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

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.

* 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.