Creative with bubble charts

When playing with the PBL infographics on trends in global CO2 emissions I came around some intriguing things. As seen in previous posts, PBL explained the increase in share of renewable energy by first showing the 1990 values:

Share of wind and solar increasing 1990. Source:

Share of wind and solar increasing 1990. Source:

and compare this with the 2012 values:

Share of wind and solar increasing 2012. Source:

Share of wind and solar increasing 2012. Source:

So far, so good. I found the color scheme particularly interesting. The renewable energy circle is in a deep green color and the other sources are in a pale gray. At first they seems the same gray, but looking closer that doesn’t seem to be the case. The circles of the fossil fuel group are paler than the low-carbon energy group.

The importance of this is that because of the high contrast our attention will be drawn to it and giving it more importance, especially comparing to the two other groups. Their pale colors let them fade into the background compared to the renewables group with their deep color that are now difficult to miss.

Also the renewable energy sources (wind, solar and biofuels) are lumped together to one circle while the other sources are separated into their composing elements. For low-carbon there are wood, hydro energy and nuclear. For fossil fuels there are gas, coal and oil. It is difficult to see clearly how these three groups actually compare to each other and who knows what the deconstruction of the low-carbon/fossil fuel compared to the sum of the renewables does to the perception of the graph. It would been interesting to see the three components of the renewable part as three separate circles, just as the other sources now. I guess that share would look even more insignificant than it looks now, but I don’t have that data.

The only way to compare the three groups, without the visual distractions, would be add up the values of the low-carbon & fossil fuels-groups and to give every group the same color. This is the 1990 situation:

Share of energy per group

Share of Energy per group 1990

The same for the 2012 situation:

Share of energy per group 2012

Share of Energy per group 2012

Now you could say that it isn’t not really that bad, that the circle of the renewable energy is not that small. It is not impressive, but not bad either considering where it came from. That was what I was thinking also, even when knowing the percentages. The problem is perception of the area in graphs. Circles have the nasty habit that the perceived size divert from the actual size when they are scaled. While people are good at estimating lengths correctly, we are really lousy at estimating area.

Research done on this subject has shown that most people systematically under-estimate differences in area. This tendency gets worse when the difference gets larger. Not convinced? Just try to guess exactly how many times the renewable energy circle fits into the two other circles and you will get the drift. With no values and a vague double reference, the graph seem to be deliciously vague.

Hey, they obviously didn’t want to show something like this:

Bar graph energy per group - difference 1990 - 2012

Bar graph share of energy per group | difference 1990 – 2012

This is the same data, only presented as a bar graph. Here we see clearly the proportion of the different groups in a linear way, which we are able to estimate correctly. This shows how tiny the share of renewable energy is and it would reveal that their claim that renewables have a significant influence on the “decrease” of emissions is just bogus.


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