Revised 2 December 2023


John Holdren and Paul Ehrlich (1971) provided a broad-brush measure of the impact of human activity on the environment in the form of an equation where the impact equals the level of the population multiplied by the level of affluence multiplied by the level of technology. 




Figure 1: Impact of Humans on the Environment (Holdren & Ehrlich 1971) 


As mentioned already, the current world population in 2021 is 7.9 billion. Population growth still remains the elephant in the room. It is a taboo subject and it is politically incorrect to suggest that any country should limit the size of its population. For some people, the right to have as many children as you want is sacrosanct. 


Even if all countries were to adopt a Zero Population Growth policy overnight – an average of two children per family - the world population would continue to grow due to inbuilt population momentum. The United Nations Population Division expects the world population to level out at 10.9 billion people by the end of the century. There are no guarantees this will happen. Population growth is not on the agenda and continued population growth is inevitable unless war and/or nature intervenes. 


A measure of affluence is the consumption of energy and materials per capita and GDP is a good proxy of consumption. GDP per capita has been increasing exponentially, especially in the well-developed countries. The impact of technology on the environment has undoubtedly increased in parallel with increases in consumption. Increases in pollution is just one of many examples.


A measure of affluence is the consumption of energy and materials per capita and GDP is a good proxy of consumption. GDP per capita has been increasing exponentially, especially in the well-developed countries. The impact of technology on the environment has undoubtedly increased in parallel with increases in consumption. Increases in pollution is just one of many examples. 


Given that the world population will continue to increase over the next number of critical decades, the only way we can mitigate the impact of climate change and avoid exceeding planetary boundaries is by reducing our current levels of consumption and the impact of our technology on the environment. In a transition from fossil fuels to renewable energy and infrastructure and beyond, we need to live within our planetary boundaries. It is imperative that we target Zero Population Growth as soon as possible otherwise all our efforts will be in vain. We need to reduce our levels of consumption, especially in the well-developed countries. We also need to adopt benign technology which has a lower impact on the environment. The level of unavoidable waste we generate needs to be such that it can be safely assimilated by the environment.



Figure 2: Current Impact on the Environment and Required Transition