No time for carbon
Before we dive into a discussion of climate and carbon and change, we should first step back and establish a shared understanding around the timescales that are relevant to the discussion. The XKCD comic “Earth Temperature Timeline” is a good place to start, take a minute to check it out.
Now that you are back from the last 20,000 years of history we should talk about humans. Humans have been around, in a more or less modern recognizable form, for about 200,000 years. Temperature records over that kind of timescale are hard to come by, as most reporting stations were offline back then. We ‘know’ about temperature over about a million years of history from ice-records, trapped air with different chemical concentrations help us build a framework to estimate temperatures.
The last time the earth was as warm as it has been in the 2010s was 125,000 years ago, during the last peak between ice ages. That was only 2C above “normal” and we’re already at risk of blowing past that. If we clear the anomaly at 125k years ago we have to go a lot further back; we run out of records at about 800,000 years before finding a larger peak, with the older peaks tending to be at lower temperatures — the hot times have been getting hotter.
Depending on ice to provide temperature data has a built-in failure mode — Ice melts! A temperature anomaly large enough would melt all ice on the planet. It probably isn’t an accident, then, that we only have a million years of data and the anomaly has always been smaller than that of the penultimate inter-glacial period. A large enough temperature variance would obliterate all ice and erase the record (actually a full global melt is an extreme case of obliterating the record, global shifts in where the ice is could also erase the record without requiring that all ice melt — with the older ice cycling off over a period of time). So, we don’t know when it last happened, but somewhere around 1 million years ago we probably did melt enough ice on the planet to eradicate the historic ice record with a temperature anomaly greater than the penultimate interglacial peak of 125k years ago. It should be slightly alarming to consider that we’re threatening that peak’s ranking as highest average temperature in the ice record. It isn’t all doom and gloom, of course, we don’t know how much room there is between the last peak and catastrophic ice loss on the planet — but that’s the margin we’re currently betting on.
One Million years is a long time. But that’s the starting point for conversations about fossil fuels, stretching back up to 650M years for some deposits. What we do when we extract and burn fossil fuels like Coal, Natural Gas, and Oil is return millions of years of accumulation into active service. It isn’t that it is impossible to deal with the carbon liberated, it is that we are compressing millions of years of the work of the carbon cycle into a few tens of years — natural processes cannot keep up. Carbon shocks aren’t a new thing, though the scale and speed of what we’ve managed is noteworthy. Across the geologic record we see carbon shocks rise and dissipate on a 240,000 year cycle of rock weathering, with the full slow carbon cycle running 100–200 million years. There is a faster carbon cycle that moves much more carbon each year. The fast carbon cycle operates on a normal living thing lifetime cycle, around 1–100 years. With fossil fuel consumption we are shifting a resource accumulated over the slow cycle into the fast cycle. The fast cycle currently services ~500x as much carbon as the slow cycle each year, but to do it requires the entire biomass of the planet. This suggests that adjusting the capacity of the fast cycle requires changing the available biomass, unfortunately our current warming is already leading to mass extinctions and a reduction in total biomass worldwide taking us in the wrong direction for handling the extra load. There is the other complication where humans haven’t been around, as a species, for even one cycle of weathering draw-down and we’ve emitted as much carbon in the last 30 years as we have in the previous 200,000. The timescales don’t work out in our favor here.
Another thing to take into consideration has to do with the relative size of the two cycles. Even though the fast cycle moves around 500x more carbon per year than the slow cycle the cycles are so vastly different in timescale that the amount of carbon bound up in each cycle is comically different. If we call the fast cycle ‘balanced’ on 1 year and the slow cycle balanced on 100 million years we see that the slow cycle binds up around 300,000 times as much carbon as the fast cycle. This should give us pause, we would find doubling the biomass on the planet an impossible dream much less increasing it by a hundred thousand times. In contrast we can liberate large chunks of the slow cycle’s storage relatively instantly by burning fossil fuels (we couldn’t hope to liberate all of it, since we’d have to burn mountains, the crust really, to liberate it and even in our nightmares that’s not something we have in our power to do). The take-away from this digression is that one of these cycles is much easier to work with on the sinking side of the cycle, even if both are about the same on the emissions side and most of the carbon is bound up in the hard to sink cycle. When we shift the carbon load from the slow to the fast cycle we’re putting stress on the fast cycle, and due to the size of the two cycles we could (and have) casually overwhelm it — we’ll revisit this when we discuss carbon capture, though you can probably already tell that I view most carbon capture and especially sequestration strategies as unsuited to the task.
We can probably live through a new Million Year peak temperature; humans developed during a local maximum and are now into their 3rd temperature spike as basically the same species. That’s comforting from the perspective of survival of the species, but not so much in terms of the expected massive disruption and loss of life from such a swift and dramatic change around the globe. Missing our survivable climate exit by staying on the global warming highway and melting all ice on the planet, however, is a whole different kettle of fish. That takes us out of the realm of human experience and survival. We don’t know what will happen, only that it will be very bad and the right answer in terms of cosmic comedy would be for our works and bodies to become the fossil fuels of the planet Earth some 650 Million years from now.
While I do enjoy a good comedy, I’d prefer to see this play out in another way.
To sum up:
- We are on track to exit our historical known temperature record, which takes our species into the unknown, and potentially beyond the conditions favorable to our continued survival.
- Human experience spans many iterations of the fast carbon cycle, but only the tiniest fraction of a single slow carbon cycle.
- Fossil fuels represent a bulk transfer of carbon from the slow to the fast carbon cycle.
