Since pre-historic man discovered fire the natural CO₂ cycle has been altered. However, as pre-historic man presumably burned contemporary organic matter, rather than fossil fuels, and his actions were limited, the global ecosystems were able readily able to buffer any added CO₂ without any perceptible alteration the atmosphere. However with the development of machinery at the dawn of the Industrial Revolution, human utilization of both contemporary and fossil fuels for energy rapidly exploded, releasing CO₂ into the atmosphere faster than the global ecosystems could adapt.

Figure 1.⁽¹⁾ shows the rate of CO₂ , expressed as metric tons carbon, additions to the atmosphere by mankind since the beginning of the Industrial Revolution. Note until the early 1900's virtually all of the CO₂ emissions came from the combustion of coal. The Ford Motor Company introduced the first assembly line produced automobile, the famous Model T, in 1908 and petroleum combustion soon became a major contributor of CO₂ to the atmosphere.

Figure 1. Carbon emissions from various sources.

Since the beginning of the industrial revolution the concentration of CO₂ in the atmosphere has increased from about 280ppm to 370ppm, and is currently increasing at a rapid rate, as are other greenhouse gases.

Of equal concern is the "residence time" of atmospheric carbon dioxide, or the length of time that added CO₂ will remain in the atmosphere. In contrast to most of the other greenhouse gases, carbon dioxide has an extremely long residence time in the atmosphere. Precisely how long has so far proven impossible to measure with a high degree of accuracy. It is very highly probable that some individual CO₂ molecules released at the beginning of the industrial revolution are still in the atmosphere. On the other hand, others have been very rapidly removed. However, consideration the fate of individual molecules is highly misleading, as the entire system, or carbon cycle, must be evaluated. The combustion of fossil fuels adds additional carbon to the entire contemporary, dynamic system, more carbon in the oceans, forests, soils and indeed more carbon dioxide in the atmosphere. When carbon dioxide is added to the atmosphere, it may be removed by a sink, such as photosynthesis of plants, but it will be replaced from another sink/source, such as soils or the oceans. Thus the entire contemporary system tends to remain in balance, but the overall CO₂ content has been increased by the addition from fossil sources.

An appreciation of CO₂ residence time is essential to any comprehension of global climate change. The core of the problem is that we are taking CO₂ that was sequestered in the earth in geologic time and placing it into the modern ecosystem. Figure 2 .^{(2 )} provides a graphic overview of the impact upon global climate of this mass movement of carbon into our environment. It should be obvious, that even if we were to totally cease fossil fuel

combustion, the concentration of CO₂ in the ecosystem will not stabilize during the lifetime of any living human, but rather only in hundreds of years, and at a level generally estimated in the neighborhood of 1,000ppm or approximately 3 times the level at the beginning of the industrial revolution. CO₂ levels will then continue at greatly elevated levels for thousands of years, being lowered only by geologic processes. Temperatures, climatic disturbances, sea levels and other impacts of climate change will also continue to increase for thousands of years resulting in a totally different environment on earth than that of today.

1.) This figure is from Robert Rohde's amazing collection of Global Warming Art and has a reference link of: http://www.globalwarmingart.com/wiki/Image:Global_Carbon_Emission_by_Type_png

2.) IPCC, 2001: Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Watson, R.T. and the Core Writing Team (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 398 pp. (on-line edition)