Global warming, that is, the generalized warming of the earth surface and atmosphere over the last years is an unquestionable reality. I shall not present here the scientific evidences of the phenomenon because they are easily found elsewhere and are strongly established. Nor shall I discuss the causes of global warming. There is an enormous controversy in this issue. Would global warming be caused by the secular evolution of geological and solar activities or by the cumulative effect of human action in the production of gases, especially, CO2, which would be responsible for the imbalance of the earth greenhouse effect?

Other is my purpose. I present simple quantitative evidences that justify the denying of human action as responsible for the current catastrophe that falls over the humanity. It is obvious that the humanity's predatory activity in the destruction and contamination of the environment must be reduced at any cost. But one cannot immediately attach global warming to such activity. Or, in other words: there are plausible reasons for doubting that human action is the great villain in the phenomenon of global warming. I use simple high school physics and some data from the relevant bibliography to show by means of some numerical figures that human action is small when compared to the magnitude of other actors involved, namely, the planet as a whole, the oceans and the Earth's atmosphere.

Greenhouse effect

CO2 is the only of these gases that is copiously produced by human activities. According to Prof. Nilton José Sousa, from the Federal University of Paraná, Brazil, since 1860 the human beings have launched about 175 Gt (1 Gt = 1 gigaton = 1 billion tons) of CO2 in the atmosphere (cf. www.floresta.ufpr.br/~lpf/efeitoestufa.html and Overview of Greenhouse Gases/US EPA). Incidentally, the Industrial Revolution began in England around 1760. That quantity is little impacted by the production in the first 100 years of the Industrial Revolution.

My working hypothesis is that the human action on global warming can be quantified by 175 Gt of CO2 produced in the last 150 years. CO2 acts making part of the earthly atmosphere, contributing for the greenhouse effect, and dissolved in the ocean waters causing changes in the marine environment. In what follows, I calculate the total mass of the oceans and of the terrestrial atmosphere in order to make a comparison amongst those masses, and then have an insight of the potential magnitude of CO2 produced by human activities.

Oceans and atmosphere

The total mass of the oceans may be calculated by the product of the ocean area × average ocean depth × saltwater density. We know that oceans cover about 70% of the terrestrial surface and that its average depth is approximately 4,000 meters. The density of saltwater is 1.03 g/cm3. The mass of the oceans results then in approximately 1 billion Gt.

The atmosphere exerts pressure over the terrestrial surface that can be easily measured. It is 101,000 Pa, where Pa is the abbreviation of pascal, the unity of pressure in the International System of unities of physical quantities (SI, from the French: Système International d'Unités). Now, pressure is force per area. The force is given by the total weight of the atmosphere and the area is the total area of terrestrial surface. The product of pressure × area of the terrestrial globe is equal to the total weight of the terrestrial atmosphere. From its weight we get its mass which is about 5 million Gt.

A few more figures: the total Earth's mass is 6,000 billion Gt and the total mass of the human population is, currently, equal to 7 billion × 70 kg, or, 0.5 Gt.

All the masses discussed above are listed below, expressed in gigatonnes (Gt).

• CO2 (150 years): 175

• Oceans: 1 billion

• Atmosphere: 5 million

• Planet Earth: 6,000 billion

• Human population: 0.5

All CO2 produced by the human action in the last 150 years represents 0.00002% of the oceans mass and 0.004% of the atmosphere's mass. The human population represents a percentage 2 × 175 = 350 times smaller than those. The mass of the Earth serves to illustrate how the global warming problem is irrelevant to the planet itself, in spite of being a question of life and death to humanity. These figures show that it is perfectly reasonable doubting that human action is the main responsible for the effect. It is worthwhile pointing out that I do not claim having demonstrated that man has no influence in the phenomenon but only that it is reasonable having such a doubt.

How to solve this dilemma? Human action or a phenomenon of the normal planet evolution? The first suggestion that occur to me is the use of a tracer (or marker) of the ambient temperature that is insensitive to human activity, i.e., to the greenhouse effect. The second one is the computer simulation of an environment resembling the terrestrial and submitted to similar mass proportions as discussed above.