or How to Avoid Frightening your Readers by Hiding the Key Data Point

Occasionally I hear the argument that global warming is just part of a natural cycle; that human impact on levels of CO2 are negligible in comparison to natural shifts, and we should all just relax and keep buying SUVs. This is the kind of argument that could be quickly settled with a little data. Unfortunately arguments on global warming in the media tend to treat the issue like a tennis match, following who is scoring points over whom. I was pleasantly surprised to find an article in my excellent local broadsheet newspaper with the straightforward headline “Planet’s gas levels highest on record“. So, how much higher? Here’s the infographic:

So it looks like the headline’s overstating the case a little - the level is higher than previously seen, but not by much. There seems to be an extra graph over on the right to show more detail of the latest spike, which is much the same as all the previous CO2 spikes in the record.

Or is it? The text says:

Carbon dioxide levels are now 380 parts per million, compared with previous peaks of below about 300 parts per million.

So if our crucial data point is the number 380, why does the left-hand graph stop at 300? And hang on - that graph on the right is to the same scale on the Y axis, but it’s shifted down by 80 units. The top of the left-hand graph corresponds to a point below the middle of the right-hand graph… the data is all there, but the layout hides the one thing we’re most interested in, which is:

How much more CO2 is there now, compared with previous peaks in the record?

Let’s find out.