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The ‘trillionth tonne’ of carbon (and why we can’t release it…)

From the IFRF Office
Contributed by Philip Sharman
Sheffield, Thursday 23rd November 2017

Following our item on the UN Climate Change Conference 2017 (‘COP23’) in the last MNM and particularly the comment that “it is the cumulative inventory of greenhouse gases in our atmosphere that is the crucial factor”  where climate change is concerned, we thought you might be interested in this.

That item reported that emissions of carbon dioxide – the most significant of the greenhouse gases – are now 145% of pre-industrialised (i.e. before 1750) levels.  However, it is the cumulative emissions since that time from fossil fuel use, cement production, land-use change, etc. that is critical, and this amounts to just over 0.6 trillion tonnes of carbon.  This cumulative emission is estimated to have caused just over 1°C of global warming.  The consensus view amongst the scientific community is that a further 0.4 trillion tonnes of carbon will lock us in to a most likely warming of around 2°C, widely regarded as the threshold for serious climate change impacts.  Therefore, the concept of the ‘trillionth tonne’ of carbon, and its fate, epitomises the climate challenge we face:  If it is released to atmosphere – which current rates of emission indicate will happen in less than 40 years – we are firmly on the path to 2°C of warming.  Therefore, we must ensure that the ‘trillionth tonne’ is not released.

This topic is explored in an informative website www.trillionthtonne.org, which has an eye-catching running counter (indicating 616,596,948,895 tonnes of carbon and counting).  Two other sobering ‘counts’ also catch your eye:  Based on emission trends over the past 20 years, the trillionth tonne of carbon will be emitted in the early afternoon of Sunday 9th November (!), and to avoid its release, emissions would need to start falling at a rate of over 2.85% per year (note the comment in the ‘COP23’ piece reporting that the rate of emission is currently rising again having plateaued in the last three years).  Sobering indeed…


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