1. An increase in the temperature of the lower atmosphere and the surface of the earth ("global warming") is occurring. Observational 'facts'.

  2. The 'Greenhouse Effect' plays a major role in maintaining the temperature of the lower atmosphere and the surface of the earth. Inferred causal links.

  3. The intensity of the 'Greenhouse Effect' is importantly controlled by the total amount of carbon dioxide (CO2) in the atmosphere. The total CO2 content equals natural CO2 plus 'anthropogenic' CO2 (CO2 produced by people's activities). Inferred causal links.

  4. The total amount of carbon dioxide in the atmosphere has greatly increased since the start of the Industrial Revolution, roughly 200 years ago, at the time when people began burning fuels in ever-increasing quantities and deforestation accelerated. Observational 'facts'.

  5. The burning of fuels (wood, coal, oil, natural gas and gasoline) and the cutting down of forests produces (anthropogenic) carbon dioxide, thus increasing the total CO2 content of the atmosphere. Inferred causal links.

  6. As the total carbon dioxide has increased. The temperature of the atmosphere has increased. Observational 'facts'.

  7. The increase in temperature has been caused by an increase in the intensity of the 'Greenhouse Effect' which, in turn, has been largely due to the increase in total carbon dioxide. Inferred causal links.

  8. The increase in total carbon dioxide has coincided with an increase in anthropogenic carbon dioxide. Observational fact.
  9. THUS THE HYPOTHESIS: People's activities are a major cause of global warming. Inferred causal links.

David J. Leveson