After the Paul Nurse programme the other day, eyebrows were raised over one of the claims in the show, namely that emissions from fossil fuel burning dwarfed natural emissions. Here's an excerpt from the transcript:
Bob Bindschadler: We know how much fossil fuel we take out of the ground. We know how much we sell. We know how much we burn. And that is a huge amount of carbon dioxide. It's about seven gigatons per year right now.
Paul Nurse: And is that enough to explain...?
Bob Bindschadler: Natural causes only can produce - yes, there are volcanoes popping off and things like that, and coming out of the ocean, only about one gigaton per year. So there's just no question that human activity is producing a massively large proportion of the carbon dioxide.
Paul Nurse: So seven times more.
Bob Bindschadler: That's right.
Aynsley Kellow, writing in the comments said that this was wrong, and so I thought I would try to clarify things by writing to Dr Bindschadler and finding out his source. This is it.
The source is the Arctic Impact Climate Assessment apparently, although I haven't actually looked for the graph in its original location yet. You can see the 7:1 ratio in the front graph, and you will also see that the graph is comparing two anthropogenic sources of carbon dioxide, namely fossil fuels and land-use changes. Dr Bindschadler has agreed that this the graph therefore doesn't support the claim he made in the Horizon programme.
Dr Bindschadler suggests that the 7:1 figure is actually not that far out from the correct figure for net anthropogenic:natural carbon dioxide emissions, so the effect of the mistake is limited. We should note, however, that he was originally speaking about emissions rather than net emissions. But even if you look at the net figures I still don't think the numbers are correct. Prof Kellow has pointed me to this page at Skeptical Science, which puts the net figures at 29 GtCO2 emissions for anthropogenic and a net 17 GtCO2 (450-439+338-332) absorbtion from natural sources. For what Prof Nurse and Dr Bindschadler were actually talking about in the Horizon show, gross emissions, the 7:1 ratio for anthropogenic to natural becomes, by my reckoning 1:27 (i.e. with natural emissions completely dwarfing anthropogenic).*
So in terms of what is interesting us here, the figures in the Horizon show were clearly completely wrong, which I guess we knew. It's good to have confirmation of this though. The question is, what does this mean for Prof Nurse and the reputation of the BBC?
*Note that the Skeptical Science page is talking in terms of GtCO2 while Dr Bindshadler was talking Gt carbon, but it's the ratios we are interested in.