At a glance – What is causing the increase in atmospheric CO2?

Posted on 19 December 2023 by John Mason, BaerbelW

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added “At a glance” section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a “bump” for our ask. This week features “What is causing the increase in atmospheric CO2?“. More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

At a glance

Do you believe in the Tooth Fairy? A mysterious entity that turns up when people are sleeping, to remove unwanted things and replace them with something nicer? Because, you see, Murry Salby’s ramblings require a Tooth Fairy to help him out. Let’s take a look.

Murry Salby was a briefly popular character in the circus that is organised climate science denial, with the same few dozen names cropping up repeatedly in books, conferences, speaking tours and so on. If Salby was right, the army of scientists that have worked on the carbon cycle over many decades must have missed something glaringly obvious. They have not.

The fast part of the carbon cycle is represented by the annual near-symmetrical ‘wiggle’ on graphs of CO₂ concentration. The peaks and troughs of the wiggle pretty much cancel one another out. This is unsurprising when one considers their source – the living world and particularly plants.

Plants take in CO₂ when they are in the growing season – so the concentration falls by a few parts per million (ppm), hence the troughs. In the depths of winter, many plants die or enter dormancy and the opposite happens, hence the peaks. The sizes of the peaks and troughs both fluctuate together depending on things like certain natural climate cycles. For example, in the well-known El Nino Southern Oscillation, vegetation takes up more CO₂ during La Nina.

There’s also the slow carbon cycle that operates over geological time-spans of thousands to millions of years. We have a range of tools with which to interrogate the record of the slow carbon cycle. An obvious one is air bubbles trapped in ancient glacial ice and sampled from ice-cores. Over pre-industrial Holocene times (11,700 years ago-recent), CO₂ concentrations show little variation – an erratic 20 ppm (or about 7%) increase over all that time. That suggests the net natural CO₂ flux was small: what the planet was putting into the atmosphere was largely taken back out. Going back further, into the glacial-interglacial cycles, we see that CO₂ fell to less than 200 ppm in the ice-ages and in the milder interglacials it rose to about 280 ppm. That was the case from at least a million years ago.

Now, all of a sudden, CO₂ has shot up to around 420 ppm since the late 19th Century. It’s gone up 50% in less than 150 years. What’s the big difference about the world now and the one over the previous million years? The answer is the intensification of the industrial era, post-1950. Back then we were emitting 6 billion tonnes of CO₂ per annum. That figure has now risen to 44.25 billion tonnes a year – it’s gone up more than sevenfold.

If you still insist the recent CO₂ increase is not due to human activity, you need to make that 44.25 billion tons of emissions per annum (and rising) magically disappear somehow. That’s where the Tooth Fairy has to come to your aid – and as any rational person knows, it doesn’t in fact exist.

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