“Beware of people bearing growth percentages and a love of mobile connectivity, for only half the picture will often be revealed,” wrote Chris Duckett at ZDNet, channelling my almost-identical thoughts about the spin that’ll be put on the latest internet usage figures from the Australian Bureau of Statistics, released yesterday. We were right.

Predictably, most news outlets have squawked about the rise in mobile data consumption. “Mobile phone data downloads rise 43% on 2012 numbers, ABS figures show” said the ABC; “Internet downloads on mobiles in Australia surges: ABS” said StartUp Smart; and “‘Explosive growth’ in data being downloaded on phones” said the Ballina Shire Advocate and, presumably, other APN regional papers.

Now the amount of data downloaded through mobile devices has certainly risen, almost doubling over the 12 months to 30 June 2013. The amount of data downloaded through phone handsets has risen 43% in just six months.

It sounds impressive. On the surface, a standard up-and-to-the-right chart of this steady growth would seem to support the standard industry belief that more and more of our internet activity will move from fixed-line services to mobile devices, and it does.

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But to imagine that any of this supports the idea that fixed-line services are somehow obsolete, and that wireless will end up supplanting it to rule the world, is to be fundamentally ignorant of the technologies, of their relative costs, of the different data usage patterns of different online activities, of physics and of arithmetic.

The fact that wireless users share the potential bandwidth with all the other users currently on that base station has been gone through so many times that it shouldn’t need to be mentioned any more, but we do, and so I have. Same for the physics of Shannon-Hartley, which sets limits on how much bandwidth can be created in the wireless spectrum. Do we really want a wireless tower in every street?

More recently, the Centre for Energy-Efficient Telecommunications in Melbourne has modelled the internet’s energy consumption. Right now, the internet uses around 1-2% of the world’s electricity. But thanks to the proliferation of millions of energy-inefficient wireless devices, that could blow out to 10% by 2025, causing us real problems.

As recently pointed out by Mark Gregory, senior lecturer in the School of Electrical and Computer Engineering at RMIT University:

“Universities and industry research teams around the world test technologies that typically won’t come to market for 15 to 20 years. Unless there is a sudden and unexpected break-through in wireless or copper based technologies, the only known approach to provide high-speed broadband that incorporates traffic class management and Quality of Service (QoS) relies on the use of optic fibre.”

Now there’s certainly massive growth in the number of mobile internet subscriptions. They’ve outnumbered every other kind of internet subscription for more than two years now. But we need to remember that mobile devices are generally issued on a per-person basis, whereas you typically see just one fixed-line connection per household. Indeed, we’re now seeing more than one mobile subscription per person — for one or more smartphones, plus a tablet, and perhaps also a dongle for a notebook computer or a mobile wi-fi hotspot. So of course there’s more of them than fixed-line.

The killers, though, are the cost of mobile bandwidth and the minuscule data transfer allowances. As I wrote in May, there’s simply not enough to sustain a reasonable full day’s online activity.

Using 15GB per month as an example, if for no other reason than that’s the plan I’m on, it gives you half a gigabyte per day. A mere 500MB. For everything you need to do in an entire 24-hour day. It doesn’t go far.

Watching streaming video is 200-300MB/hour. An audio-only conference call on Skype is 100MB/hour. Updating your device’s operating system can be 1GB (1000MB) or more, and really needs to be done same-day to avoid security risks. Even the background chatter of staying in touch with all your cloud-based services, from email to Facebook to Twitter to Google Maps and everything else, can add up to 100MB/day, even if you’re not really doing anything.

You can certainly use mobile services for staying in touch, but fixed-line connections can, and will, be doing the heavy lifting — even if for convenience your “last-metre connection” is by wi-fi to a fixed-line internet router nearby.

If anyone reckons differently, show them this chart from ZDNet‘s Duckett, which shows quite clearly that the proportion of all data that’s coming down the wireless route is doing down, not up:

Percentage of data downloaded

As Duckett wrote:

“Mobile data may be increasing at a rapid rate, but it is yet to reach one-fifth of the data downloaded on fixed lines in December 2009. By contrast, fixed-line downloads have grown by five-and-a-half times since the end of 2009. Mobile data only makes up 2.9% of all data downloaded and rose by 0.49 percentage points. It’s hardly the sort of growth that will see mobile data get anywhere near the data downloaded by fixed broadband in our lifetimes.”