Global Carbon Budget
Where does this figure come from?
The IPCC Climate Change 2014 Synthesis Report (p64) states that globally:
For a 66% chance of staying below 1.5˚C we have 400 GtCO2 left to emit from 2011
For a 66% chance of staying below 2˚C we have 1,000 GtCO2 left to emit from 2011
A Gt of CO2 is a billion tonnes (1,000,000,000 tonnes)
A 66% chance is two bullets in a six bullet gun in a game of Russian roulette. I'm not sure these are good odds of staying safe.
A 66% chance is two bullets in a six bullet gun in a game of Russian roulette. I'm not sure these are good odds of staying safe.
The global temperature has already risen by about 1˚C compared to pre-industrial levels. And there is some evidence that the amount of CO2 now in the atmosphere will lead to over 1.5˚C temperature rise over the next few centuries even if we stopped all emissions immediately. But, being hopeful and assuming we still have a chance to stay below 1.5˚C, continuing:
A 2˚C rise in temperature is considered by the IPCC to be the threshold between relatively “safe” and dangerous warming. A chance of 66% is a 2/3 chance of staying “safe”.
Many climate scientists think this is a dangerously high and unsafe target and we should aim to stay below 1.5˚C (e.g. James Hanson ).
Bill McKibben at 350.org are asking for a budget of 565 Gt CO2 from 2012. Island nations are desperate for a 1.5˚C target in order to continue to exist.
Many climate scientists think this is a dangerously high and unsafe target and we should aim to stay below 1.5˚C (e.g. James Hanson ).
Bill McKibben at 350.org are asking for a budget of 565 Gt CO2 from 2012. Island nations are desperate for a 1.5˚C target in order to continue to exist.
So we could aim to release less than 400 Gt CO2 to stay below 1.5˚C and make sure we definitely emit less than 1,000 Gt CO2 to stay below 2˚C.
But it is already the end of 2015
We have already used an estimated 158 Gt CO2 between 2011 and 2015 . See www.globalcarbonproject.org for details (fossil fuel and land use emissions 2012-2015.
So for a 66% chance of staying below 1.5˚C we have 400 - 158 = 242 Gt CO2 left to emit
For a 66% chance of staying below 2˚C we have 1,000 - 158 = 842 Gt CO2 left to emit
As the graph above shows, we are still on an ever increasing annual emissions track. More than half of which has been emitted since 1970 (chart on right). Globally we will have to drop to near zero by 2050 to reflect these budgets as shown in the IPCC graph below - dark blue line (RCP2.6 – equates to likely under 2˚C warming).
RCP2.6 Assumes that we will emit more GHGs than is compatible with a 2 degree temperature rise and then assumes that there will be some amount of carbon sequestration, ("sucking" carbon out of the atmosphere, by Carbon Capture and Storage (CCS - as yet unproven at scale) or soil / biomass sequestration).
As carbon sequestration is unproven at scale, this is a risky assumption.
As carbon sequestration is unproven at scale, this is a risky assumption.