Planetary Limits – fresh choices

Planetary Limits – fresh choices

The 1970’s classic volume Limits to Growth has influenced futurists and policy makers for a generation. Recently the assumptions in the computer model behind the conclusions, and the conclusions themselves, have attracted a flurry of interest.

We explored the Limits to Growth assumptions and conclusions for our book New Shoots, which is due to be published in October. What we concluded was that some of the assumptions and conclusions in their core scenario “Business as Usual” (see below) still hold.

For instance pollution of air, water, and land is a major concern and is estimated to kill more people each year than the Covid-19 pandemic in total so far.

Industrial output per person – definitions of productivity for the knowledge economy are difficult but conventional measures of industrial productivity have stalled.

The most notable divergence of the actual situation now from the model is that the food per person has continued to increase and has not collapsed as the model predicted. Food shortages today are local and largely due to losses in the supply chain (estimated at up to 40%) rather than due to inadequate worldwide production. The improved food supply has been achieved through a combination of public awareness, globally-based scientific advance (the Green Revolution starting in the 1970’s) and support from governments.

Limits to Growth assumptions were of their time, when people had less choice. Since 1970 more people have been able to exercise choices; their incomes have increased as they benefit from planetary economic growth. This is illustrated by the fact that predictions for the world’s population now are for it to peak in this century and then to fall slowly. The model forecast a sharp decline due to food shortages. What is actually happening is that women are choosing to have fewer children.

The most dramatic prediction of the Limits to Growth model was the catastrophic exhaustion of natural resource. Certainly, some natural resources are near exhaustion – lithium is causing concern as we write. But when we started to explore one of the natural resources often flagged as being in crisis – water – we found that the evidence was complex.

Water shortages have hit the headlines. Perhaps the most publicised was when Capetown in South Africa was facing DayZero – when it would run out of water, on April 12th, 2018. A number of factors averted this, including diverting water from agriculture, publicising water maps at household levels and “dirty shirt” challenges (who could wear a shirt without washing it the for the longest time). These measures pushed DayZero back until June, by which time the rains finally arrived.

The role of water is discussed in an excellent BBC4 series“H20:the molecule that made us”. What we know is that global average rainfall has increased slowly since 1900; that climate change is having the effect of making wet regions wetter and dry regions drier; and that weather (including rainfall) is becoming more erratic and extreme.

Since 1900, the world’s population has approximately quadrupled. Better standards of living increase a person’s “water footprint”. Can water supplies meet the demand over the next decades?

Many water supplies are from aquifers and glaciers. Worldwide, aquifers are not being replenished as fast as water is being extracted. Glaciers are shrinking due to global warming. The sources mostly used for water are under threat. Water is bulky and not usually transported long distances. So water shortage has all the makings of a “wicked” problem, one which has only bad solutions.


The precipitation falling over land each year is approximately 35,000 bn cubic metres. Usage is approximately 4,350 bn cubic metres pa, about 12% of the rainfall each year. So would this suggest one avenue for at least a partial solution to water shortages? To harness more rainwater? This has often been implemented as a household level activity and would need to be scaled up to tackle the shortfall. We see few New Shoots of planning to harness rainfall at the scale needed.

A small positive example is taken from El Hierro, an island in the Canaries. More than 20 years ago, the government planned to relocate the 11,000 inhabitants, but they decided on a different future. Their first project was to become self-sufficient in energy and water. They chose windmills and water basins with height differences as their method for energy supply. “Free” energy allowed them to desalinate additional water. And they merged the energy and water companies to prevent conflict of interest. Developments followed in agriculture, sustainable fishing, a winery cooperative and a methane biodigester which turns waste into energy and fertilizer. They offer visitors gastronomy, paragliding, hiking trails, and scuba and volcano diving.

To conclude, we were surprised when we checked the world’s water usage against planetary rainfall. It reminded us yet again to check the evidence.

Backup data and the examples are to be found in the Pearltrees associated with New Shoots – people making fresh choices in a changing world.

Written by Patricia Lustig, SAMI Principal and Gill Ringland, SAMI Emeritus Fellow 

The views expressed are those of the author(s) and not necessarily of SAMI Consulting.

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