A tale of two charts

Is the glass half full or three-quarters empty?

This week’s Economist story on China’s continued reliance on coal, even as its growth in use of renewables leads the world, painted a balanced picture of the subject, as you’d expect. One picture used to illustrate it, however, was less than balanced. While just one of three images used in the article (the others were a photo and a map), it’s a fine example of the power of statistical graphics to lead an audience in a particular direction. Here it is:

By presenting the energy sources of China’s electricity production as a percentage share, the graph suggests that coal, while not on the way out of China’s energy mix, is on its way down. It also shows how the share of cleaner energy if growing.

Good news, right?

Yes, up to a point. That point is better illustrated if you compare the percentage share versus the absolute amount for each of the same sources over the same time period.

Here’s the same data, from the same source, presented side by side for ease of comparison (with apologies for a level of illegibility that the Economist’s graphics department would never stand for):

The difference is clear. While coal’s share of China’s electricity production is indeed falling, the absolute amount of coal being used to generate the electricity that’s helping to power China’s growth is inexorably increasing, even accounting for increases in how efficiently coal is burned. Since climate change is caused by absolute levels of greenhouse gas emissions, it’s the latter view that is most relevant to the story. And it’s not a reason to be cheerful.

The Economist is far from alone in erring towards percentage share data in its graphics (and it should be said that the article itself is clearer on the absolute picture). Many climate campaigners proudly – and justifiably, but again only up to a point – use the same approach to convince their audiences that renewables are now mainstream and unstoppable.

It’s fine for the glass to be half full, but dangerous to choose graphics that risk an overly rosy conclusion. Because now, more than ever, we need to be clear that much, much more clean energy is needed.

One reason is the simple fact that electricity is not the same as energy. While climate economists and campaigners generally keep in mind that electricity is only a relatively small part in any major country’s total energy mix, the person in the street is less well informed. Indeed, I myself – a tedious obsessive about this subject –mistake the two far too frequently.

The fact is that electricity makes up less than 20% of the world’s energy. Even in China, which has made itself a leader in electrification, it’s still less than a quarter. Since almost all renewables go towards electricity generation, the rest is fossil fuels.

That glass is unquestionably three quarters empty.