Thinking about models…

This week I have been thinking about models, and not the glamorous type, in fact rather the opposite. The types which seem to mainly predict catastrophe and environmental collapse.


I’ve been focusing a lot on The Limits of Growth, the 1980s book, discussing a dynamic systems model of the world. It uses an essentially simple premise – that of feedback loops, for example in population. Population, in simple terms is a product of the interaction of two feedback loops, one positive (birth rate) the other negative (death rate). In the world as a whole, the birth rate is greater than the death rate so the population grows. The added complication is that in the following year that birth rate is then applied to a new (increased) population. So instead of growing at a steady rate, the population is continually increasing by a multiple, and therefore growing exponentially.

Obviously in an attempt to model the world, there are lots of other feedback loops involved, eg per capita income, pollution etc. More complicated still, these feedback loops feed into each other, for example a decrease in food supplies in turn feeding into a higher death rate. Complex though this may be you can see how it may be feasible to build such a systems model, run them through a computer, and see what happens… the results – pretty much universally bad news on most runs of the model. With resources diminishing, population and pollution increasing until reaching a critical point where normally either food supplies or pollution inflict a massive population crash. More powerfully still they show how changing basic assumptions, for example assuming we have twice as much natural resources as we thought, or from the 80s onwards begin to recycle everything, really doesn’t change the picture too much – the critical and fairly intuitive balance is that between exponential growth of population set against limited resources.

This is an old model, fairly basic in its assumptions, and that is enough for many people to dismiss the findings. But later in the week I heard a fascinating presentation from DECC during which I was introduced to my new favourite internet toy. DECC have developed a great online model where you can play with making different changes and see the effect it has towards meeting UK carbon emission targets. For example picking energy mix, moving to solar, or wind, insulating houses, increasing recycling etc. It is fascinating to play with the dials and see the effect it has but one of the clear messages was we need major changes to meet the UK’s target of an 80% reduction in carbon emissions by 2050. The list of different measures each has a level where you can chose, for example between 1 (do nothing) to 4 (do everything you feasibly can). It is probably no surprise that it requires lots of number 4s in lots of areas if we are to reach the 2050 target!

Another model described in another lecture looked at EU emissions targets for things like Nitrogen and Sulphur oxides. Here there was some better news, seeing real progress on many fronts, introduction of new technologies, showing cost benefits, which have convinced both governments and business to make real strides against these targets – many of which have been over achieved. Even here there was a familiar message, there is still a lot to do.

For me these models are powerful, as long as they are taken in the spirit they are meant, as tools, as scenario builders. The assumptions on which they are built can be easily challenged, the unknowns picked up upon and the simplicity of any model in the face of the real world raised. This is a loop we seem to be trapped in with many of the longer term, large scale issues such climate change as we argue about the detail rather than focusing on the simple, big picture the model is demonstrating.

Limits to growth starts with a powerful analogue – if you throw a ball in the air a simple model can tell you that it will go up, gradually slowing until it comes to a stop, it will then begin to fall getting fast and faster until hitting the floor.  To know exactly where it will land and how high it will rise would require a more complex model, with extremely accurate inputs and data… but we know the general shape.

All these models seem to point to a general shape which is hard to ignore and also seems to appeal to the common sense approach – we can’t keep growing, and using more and impacting more whilst reliant on finite resources. If we want to stop the ball hitting the floor we need to do something now to try to catch it.


About domhall

I have spent the last 15 years juggling careers in education publishing, expedition leadership and safety training. It has involved a careful balancing act of dreams of expedition travel, a love of climbing, walking and the outdoors and the the realities of life - and the later has definitely come off worse. I've run an adventure travel and expedition training business and lived in the sometimes sunny Lake District. Having taken a year out to complete an MSc in Environmental Technology I am now working for The Conservation Volunteers, working on engaging communities in their local green spaces.
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