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Chapter Six - Population Reduction

It is hard to imagine what events would kill off large segments of the population (P in The Kaya Identity).  Many people think that war would be one solution but in fact this has killed relatively few in the past.  World War I, for example, accounted for over 16 million deaths (10m military and 7m civilians) while World War II resulted in 70-85 million casualties (about 3% of the then 1940 world population of 2.3bn).

Leading Causes of Death

New diseases, surprisingly, also kill relatively few.  HIV has so far accounted for 70 million infections (mostly in sub-Saharan Africa) with 35 million deaths.  In 2018 this equated to 770,000 deaths.  Tuberculosis killed 1.6 million.  Influenza 646,000.  Malaria 435,000 each year with a predominance of children, which has motivated the Bill Gates Foundation to focus on this disease.  Poliomyelitis killed 350,000 in 1988 but today accounts for very few mortalities despite its reemergence.  Smoking, the cause of multiple diseases, kills 8 million each year and alcohol kills almost 90,000 per year in the U.S.A. alone (3 million globally).

As temperatures rise, pathogen survival will increase resulting in more disease prevalence such as is being seen with the rise of cholera globally.  Malaria will also kill more.

Annually, suicide accounts for aproximately 1 million people worldwide, and in 2017 more Americans died of a drug overdose (illegal and prescription) than died in the entire Vietnam War.

High Mortalities

For the really high mortalities, the scope must be broadened and the annuls of history must be considered.  Here, plagues are quite instructive.  The Justinian Plague in the first century killed roughly half the Mediterranean population while later the Black Death killed 50 million people in Europe in the 1400s; 60% of the then population.  For the common influenza viruses, between 3 and 5% of the world's population were killed by the Spanish Flu in 1918, which accounted for 50 to 100 million following World War I.

Finally, famines can also kill vast numbers in relatively short periods of time.  Under Chairman Mao, 45 million Chinese died over a four-year period following the promulgation of his Great Leap Forward economic policy in the late 1950s.

To achieve high population reductions of, say, 70%, it is clear that a combination of antibiotic resistant disease, war, famine and unchecked new diseases would be required.  Whilst we may feel relatively safe now in our age of modern medicine and negotiated tenuous peace, obviation of the latter could result in a repitition of bloody periods of history.  For higher population reductions of 90%, nothing short of a global thermo-nuclear war would be needed.  Of course, this risks a 'nuclear winter' and the extinction of mankind; the very thing that we are trying to prevent by reducing CO2 emissions to prevent inimical global warming.

The Malthusian Charge Rebuffed

So far, this analysis is open to the charge of being Malthusian, the economist/preacher of the early 1800s who predicted that the U.K. population was headed for a sharp downwards projection as the ability of land to support the growing population became unsustainable.  Malthus, however, failed to predict or foresee the onset of the Industrial Revolution and the ability of technology to pay ultimately for U.K. food imports.  Now, however, we are not considering an island, the U.K., but rather the whole globe.  And, as we are reminded, 'There Is No Planet B'.

Once solar and wind generation achieves grid parity with coal power, we may well see very high rates of decarbonization in our economies.  By some measures this has already been realised which gives hope.  But in the meantime, we still need to reduce progressively our carbon emissions to meet the 2050 targets with strenuous efforts to 'green' the economy to balance as much as possible a general population reduction.  Although advances in technology might therefore 'save the day' in as yet unseen ways, the point is that we cannot rely on them for our 'salvation' - although they remain important options.


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           F = P * (G/P) * (E/G) * (F/E) = P * g * e * f


F is global CO2 emissions from human sources;

P is the global population;

G is world GDP (Gross Domestic Product) and g = (G/P) the global per-capita GDP;

E is global primary energy consumption and …

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Climate and Weather

Yet it is important to make a distinction between climate and weather.  According to, simple climate definitions include:

1. The composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years; and

2. A region or area characterized by a given climate: to move to a warm climate.

Weather is defined as:

1. The state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.; and

2. A strong wind or storm or strong winds and storms colle…