Global Carbon Budgets and Wildfires | Brussels Blog

Global Carbon Budgets and Wildfires

posted by on 19th Oct 2017


Global Carbon Budgets and Wildfires
(with added RCP 2.6)

I’ve tried to keep this post understandable.
For those that don’t like too many numbers, sorry.
Sometimes the small print is important.

Carbon Budgets for 2015 and 2016

I’ve been comparing the Global Carbon Project‘s Carbon Budgets for 2016 and 2015 and found two useful diagrams. Here are the diagrams, with a little bit of extra annotation to avoid the confusion that I had to start with.

Figure 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”.

Figure A:The remaining carbon quota for 66% chance <2°C : From the end of 2014

Figure B: 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”.

Figure B:The remaining carbon quota for 66% chance <2°C : From the end of 2016

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 budget to emissions of 770 Gt of CO2.

3) Emissions of CO2 from fossil fuels have reduced the remaining carbon budget by the difference between 1542 Gt CO2 (A) and 1465 Gt CO2 (B) i.e. 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) i.e. 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.

My previous post discussed representative carbon pathways:

Representative concentration pathways (RCPs) are hypothetical emissions of greenhouse gasses and other climate pollutants. (So why are they called concentration pathways?) The RCPs specify individual climate pollutants, such as CO2, CH4, N2O and black carbon for each year from 2000 until 2100.

Four RCP’s have been chosen as standard: RCP2.6, RCP4.5, RCP 6 and RCP8.5. RCP2.6 gives the lowest concentrations of climate pollutants. According to climate models, RCP2.6 is the only RCP that keeps the rise in global average temperature since pre-industrial to below 2°C. The others have worse outcomes.

RCP’s are useful for climate scientists to test their models. They are also used in policy discussions. Policy makers point to RCP 2.6 with the message “if we can keep emissions close to RCP2.6 levels, dangerous climate change can be avoided”. (See the end of Lord Stern’s lecture, The Stern Review +10: new opportunities for growth and development.)

In Figure A, the remaining budget is split between d future fossil fuel and cement emissions and future land use change. 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”, which total 122 Gt CO2 between the end of 2016 and 2072. Year 2072 is the date that RCP2.6 goes into negative emissions for fossil fuel and cement. That’s close enough to 138 Gt CO2 to use.

Taking 122 Gt CO2 off the “total remaining CO2 quota” at the end of 2016 gives 694 Gt CO2.

Note: UK emissions

694 Gt CO2 is just over 91 tonnes CO2 each when 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.

According to my spreadsheet of RCP 2.6 numbers, the 816 Gt CO2 remaining budget (for a 2°C rise in global temperature) runs out in in 2047 – but that’s in world RCP 2.6. In the real world emissions seem to be soaring way above RCP 2.6.

Wildfires and carbon budgets and RCP 2.6

In ‘It’s alarming’: Wildfire emissions grow to triple B.C.’s annual carbon footprint CBC News reported

The largest B.C. wildfire season on record has emitted an estimated 190 million tonnes of greenhouse gases into the atmosphere — a total that nearly triples B.C.’s annual carbon footprint.


Although the provincial government records and reports the total annual emissions from wildfires, those figures are considered to be natural disturbances and are therefore not included in B.C.’s annual inventory.

This should not mean that these B.C. wildfire emissions will be hidden from the next Global Carbon Project’s budget. The GCP does count the emissions from wildfires as this image from their 2016 budget shows:

My reading

1) Forest clearances are roughly 5.5 Gt CO2/year before 1995 and a lower rate of 4 Gt CO2/year after 1995.

2) Large wildfires, (e.g. in Indonesia) emitted an extra 3 Gt CO2 in 1997 and 1 Gt CO2 in 2015.

3) The levels of “Other CO2” emissions reported more-or-less match the emissions in RCP 2.6 – except for the jumps in wildfire emissions in 1997 and 2015.

1. The 3 Gt CO2 jump in 1997 cannot be in RCP 2.6 as it  shows a fall from 1996.

2. The 1 Gt CO2 jump in 2015 couldn’t be in as RCP 2.6 was developed in 2011.

In RCP2.6: exploring the possibility to keep global mean temperature increase below 2°C by van Vuuren et. al, the developers of RCP 2.6 make no mention of wildfire activity. Also an increase in wildfire activity was not included in the computer models for the IPCC’s AR5.

Together these suggest that increasing wildfires have not been accounted for in “save the climate” scenario RCP 2.6 or the climate models which use it. Obvious questions are

1. Have wildfires been included in any scenarios for the future of our climate?

2. Why can’t representative carbon pathways be fed into climate models to tell us about the effects burning down forests, flying and eating beef?

3. How hard is (2)?

Postscript and acknowledgements

I’d like to thank Neven and his Arctic Sea Ice Forum for the opportunity to post parts of this and get helpful comments from users Daniel B. and rboyd. rboyd has commented

The research is tending to an ECS at the higher end of the range than assumed in these carbon budgets, plus they do not take into account feedbacks (soil carbon, clouds, albedo etc.), plus they underestimate the effect of methane, plus the land use numbers are highly suspect. Apart from that, these carbon budgets are really useful /sarc.

There is no carbon budget if we take any realistic view of things and/or use a better (i.e. much higher than 2 out of 3, even in Russian Roulette its 1 out of 6) probability of success.

It will be interesting to watch the UN IPCC attempt to keep the carbon budget story going when confronted with updated scientific findings.


If “natural emissions” turn out to be higher than projected, say via accelerated wildfire or permafrost decay, then to match any RCP projection human emission must be smaller. Since every indication is that the antecedent is true, i am afraid that your estimate of 90 tons/human future allowable emission is too large to meet RCP2.6

But then, I am one of those people who think that we have really zero tons allowable per capita, and we better get really busy on sequestration soon, preferably through ag practice change and reforestry.. Else WAIS will disappear and SLR will got to 10mm/yr or more for many decades, and many other bad things will happen.


sidd ( October 21, 2017 at 7:32 am )


Thanks. I agree.

I’m preparing for a discussion with the UK Committee on Climate Change. I am trying to use “official” figures.


Geoff Beacon ( October 21, 2017 at 11:31 am )

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