It is clear that climate has varied throughout the history of the planet, but it is generally agreed that in the past atmospheric CO2 fluctuations were a consequence of slowly changing climate, in contrast to the present where it is clear that  increased atmospheric CO2 levels are driving, or causing, the most rapid period of climate change on record.  It was during one of those past periods of a warmer, moister climate from about 360 to 300 million years ago (the Carboniferous Period) that vast amounts of plant and animal material accumulated on the earth's surface and were slowly buried under subsequent layers of geologic materials, exposed to pressure and heat, and formed what we call fossil fuels - coal and petroleum.  As we today burn these fossil fuels we are rapidly releasing to the atmosphere vast amounts of carbon that was removed over a period of 60 million years, about 300 million years ago.  By doing so we are simply overpowering the equilibrium of our planetary ecosystems with this "sudden" release of CO2.

If we are to understand "Global Warming" or "Climate Change" we must first have a clear understanding of what these terms mean.

"Global Warming" describes the average temperature of the Earth's oceans, land and atmosphere.  The individual measurements are from a very large, international network of weather observations, and typically averaged on a yearly basis.   In 2007 the United Nations Intergovernmental Panel on Climate Change reported that a 100-year linear trend (1906-2005) of 0.74°C in global temperatures (IPCC. Climate Change:2007, Synthesis Report, Summary for Policy Makers. 2007), with most of the change taking place at the higher latitudes.  While this increase may appear small, it is significant in terms of the planet's atmospheric and ocean currents.  More alarmingly, the rate of temperature change has been increasing as well.  It is also vital to remember that temperature is basically a measure of energy.  The warmer an object, the higher its energy content.  Thus an increase in temperature means that our planetary systems are gaining energy.

"Climate" is a long-term (multi-year), regional summation of weather characteristics.

"Weather"  is what we see today, but also this week, or this year.  We correctly might say that the "weather this week was unusual", or that the "weather this year was wetter than normal".   We do not, and should not, talk about the "climate" today, or this year.  We should likewise not expect the weather today, or this month, to be  proof or disproof  of "global warming" or "climate change".

"Greenhouse effect" describes the atmospheric trapping, or reflection of radiant energy back toward the earth.  Every object (with a temperature above Absolute zero) radiates energy.  We experience radiated energy when we feel the heat from a warm object such as a fire, and when we enter a glass greenhouse during a sunny day.   The interior of the greenhouse which is warmed by the sun,  "re-radiates" a portion of the absorbed energy upwards where it is absorbed by the glass which in turn radiates energy both to the atmosphere and back into the greenhouse, causing increased warming.   Likewise a number of gases in the upper atmosphere absorb energy radiated from the solar-warmed surface of the earth and while allowing some energy to escape to outer space these greenhouse gases radiate most back toward the surface of the earth.   (More detail of this process can be found at:   

Water vapor is the largest component of the greenhouse gases, but water vapor has only a short life span in the atmosphere;  too much and it forms clouds, or rains.  On the other hand, Carbon Dioxide (CO2) is also a potent greenhouse gas and has a residence time in the atmosphere measured in centuries, not days.   Therefore, Carbon Dioxide is a greenhouse gas of concern, while water vapor is not.

Analysis of air bubbles trapped in Antarctic ice provides a record of atmospheric gas concentrations for the past 800,000 years.  These samples obtained from an ice core 2.1 miles deep show that CO2 concentrations ranged between 172 and 300 parts per million (ppm) until the beginning of the Industrial Age.  Since 1900 atmospheric CO2 concentrations have rapidly increased from 300ppm to the present 387ppm.  Methane, an extremely potent greenhouse gas likewise ranged between 350 and 800 parts per billion prior to industrialization,  and currently has an atmospheric concentration of approximately 1,770 ppb.

The relationship between atmospheric CO2 and global temperatures is not exactly linear, as we must also include any variation in the amount of incoming solar energy. Such variation has been primarily caused by the reflection of solar energy by increased particulate matter in the atmosphere.   There have been, for example, periods of global cooling that were associated with the addition of large amounts of "ash" to the atmosphere from major volcano eruptions.  A period of cooling in the 1940's is generally felt to be the result of increased particulate matter in the atmosphere due to the added industrial consumption of coal in support of World War II .  Since the passage by the United States of the Clean Air Act of 1963 there has been a measurable increase in the transparency of the atmosphere and corresponding increase of solar energy received at the earth's surface.  This increased energy input is compounding the impacts of greenhouse gases and thus contributing to global warming.   Some have suggested such schemes as deliberately releasing pollutants from high-flying aircraft, or placing giant reflectors in space,  to reduce incoming solar energy.

The long residence time of CO2 in the atmosphere, and the time that it takes for newly released CO2 to reach the upper atmosphere, means that even if we were to totally halt CO2 emissions today, we would continue to see in increase in atmospheric CO2 levels for centuries.  When we factor in the interaction between the atmospheric, terrestrial and ocean ecosystems recent research increases the the time span of CO2 associated climate change to millennia, even with an immediate halt of emissions.  If we also include the effect of a cleaner atmosphere, predicted temperatures rise even more rapidly with estimates in the 2.5 to 3.5°C degree Centigrade range by the end of this century, in contrast to the .74°C cited above for the last century.


An excellent overview of Climate Change physical science can be found on the IPCC site as a FAQ to the 4th Assessment Report.  It can also be downloaded as a brochure.   While it should be noted that on the basis of current data the projections in this 2007 report are now often considered as too conservative these FAQs provide an outstanding overview of scientific basis of Climate Change.