Full global decarbonisation of energy before 2034*

This brief blog provides the headline numbers underpinning my disagreement with Glen Peters’ (Aug 27th 2014) estimate of the time available to remain within a 2°C carbon budget of 1000GtCO2 (for the period 2011-2100).

Glen tweets that:
 “At current emissions rates it will take 30 yrs to emit enough CO2 to pass 2°C”
      In a later tweet he notes …
“The 30 years is 66% chance. About 1000GtCO2 from 2011, from IPCC WG1 SPM …

In contrast, I suggest:
- At current (2014) emission levels, the 1000Gt will be consumed in less than 23 years.
- But with CO2 certain to rise over the coming few years, then, at the likely 2020 emission level, there will be ~13.5 years until the full 2°C carbon budget will have been consumed; i.e. full decarbonisation of energy before 2034.
- This is a much more challenging decarbonisation agenda than Glen’s 30yr figure suggests
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Background to the 23-year figure (from the end of 2014)
- CO2 emissions in 2000 were 24.787Gt, in 2012 these had risen to 35.425Gt1
- This is a mean growth rate of a little over 3% p.a. for 2000 to 2012; a period that included, arguably, the most severe global financial crisis since the Great Depression.
- Assuming emissions have continued to grow at ~3% p.a., then emissions for this year (2014) are likely to be ~37.5Gt.
- The IPCC’s 1000GtCO2 carbon budget is for the period 2011 to 2100.
- Emissions from 2011 to the end of 2014 (i.e. four months from now), will be ~144Gt, leaving ~856Gt for the period 2015 to 2100.

If emissions were to stabilise at the current (2014) level of ~37.5GtCO2, the remaining 865Gt would be used up in 23 years; i.e. during 2037. 

Background to the under 14-year figure (from the end of 2020)
- Given the Paris 2015 COP is, at best, seeking agreement on post 2020 mitigation, emissions are almost certain to grow over the coming few years.2
- Assuming current emissions continue grow at ~3% p.a., then emissions for the year 2020 will be ~44.8GtCO2.
- Following on from the above, by the end of 2020 in the region of 394Gt of the 1000Gt will have been emitted, leaving a budget of  ~606GtCO2 for the period 2021 to 2100.

If emissions were to stabilise at the ‘likely’ 2020 emission level of ~45Gt, the remaining 606Gt would be used up in under 14 years, i.e. before 2034.
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* NB: if Annex 1 nations were to begin a programme of radically reducing their energy consumption (& hence emissions) over the coming decade, there may be scope for non-Annex 1 nations to continue emitting energy-related CO2 out towards 2050

1 Figures taken from the Global Carbon Atlas http://www.globalcarbonatlas.org/?q=emissions
2 It may well be that emissions growth actually exceeds the 2000-2012 mean level (~3% p.a.),
particularly if the global economic ‘recovery’ continues.

To get an early response to Glen’s estimate, I have pulled the above analysis together in quick fashion; if there are any important errors (in the numbers or maths) please feel free to email me – thanks.