Revised 27 September 2021

CONDENSED CHAPTER SUMMARY - see more detailed summaries under Section headings

Critical Thinking

  • Science deals with facts based on hard evidence provided by experiments and analysis.

  • What distinguishes genuine science from pseudoscience is its willingness to allow evidence to confirm or challenge its theories.

  • The challenge of the scientific method is to eliminate personal and subjective influences. Methods of science have been developed to eliminate these influences. One method is the peer review process.

  • The findings of conference papers should be regarded as being tentative and yet to be confirmed by the research community.

  • Some people expect science to provide absolute certainty. This expectation is unrealistic. Some people need and seek certainty in their lives. Pseudoscience panders to this need. 

  • Critical thinking involves the ability to recognise the logical form of an argument, deconstruct that argument, and then evaluate the conclusion.

  • Critical thinking requires practice, effort, and the humility of being prepared to objectively consider claims and arguments of others which challenge one’s own beliefs. 

  • Deduction cannot establish whether a conclusion is true or not as opposed to being logically valid. All that logic can offer is that if all the premises are true, then the conclusion must also be true so long as the conclusion follows necessarily from the premises. If any of the premises is not true, then the conclusion is also not true

  • Deconstruction of an argument is a process of disentangling the chain of arguments into separate sets of premises and conclusions and linking conclusions which form the premises of higher order conclusions.

  • The process of deconstructing an argument involves assessing whether the assumptions of an argument are warranted, the reasoning is relevant and sufficient, and whether relevant information has been omitted or not.

  • The doubling time of any entity which is growing is the time interval over which that entity doubles in size

  • Given steady exponential growth in the extraction of resources, the absolute size of the stock of any resource has very little effect on the time it takes to exhaust the resource. If the original resource were twice as large, it would take only one more doubling time to exhaust the resource. 

  • William Ophuls warned us back in 1977 that the time for concern about the potential exhaustion of a resource comes when no more than about 10% of the total has been used up. So far, this warning has been ignored. 


  • During the 20th century our world population doubled within one lifetime and there are now strong signals that our world population has exceeded the carrying capacity of our planet Earth.

  • Continued increases in population during a transition from fossil fuels to renewable energy can but only result in a Sisyphus like undermining of efforts for a smooth transition. 

  • When a population is growing rapidly, it is more illuminating to focus on changes in the growth rate rather than the population level.

  • The size of the populations in the middle-income countries in 1960 and subsequent annual growth rates have dominated growth in the world population.

  • When forecasting the future size of a population, the changing age composition of the population must be taken into account.

  • In a transition from a growth to a ZPG population, there would be a period of continued momentum of growth in the population called population momentum.

  • At the replacement fertility level, each family on average would comprise of 2.11 children. The extra 0.11 child on average compensates for those children who do not survive to reproduction age and for those women who do not have children by virtue of choice or infertility. 

  • Continued growth in the population of the middle-income countries will dominate future growth in the world population before the year 2100.

  • A decline in the age dependency ratio has the potential to alleviate the burden of the working-age population to support those who are dependents.

  • The United Nations World Population Prospects 2017 Revision states that “with a certainty of 95 per cent, the size of the global population will stand between 8.4 and 8.7 billion in 2030, between 9.4 and 10.2 billion in 2050”

  • Projections are not predictions and are based on many assumptions (Cohen, 2002).

  • Whatever the future holds in store for us, continued growth in the world population before 2100 is inevitable unless dire consequences of climate change, inadequate access to energy be it fossil fuels or renewable energy, political strife, and over-reaching the carrying capacity of a local environment take over.


  • All that current and future generations can do during a transition to ZPG is to be better prepared and become more resilient to change.