Carbon Climate Economy Plumbing

The carbon-climate-change problem is more interesting that it might appear at first glance. I am not referring to the human, political or technological sides of the problem, complex and important as they are. Rather, I am referring to the core issue of carbon emissions and climate change itself. Most of us think we understand this part by now. We emit carbon, in the form of carbon dioxide, from cars, power plants and other sources. This goes up into the atmosphere and stays there. With more carbon dioxide in the air, the atmosphere becomes more efficient at trapping heat that would otherwise escape from the Earth's surface. Therefore, the world warms up. An analogy is that the extra carbon dioxide is similar to adding extra layers of glass onto a greenhouse, hence the term 'the greenhouse effect'.

There is a lot of truth to this way of explaining the problem, but it misses several crucial issues, most of all the complexity of the global carbon cycle. The traditional view of the carbon dioxide problem invites us to think of the system in very simple terms. A affects B affects C. In this case, 'carbon dioxide emissions increase carbon dioxide concentrations, then carbon dioxide concentrations affect temperature'. We can even skip the intermediate step and just say 'carbon dioxide emissions affect temperature'. In reality, by contrast, various complex biological processes continually circulate carbon between the atmosphere, plants, soil, the oceans, and other carbon pools. A affects B, C, and D. B feeds back on A, and affects D, and E but doesn't affect C very much. E affects A and D. And so on. Every part of the cycle, from photosynthesis, to the rotting of soil, is sensitive to carbon dioxide, climate, or both. Every part is being affected by humans directly, through processes like deforestation or agriculture. And the magnitudes involved are huge: for example, every year, just the carbon cycled through land plants is 10 times greater than the amount emitted by humans.

Now we can see that the key question is actually this – what happens to this huge, complex carbon cycle when we pump extra carbon dioxide into it? Right now, believe it or not, the carbon cycle is squirreling away half of our emissions, acting as a huge break on climate change. A natural service worth trillions of dollars and who knows how many lives. But will this service continue? Or will the system go haywire and cause global climate chaos? Over recent years scientists have learned a lot about this issue. Nonetheless, the behaviour of the carbon cycle is still one of the largest uncertainties in projections of climate change.

To understand what it means to perturb a complex system like this I want to try two analogies. First, the economy. Imagine you are the chancellor. At first glance it seems obvious that if you have your exchequer print more money, your citizens will be better off. There would be more money around, so everyone would be richer, right? Well, indeed, if you suddenly print more money, there might be some kind of temporary spike in consumption. But then, most likely, all kinds of forces will come into play to counteract this effect, which may go on to cause economic chaos. Interest rates might rise, the prices of goods, services, and houses, might soar. Borrowing might rise, not least because house prices have gone up, enabling those who own their own houses to borrow against them, causing yet another temporary spike in consumption. On the global stage, your currency might drop in value, causing a spike in exports, but making foreign goods less affordable to your citizens. And on it goes, as more and more negative processes kick in. Your economy may eventually get back to something like normal – except that your citizens feel disgruntled, unemployment has risen, and house repossessions and business bankruptcies are on the rise. And anyway, who says that spike in consumption actually made people happy even while it lasted? As the chancellor you can't believe what has happened. You had the best of intentions. Why didn't all that extra money make things better?

A second analogy is plumbing – a complex system that moves water around your house, and which has many different external controls (like stopcocks), internal controls (the ballcocks that stop your storage tanks and toilets overflowing), time-varying outputs (taps, dishwasher, washing machine) and safety outlets like overflow pipes. You figure as follows. Surely if I ramped up the water pressure, it would mean you'd get more water out of the tap when you opened it, and your toilet cistern would fill more quickly? So you try this and it works. Your storage tanks are filling faster, but the ballcocks are stopping any problems. All good. So you ramp up the pressure even more and things get even better. The ballcock in your main storage tank has failed, but you don't realize because the extra is exiting through the overflow pipe, so it doesn't cause any real problems, at least for now. So you keep ramping up the pressure, but suddenly your toilet cisterns fail, your overflow can't cope, and you flood your whole house. You're amazed. The plumbing was already circulating lots of water before, so what was the big deal about circulating more? And why didn't is show any signs of collapse, until it collapsed?

The analogies between the carbon cycle, economies, and plumbing, are real. Theoreticians would tend to approach all three using a 'stock and flow' modelling approach, which seeks to understand and simulate a system in terms of a currency (carbon, water, a real currency, or something else) that is moved between different pools. For many systems we can easily end up thinking in terms of tens or hundreds of pools connected by many more flows. In such complex systems, the dynamics can be highly non-intuitive, even if the individual parts are quite simple, or behave as if they were. We can see tipping points, where a slow change in some factor initially has a negligible effect, before causing a dramatic shift to another regime. All of which would be OK, if not for the fact that our climate and our economy are looking worryingly unstable at the moment. And as for my plumbing...

@drewpurves