Net Zero Carbon

Net Zero Negative Carbon 

How Big Are The Holes In The Net?

Most people think that Net Zero Carbon means no more fossil fuels, but that is not true. 

Anyway we need Net Negative Carbon in order to get carbon dioxide (CO₂) levels fixed.

I'm a sceptical and curious person so I check things out. The internet is full of data and I encourage anyone who can put numbers in a spreadsheet to check my findings. Findings have to be reproducible, according to the scientific method.

Can you spot the loophole?

In order to keep CO₂ levels low enough to keep us below a rise of +2°C or even +1.5°C, as agreed by the Paris Agreement, we have to reduce our emissions, but by how much?

This diagram - Figure 6.1 Simplified schematic of the global carbon cycle - is from IPCC AR5 Climate Change 2013: The Physical Science Basis - Chapter 6 - Carbon and Other Biogeochemical Cycles. 

The global ecosystem, Gaia, is generous. If you add up the numbers for CO₂, about half of atmospheric increase is sequestered naturally by the land and sea. So if we reduce our emissions enough, can we get away with not reducing them to zero? As emissions fall below what is naturally sequestered, CO₂ levels start to fall, and of course so do temperatures. Put another way - When this diagram was created for AR5 we emitted about 9 GtC/yr but only 4 GtC/yr stayed in the atmosphere. So about 5 GtC/yr was naturally sequestered.

I put some figures into a spreadsheet to create a very rough model, and this below is what I found. Even reducing carbon by as little as 75% makes temperatures peak below +2 °C and then start reducing. Note that temperatures peak at the point where Net Negative Carbon begins.

It's no surprise that if we don't reduce emissions enough, then temperatures carry on rising.

The quicker and deeper we make the cuts, the quicker temperatures get back to near normal.

Even only cutting 75%, if done quickly enough, keeps us below +1.5 °C.

The IPCC AR6 talks about an annual 5% cut, which results in this graph heading for zero emissions. Personally I think that my pattern is better - based on a tanh curve. Start to make the changes slowly and as the momentum builds, speed up as momentum gets under way, and slow down as the really difficult changes have to be made. Also heading for sustainable levels is more realistic.

Obviously this is just a very simple model that does not include methane or feedbacks, but as they say, "All models are wrong, but some are useful". That's because a model is always an approximation to the reality it's trying to model. This isn't supposed to be the final answer, but I hope this gives some hope, that if we haven't already passed too many tipping points, there is a reasonable way out of the global overheating and climate chaos crisis.

As a check on my model I improved it to be a bit more subtle. We know that currently about half of emissions are naturally sequestered so I investigated historic records of emissions and atmospheric concentrations and found this.

My assumption is that there is a relationship between the amount of CO₂ naturally sequestered and the excess above the preindustrial norm of 280 ppm. This seems to be true and leveling off at about 2%.

This graph above is based on the same parameters as the first graph on this page, but with the 2% assumption, and gives even better results.

But I've a feeling that we should be aiming to reduce carbon to world war 2 levels. Something happened immediately after WW2 that changed the ratio shown by the green line on the graph below.

So that would mean reducing carbon according to the graph below.

There is one major limit to my simple model, it assumes a linear relationship, but the Earth's atmosphere and ecology is a complex system that if pushed beyond tipping points is likely to flip into a very different state. Which is even more reason to act quickly.

Further investigation into measured historic CO₂ atmospheric levels and estimated emissions shows that neither the 50% of emissions nor the 2% above 280 ppm rules fits the historic data. Counterintuitively it would appear that historically the higher the CO₂ concentration, the less of it is naturally sequestered.