, and understanding how society's energy use is broken down, I wanted to understand how much energy the Internet uses. Recently my colleague Justin and I did a study to understand just that. There are many questions in addition to the obvious that we explored, including:

• Is it worth it to keep the Internet running the way we do today given future energy constraints?
• Is the Internet a large energy consumer vs. other functions of society?
• What does the Internet even consist of?

A key part of understanding the energy use of the Internet is that its embodied energy, or emergy, is important to include.

Why measure emergy?

Emergy, a concept introduced by H.T. Odum is perhaps the most ignored aspect of energy use. Loosely defined, it's the energy used to make the things that we use or buy or consume. We often ignore emergy since it doesn't directly cost us anything, so it's invisible. Nevertheless, emergy matters when we want to understand the energy-use impact of something from a society-wide perspective. As it turns out, the manufacturing of computer hardware is an extremely energy intensive process. Thus there are two important pieces to look at: the energy use of the Internet (typically viewed as the wall-socket electricity use) and the emergy of the devices themselves.

An Internet census

Before we could even consider the energy use of the Internet, we had to understand how big the Internet is in the first place. That, is, we needed to take a census. How many desktop computers are there in the Internet? How many laptops are there in the Internet? How many cloud servers are there? How many miles of fiber optics are there? How many routers are there? We were unable to find a single source that answered all of these questions. So here I'd like to provide the answers to them, along with the sources of our data. We rounded our numbers since we didn't want to convey a false sense of precision, and a few values were guesstimates because no good data was available. Also, since it's ambiguous whether some of these components are part of the Internet or not, when we include them in our final calculation we weight them with a min (lower-bound) and max (upper-bound) weight to get a range of possible energy use.

I won't go through the calculations, because they aren't particularly exciting. But the bottom line is that we calculated the wall-socket power consumption as well, and found a few interesting things:

• The embodied power---the emergy of devices divided by their replacement lifespan---is roughly equivalent to their wall-socket power consumption. That is, looking at wall-socket electricity ignores half of actual energy use for computing devices. Specifically, we estimated that the total wall-socket power use of the Internet is between 83-144 GW and the embodied power is between 87-164 GW.
• The total power use of the Internet, which we estimated to be between 170-307 GW, is about 1-2% of global energy use. We were a bit surprised by this, because we thought it might be higher than that. (Though it's a larger percentage if we were to consider electricity use alone.)
• It might be reasonable, then, to focus more attention on how the Internet can substitute for other energy-intensive societal functions. We did a simple calculation for the obvious example---transportation. Suppose we were to replace 1 out of every 4 air trips with a video conference (we assume business trips that consist of 5 one-hour meetings). Doing so would decease global energy use by about 285 GW, which is on the order of the Internet's entire energy consumption. (And the potential increase in the Internet's energy use for carrying extra video traffic would only be about 2 GW.)

The bottom line is that the few previous studies that existed were ignoring a large piece---roughly half---of the energy use in question. Despite this, it seems worth it to keep the Internet going as long as we can because it may help us, for a time, keep our energy use down. In future posts, I'd like to consider where else looking at emergy can yield insights and reveal shortsightedness.