Image Credit: CC-BY 4.0 Shannon Fiume, 2018 https://bit.ly/2V3qP80
How much Carbon do we need to pull out of the air (and oceans) to get to a Carbon Dioxide concentration of 281 ppm, as it was in the pre-Anthropocene?
As of late last year by the latest emissions figures reported by the
Global Carbon Budget Project, we need to pull about 460 gigatonnes of Carbon or remove 1.6 trillion tonnes of Carbon Dioxide from the atmosphere.
And what’s the fastest rate could we pull this out of the atmosphere?
This question isn’t simple, as we don’t know what’s the optimal rate to pull Carbon out of the atmosphere. Here are some hypotheticals. If
were to remove all Carbon from human emissions, in the next
twenty-five years, we’d need a fast rate of removal, say slightly over 18 gigatonnes of Carbon (or about 67 gigatonnes of CO₂) per year. If we expect to reach restoration in a somewhat longer time, say 30 to 40 years, then that number could lower.
If we want to finish by 2100, when many of us have died, then we can reduce that number even further. If we lose the carbon sequestration capacity of the land sink, meaning the Carbon trapped underground or in plants goes into the atmosphere and subsequently pushed into the ocean, then the total goes up. We actually should
plan on the amount being high initially such to steer us clear of tipping points.
Why are tipping points bad?
There are large deposits of Carbon locked up in frozen methane, ice, and permafrost. Should these large quantities of Carbon get released quickly in a matter of years, or less, it will radically increase global warming. There are other tipping points, such as removing large amounts of ice cover, which would also quickly increase global warming. This radical increase in warming presents a much more difficult path where Carbon Dioxide Removal (CDR) is theoretically not able to keep pace with warming. For CDR to be successful, we need to get to emission neutral and practice removal to stop the planet from warming enough to set off
the tipping points.
Why is the amount of Carbon so much larger than the figure quoted by the
United Nations Intergovernmental Panel on Climate Change and popular press?
The way to lower Earth's temperature is estimated by the UN IPCC in climate models that break down
many hypotheticals ways into
scenarios, and some of them target to not exceed 1.5º C. Their reports use a measure of heat named Radiative Forcing, which is Watts per area of gas or body such as Earth. The lowest amount of allowable warming to not exceed 1.5º C is RF 1.9 W/m². (Outlined in the technical science reports global modeling teams use different software to model how to achieve RF 1.9 W/m². The data from these team's scenarios are used to generate the probability of attaining below 1.5º C.) Reaching 281 ppm would be a Radiative Forcing of 0 W/m² and 0º C of allowed warming.
Reaching a Radiative Forcing of 1.9 W/m² would be akin to reaching the climate of 1984, whereas a Radiative Forcing of 0 would be a climate just after the mini-ice age/global cooling in the 1790s.¹ (Search for 1984 in the previously linked NOAA reference page.) (This section is incorrect, and is corrected in this blog post:
Seeking Cooler than 1.5ºC.)
How do we get to the climate of the 1790s and why 281 ppm?
We need everyone to do everything in Project Drawdown to get us nearly emission neutral and get involved in CDR and carbon tech. 281 ppm was the global average Carbon Dioxide concentration from 600 BCE to 1750. We need scientists to identify if 281 ppm is the optimum Carbon Dioxide concentration. We don't know what the optimum Carbon Dioxide concentration is.
Scatter plot of Antarctic Ice Core CO₂ concentration data from multiple ice cores: Law Dome, Dome C, Maud, Taylor Dome, WAIS Divide, Vostok, and the
South Pole from the time of 200,000 BCE to 2004 CE. The pale green line is the mean of 280.9 from 600 BCE to 1750 CE.
By when do we need to hit Carbon neutral or emission neutral?
We need to hit emission neutral ASAP, not by 2030, or later, but as fast as humanly possible. We need to start carbon removal as soon as humanly possible to steer Earth’s climate clear of tipping points. We ought to hit double-digit gigatonnes of Carbon removed in the next couple of years. We have to scale an industry that doesn’t exist.
Go back to the safety of this much removal, how safe is it?
At this point, we don’t know. We need scientific labs to find the upper limit of how fast we can remove Carbon and not cause the climate to fall into a mini ice-age. We need labs to identify what’s the slowest we can remove and not set off the tipping points, and not have the climate extremes like the present time. While labs are working to find the fastest and safest rate, since it takes time to scale the technologies to remove gigatonnes; we need entrepreneurs, scientists, and engineers to create, enhance, and scale CDR technologies.
What can we do, how can we take climate action?
We need everyone to create, extend, and scale renewables and CDR technologies. We’ll need many early adopters to buy or try open CDR solutions. We'll need everyone to switch to the renewable option asap. These efforts will get the economic engine to prefer recycled-emissions carbon-based goods. And we need everyone to get involved in CDR now, and so we can go carbon negative!
¹ In the paper Alternative Method to Determine a Carbon Dioxide Removal Target, as well as in "A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation", the historical RF precedent is used to substantiate temperature in the place of generating a model.
