The more relevent population figure for our purposes is the number of people per square mile of land surface. If this is less than one, for example, then we might hope that any changes due to man would be negligible or very slow. If the number is significantly greater than this, there would certainly be the potential to change the planet as part of the normal course of living.
For a population of 6.5 billion we can easily calculate the average number of people per square mile. The radius of the Earth is about 4000 miles, giving a surface area of 4*pi*4000*4000 sq miles. About 1/3 of this area is land, giving about 65,000,000 sq miles of land area. Taking the population as 6.5 billion gives an average of 100 people per square mile over the whole planet. With such numbers, it would seem surprising if man were not significantly altering the ecology of the planet, including the climate. This conclusion supports the view of (most of) the scientific community, that there is a 90% probability that man is a major contributer to global warming.
We can take little comfort from expected population levels or energy usage in the future. By the year 2030 the world population is predicted to grow to 8.5 billion, or to about 125 people per square mile on average. Meanwhile if we take no action, the global energy requirement is expected to rise by 50%. However, neglecting such future predictions with their element of uncertainty, what action is required to at least stabilise the carbon dioxide level in the atmosphere at close to its present level of about 380 parts per million ?
The atmospheric carbon dioxide level at the present time is increasing at about 1.4 parts per million per year by volume. This rate is equivalent to something over 2 parts per million by weight (because carbon dioxide is heavier than air). To calculate the amount of carbon dioxide this represents we need the total mass of all the air in the atmosphere, which is easy to calculate. It is simply the pressure at the Earth's surface times the surface area of the Earth. That is the total mass is about 5000 million million tons or 5x10^18 kilograms. The amount of carbon dioxide in 1 millionth part of the atmosphere is then about 5 billion tons of which carbon forms a fraction 12/44, that is 1.3 billion tons. Thus with an annual increase of 2 parts per million, approximately 2.6 billion tons less of carbon (oil or coal) would have to be burnt every year to stablise the level at the current value.
The total world consumption of carbon fuels is about 8 billion tons. The requirement then is to reduce the combustion of carbon fuels by about a third in global terms to stabilise the atmosperic carbon dioxide level. However, the developing countries of the world are arguing that the problem is not theirs and that the developed countries should cut their excessive carbon dioxide production first. If we then assume that the allowable carbon dioxide production should be based on a countries population, the effect of complying with this depends critically on the particular country, with some countries having to make no adjustment and others needing a large reduction.
The main producers of carbon dioxide in millions of tons and as a percentage of world production, are given by
Country . . CO2 M.tons . . % world O/P . . population (millions)
USA . . . . . . . 6928 . . . . . . 20.6 . . . . . . . . . 300
China. . . . . . . 4938 . . . . . . 14.8 . . . . . . . . 1300
Russia . . . . . . 1915 . . . . . . . 5.7 . . . . . . . . . 142
India . . . . . . . 1884 . . . . . . . 5.5 . . . . . . . . 1169
Japan . . . . . . .1317 . . . . . . . 4.0 . . . . . . . . . 128
Germany . . . . 1009 . . . . . . . 2.9 . . . . . . . . . . 82
Brazil . . . . . . . . 851 . . . . . . . 2.5. . . . . . . . . 187
Canada . . . . . . 680 . . . . . . . 2.1 . . . . . . . . . . 33
UK . . . . . . . . . 654 . . . . . . . 2.0 . . . . . . . . . . 62
Italy . . . . . . . . .524 . . . . . . . 1.6 . . . . . . . . . . 59
Most important are the countries near the top of the list. The top 5 produce over half the global CO2, headed by the USA. The population of the USA is about 300m or about 4.5% of the Earth's population. Thus the required reduction based on population is then not to 2/3 of current output, but to 1/6th ! With China the problem is different. With a population of 1.3 billion or 20% of the world population, on a output of 14.8% it is slightly in excess of the required figure for a 1/3 reduction. However the main problem is the rapid increase in the output, giving an increase in global CO2 from China of between 1% and 2% per year. The current value may well be approaching 20%, requiring no more increase and a 1/3 reduction. The required reduction fractions for Russia, India and Japan are 1/4, 2 and 1/3 respectively. Note that India is only producing half what it would be entitled to.
We consider in more detail the requirements of the UK. With near 1% of the worlds population and 2% of the worlds CO2 production, then based on per head of population, the UK reduction needs to be to 1/3 (similar to Japan). A reduction to 2/3 of the current output might be achievable with difficulty. It might be achieved for example by producing 1/2 the electricity with nuclear power (needing about 30 power stations) and 1/4 from renewables (Seven barrage 6% plus about 10,000 wind generators), plus the introduction of biofuels and other restrictions. However a reduction to 1/3 the present CO2 production would require a much more radical solution and it is unclear how such a reduction can be achieved in an acceptable manner.
A country which does not appear in the top 10 for CO2 production is France. Its reliance on nuclear energy for 80% of its electricity production puts it in a favourable position regarding CO2 production. Could nuclear power be the answer, or is this too high a price anyway ?.
The global production of CO2 by the various activities is given approximately by
Electric Utilities . . . . . . . . . . . . . . 33%
Industrial & Commercial . . . . . . . 25%
Road & non-road vehicles. . . . . . 24%
Agriculture . . . . . . . . . . . . . . . . . . 8%
Residential . . . . . . . . . . . . . . . . . . 7%
Aircraft . . . . . . . . . . . . . . . . . . . . .3%
Hence to achieve a 30% reduction, a large reduction in the CO2 production from electrical utilities and/or road vehicles is essential.
One kilogram of carbon when burnt will give you up to 14 kWh of electrical power. Then a 1500 MW nuclear power station saves about one million tons of carbon per year at full load. Thus you would need at about 2600 nuclear power stations to replace coal, oil or gas power stations just to stablise to atmosphere at it present level, assuming no other increase in carbon fuel burning. Alternatively you would need about 3 million large wind generators to achieve the same effect. Unfortunately it seeems unlikely that technological advances will be enough to give a better solution to the problem in the timescale available. If man is the cause, there would appear to be little chance of the world taking sufficient action in time to avoid major change in the weather patterns, with all that that means. The predictions of future world population numbers may well be in error and not for the happiest of reasons.
The author welcomes comment or reasoned disagreement
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J A C K @ J A C K P I K E . C O . U K