Dr Judith Curry insists, quite correctly, that we should take uncertainties into account when deciding Climate Change policy.
Yet I think our respective positions probably strongly differ on which way we weight the uncertainties.
I strongly favour the Precautionary Principle, implemented Early, making it the “Early Precautionary Principle”.
One of the reasons I come down on this end of the spectrum of possible responses to uncertainties is that there are quite a spectrum of unknowns that form the pillars of those uncertainties.
After all, if we don’t know a term in an equation, how can we possibly calculate anything meaningful with any kind of confidence ?
How can anybody feel safe and secure not knowing for certain what the actual equilibrium Climate Sensitivity amounts to ? The response of the Earth’s Climate system to extra airborne Carbon Dioxide-forced temperature rise is a number that is becoming firmer, but there are error bars. Surely this points to conservatism in emissions ?
Moreover, we could be well advised to cut back on Fossil Fuel burning not just to protect the Climate, but to save the Economy. How can we pursue our normal everyday Carbon-emitting lives not knowing how much Fossil Fuel there is left in the ground that can be inexpensively mined ?
How can we know the order of magnitude of Fossil Fuels left to extract ? And how can we know what kind of impact this will have on the Climate ?
Let’s start with how we got here in the first place, with stores of Fossil Fuels in the Earth’s crust. Dismissing ideas based on the Young Earth Theory, and the invention that there may be non-biological sources of petroleum and Natural Gas, we arrive at the geological timeline, that connects atmospheric Carbon Dioxide levels with biota productivity and mass extinction events. When Carbon Dioxide levels have been much higher than today’s in the deep geological past, lots more micro- and macro- plants grew, and then died, and sedimentised, locking down that Carbon out of the air :-
It roughly translates, in my mind (somebody please correct me), as two distinct phases of Earth history where Carbon Dioxide got sucked out of the air and laid down into the crust.
In the period leading up to the end of the Carboniferous period, the amount of Carbon Dioxide sucked out of the air and laid down was very, very approximately taking the atmosphere from 7000 parts per million (ppm) Carbon Dioxide (CO2) down to 350 ppm CO2, that’s roughly 95% of 35,000 petagrams CO2, which is 33,250 petagrams (Pg) or billion tonnes or gigatonnes (Gt) of CO2.
Thereafter there was some volcanic activity that put more Carbon Dioxide in the air, and in the period up to the end of the Cretaceous, another bunch of CO2 was locked down, very very approximately taking the atmosphere from 2000 ppm CO2 down to 350 ppm CO2, 85% of 10,000 Pg CO2, which is 8,500 Pg, Gt CO2.
Add these two amounts together and divide by 3.44, you get a lock down of roughly 12,000 gigatonnes of Carbon, which is roughly what’s in the black box marked as “COAL OIL GAS” in this diagram, so probably the right order of magnitude (without looking at the ocean sediments). This was basically cut from the Global Carbon Cycle, never to be circulated to air again…until we started digging it up :-
There are various views on how much of this has really been laid down as usable hydrocarbons, and how much of it has been degraded, and whether much of it is accessible.
I’m going to summarise a mish-mash of values, taken from the Intergovernmental Panel on Climate Change (IPCC), (largely based on oil and gas company data), and also from Professor David Rutledge at CalTech :-
A calculation on the IPCC estimates of conventional Fossil Fuels left to burn would put very roughly 1,000 gigatonnes of Carbon (Gt C) back into the atmosphere (as 3,440 gigatonnes of Carbon Dioxide (Gt CO2)).
Compare this to the calculations of George Monbiot, where he calculates 818 Gt C (2,814 Gt CO2) :-
A calculation on the IPCC estimates of all possible types of Fossil Fuels (including Methane Hydrates) would put roughly 4,000 Gt C back into the atmosphere (as 13,760 Gt CO2).
From projections of conventional Fossil Fuel production, Professor David Rutledge puts Coal left to burn at 847 Gt, and Petroleum Oil and Natural Gas left to burn at 618 Gtoe (gigatonnes of oiil equivalent), making approximately 500 Gt C to go back into the atmosphere if this were all burned (1,720 Gt CO2).
So Professor Rutledge can only see one part in twenty-four of the locked down Carbon being re-released, but the IPCC can see somewhere between one part in twelve and one part in four (roughly speaking).
David Rutledge uses Climate Change modelling software to claim that his projections of temperature rise from Global Warming will not cross the 2 degrees of warming considered the “safe” threshold by the United Nations Framework Convention on Climate Change.
However, David Rutledge does not consider unconventional Fossil Fuels, so he may need to revise his projections in further work.
Besides which, there are various voices, based on research, that suggest that the “safe” threshold for Climate would only permit far lower levels of emissions than the IPCC lowest figure, and even lower than Rutledge’s figure :-
“Abstract…Limiting cumulative CO2 emissions over 2000–50 to 1,000 Gt CO2 [290 Gt C] yields a 25% probability of warming exceeding 2 6C—and a limit of 1,440 Gt CO2 [419 GtC] yields a 50% probability—given a representative estimate of the distribution of climate system properties…”
There’s nothing really special about the 2 degrees Celsius “guard rail”. Climate Change is already serious, even at 0.6 to 0.8 degrees C, and there’s another roughly 1.0 degrees C locked in, yet to come, from emissions already made. Maybe we should stop adding Carbon Dioxide to the atmosphere right away to keep the place liveable…
With all these types and levels of uncertainty, surely the best response is to stop burning Fossil Fuels ?
Some may say, and that probably includes Dr Judith Curry, that this response is a response too far, but I think it’s fairly reasonable in terms of the level of caution suggested by the uncertainties :-