Someone recently suggested that we needed to remove carbon from the atmosphere, which got me thinking about the optimal CO2 level, and with it, optimal levels of all sorts of things – population, cattle, sheep, rice and materials of all kinds.  None of us want to live next to a quarry or mine but we all want the products.

With atmospheric CO2, the world has varied between about 200 ppm and 5000 ppm.  200 is probably too low, creating problems with cooling, Ice Ages and plant growth.  About 900 ppm is optimal for controlled growth of plants but in reality, this is probably for weeds rather than commercial crops.  Who wants to live on Lincoln weed? It will also most likely have massive planetary warming effects.

James Hansen has suggested 350 ppm as the optimum and there is a movement for pushing for this level.  I can’t find any science to back it up, just that is what we had about 40 years ago.  In some ways I guess it is optimal, in that plants and animals were recently acclimatised to that amount.

The world is working toward net zero by 2050 which will take us to about 450 ppm or so.  Is that the optimum, or should we then look at removing CO2 from the atmosphere (net negative)?  Would plants and animals have acclimatised to the new levels by then?  Is stability more important than an actual target number?

My guess is that 450 ppm is going to be difficult to achieve and maintain with the world as it is.  So perhaps what is achievable, is also what is optimum. By the time we got back to 350 would it still be optimum?

Oil and gas production also have an optimal level for an enjoyable world.  I know that many will say that we should go to zero immediately, but this is hardly possible.  The move to EVs and green hydrogen will sort transport over the next twenty years or so, although air transport and shipping may still be problems.  Electricity generation could also be relatively fossil fuel free by then.

Feedstock for multiple modern products will still be a major issue; everything from plastics to fertiliser and pharmaceuticals. Disposable plastic is a no brainer and we need to move on from it as soon as we can.  SA has had bottle deposits for 40 years and no plastic shopping bags for 12 years and is currently moving on from plastic straws, cutlery etc. with no disruption to lifestyles.

Other plastics are a serious part of our lifestyle; our clothing, electronics, medical and surgery supplies, synthetic rubber and many other items.  Bioplastics and biofuels are an interesting option, but the amount of land needed seriously affects our ability to grow enough food.  Increased palm oil production is already a major land use problem.

My feeling is that the use of fossil gas is going to be required well into the future.  Production will need to become net zero in the way of emissions or close to.  A plastic that lasts 1000 years is probably not too much of a problem as it is essentially locking up the carbon for that time.  Clothes made of synthetics, which break down into microplastics in the wash, are a more serious issue.

If we want to go back to natural materials for clothing, we have that optimisation issue again.  How much land and resources do we need for cotton, wool, bamboo or hemp production instead?  It seems to me that we should use more natural materials and keep those clothes for a longer time.

Rice farming is as problematic as cattle breeding in a greenhouse gas sense.  Both produce copious amounts of methane.  No one is suggesting zero rice production over the next fifty years and similarly zero beef is just as unlikely.  Optimising our beef, rice, sheep, lentil etc production is the way to go but obviously a difficult result to achieve.

Our 2050 greenhouse targets should be based on achievability, science and the tools of optimisation.  Playing politics with them is not the way to go.  Whatever we do, we need to be in step with the rest of the world.  We have no car manufacturing ability of our own and rely on others completely.  Our infrastructure, tax structure and facilities need to be in lockstep with the major car manufacturers.  Our fuels should be largely domestically produced.