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Carbon confusion - Josh 292

I had a request from Richard Betts to do a cartoon on this paper in Nature about soil CO2 emissions. The abstract says soil emits "60 petagrams of carbon per year to the atmosphere as carbon dioxide”.

It made me wonder why they talked about 'carbon' and not 'carbon dioxide' - after all, carbon is not a greenhouse gas. And why use petagrams and not gigatons, or is it gigatonnes? 

I found out that a petagram is the same as a gigatonne or metric gigaton, but not a UK or US gigaton. Also the reason scientists use 'carbon' and not 'carbon dioxide' is that they are referring to the carbon cycle (carbon as fossil fuel burns to create CO2 which is reabsorbed by plants and converted back to carbon).

But between the scientists, the politicians and the media it is easy to get a bit confused. For example at Information is Beautiful you get this lovely infographic where they talk about 39 gigatons(!) of CO2 but call it ‘our carbon budget’. Their actual number for a 'carbon budget’ should be 10.6 gigatonnes not 39 (though they do note the confusion in a footnote). Richard Betts says the amount of carbon in manmade CO2 emissions from fossil fuels are, in fact, 8 gigatonnes per year.

When you look at the data behind the infographic they add to the confusion by talking about 'carbon emissions’.

Back to the Nature paper, we learn that "the response of soil microbial communities to changing temperatures has the potential to either decrease or increase warming-induced carbon losses substantially.”

Add this to the 60 petagrams of soil emissions, which dwarfs the manmade emissions of 8 Petagrams, and you have a lot more uncertainty - of the natural kind. 

Many thanks to Richard Betts and Nic Lewis for helping with the research, educating me and correcting mistakes.

Cartoons by Josh

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Reader Comments (5)

I trust you used a long spoon when collaborating with the Ungodly, Josh.

Sep 8, 2014 at 9:22 AM | Unregistered CommenterKevin Lohse

The more realistic comparison for 'petagram' is as a milder form of 'stripagram'. Teasing, arousing passions, but then reality kicks in with the realisation it's merely attention-seeking.

Sep 8, 2014 at 10:27 AM | Unregistered CommenterJoe Public

"Richard Betts says the amount of carbon in manmade CO2 emissions from fossil fuels are, in fact, 8 gigatonnes per year."

For comparison, perhaps someone could advise of the amount of carbon in real man-made CO2 emissions, from the global population exhaling?

Sep 8, 2014 at 10:32 AM | Unregistered CommenterJoe Public

The more likely explanation for the use of peta-grams is it sounds like a much bigger number as it is 10 to the power 12, whereas giga is a mere 10 to the power 9! The difference between tons (Imperial) & tonnes metric, is minimal in terms of a few kg! Sounds very much to me that's is what they're playing at, petty really.

The estimated emissions by Human activity is c35Gt CO2, estimated net total emissions Natural & Human, c750Gt, (UNIPCC AR4:2007). I expect they've tweeked it since then.

Sep 8, 2014 at 5:52 PM | Unregistered CommenterAlan the Brit

Surely uncertainty of that magnitude puts the cat firmly among the pigeons - and all pets are off!

Sep 8, 2014 at 10:42 PM | Unregistered CommenterJ Calvert N

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