CARBON BUDGETS AND RCP2.6
I've been looking at this further and been comparing the Global Carbon Project's Carbon Budgets for 2016 and 2015 and found another useful diagram. I had some confusion due to the fact that the diagram in the “2015 budget document” showed data to the end of 2014 but the similar diagram in the 2016 budget document showed data to the end of 2016 - moving on a year. Here are the diagrams, with a little bit of extra annotation.
A: From
Carbon Budget 2015: Heading “The total remaining emissions from 2014 to keep global average temperature below 2°C (900 GtCO2 ) will be used in around 20 years at current emission rates”.
From
Carbon Budget 2016: Heading “The total remaining emissions from 2017 to keep global average temperature below 2°C (800 GtCO2 ) will be used in around 20 years at current emission rates”.
I interpret the diagrams like this
1) “Total quota 3670”: 3670 Gt CO2 is 1000 GtC as per Allen et. al
Warming caused by cumulative carbon emissions towards the trillionth tonne.
2) “Non-CO2 770”: It is assumed that the effect of non-CO2 pollutants will have a similar climate effect on the carbon buget to emissions of 770 Gt of CO2.
3) Emissions of CO2 from fossil fuels between the ends of 2014 and 2016 have reduced the remaining carbon budget by the difference between 1542 Gt CO2 (A) and 1465 Gt CO2 (B) ie. 77 Gt CO2. This is two years worth of fossil fuel and cement emissions (38.5 Gt CO2/year?).
4) Emissions of CO2 from land use change have reduced the remaining carbon budget by the difference between 542 Gt CO2 (A) and 533 Gt CO2 (B) ie. 9 Gt CO2. This is two years worth of fossil fuel and cement emissions (4.5 Gt CO2/year?).
5) The “total remaining CO2 quota” has reduced from 903 Gt CO2 to 816 GtCO2 i.e. by 87 GtCO2. That averages at 43.5 Gt CO2/year.
In (A) the remaining budget is split between future land use change and future fossil fuel and cement emissions. I'm not sure where the “Future LUC 138” comes from but I note that the numbers given in the RCP2.6 tables give “Other CO2 emissions”. These total 122 Gt CO2 between the end of 2016 and 2072. Year 2072 is the date that RCP2.6 goes into negative emissions fossil fuel and cement.
Taking 122 Gt CO2 off the “total remaining CO2 quota” at the end of 2016 gives 694 Gt CO2.
That's just over 91 tonnes CO2 each when it's spread over the world's population. Using this methodology, I think we may have about 25% extra budget to emit non-CO2 emissions. That would take us to 120 tonnes CO2e each.
The average UK citizen gets through that in about eight years – if we do the decent thing and measure emissions on a consumption basis rather than cheating and measuring on a production basis like our government does.
However, there's lots of reasons for thinking the climate situation is worse.
Anyway, according to my spreadsheet, RCP 2.6 runs out of the 816 Gt CO2 remaining budget in 2047 and that budget is for a 2°C rise in global temperature and we seem to be soaring way above RCP 2.6.
