The discussion and analysis here should be readily understood by most readers, but some of the theory and interpretation behind the discussion might require some understanding of relatively low-level chemistry. 

The stable forms of carbon at the Earth’s surface are: carbon dioxide CO2, bicarbonate ions in solution HCO3-, carbonates (calcite, limestone etc). These three are the most oxidised and therefor the most stable forms of carbon at the Earth's well-oxygenated surface. Other forms of unstable carbon are more reduced and include methane (CH4), carbon monoxide (CO), elemental carbon it self, and living matter. All of these will ultimately oxidise to one of the more oxidised variants in the presence of an oxygenated atmosphere.   

CO2 is the most oxidised form of carbon, forming a stable relatively inert gas in the atmosphere (currently just over 400 ppm). Bicarbonate (HCO3-), is the stable form dissolved in water, which contains 60 times more abundant CO2 than does the atmosphere.  Carbonates are the stable solid form, mainly as calcite (CaCO3 or limestone) and dolomite (CaMg(CO3)2 another form of limestone). Limestones are 44% CO2 by weight and form a major rock type, often entire mountain ranges. More than 99% of all the CO2 component formerly in the Earth’s early atmosphere is now locked up in carbonate rock.   

Atmospheric CO2

Certain trace gases in the atmosphere are thought to maintain the Earth’s temperature at a fairly constant level. These gases are called greenhouse gases & have the effect of preventing incoming visible radiation escaping as infrared radiation. The trapped radiation wave lengths heat up the atmosphere at the surface, but only to a limited extent, dropping off dramatically as their abundance increases (see later comments).

The mean global temperature of the Earth is a warm 15 degrees C . Without these greenhouse gases, all infrared radiation would be lost to space and the global Earth temperature would be considerably lower overall with hot days and very cold nights. Without the atmosphere the Earth’s mean surface temperature would be -18 degrees, rather than the present average of 15 degrees. Variations in greenhouse gases are thought to influence climate, & in the present climate debate CO2 is the greenhouse gas of principal concern.

The main greenhouse gases, their abundance, their thermal influences & the contribution by man are presented in the following table.

Ranking of greenhouse gases vs CO2 in terms of global heat generation capacity:

GREEN HOUSE GAS                                    Heat retention potential (multiple)
Carbon Dioxide (CO2)                                 1
Chloroflourocarbons (CFC’s)                     1,300 TO 9,300
Methane (CH4)                                             21
Nitrous oxide    (N2O)                                 310

Water vapour (this does not include water droplets as in clouds) is a powerful greenhouse gas comprising about 95% of the greenhouse gas inventory & is by far the dominant influence, but does not contribute to what is called the enhanced greenhouse effect because it is not increasing in abundance.
A runnaway greenshouse effect is said to occur when increasing greenshouse temperatures are enhanced by positive feedbacks in the environment that also generate more greenhouse components or other forms of atmospheric temperature increase, (eg increasing water vapour) thus accelerating and exacerbating the climatic effect. Positive feedbacks are generally more than compensated by buffering effects which act to minimise any change in systems at equilibrium.

Pre industrial revolution levels  1750-1800                        1990 levels

              CO2                       280   ppm                                           353 ppm
              Methane                 0.8 ppm                                          1.72 ppm

CO2 dissolved in the ocean is some 60 times that in the atmosphere with more than 85% as bicarbonate ions (HCO3-).

Human activity (fossil fuels & burning biomass), has caused much of the increase. Volcanic gases also produce large amounts of CO2. Burning all the fossil fuels in existence would produce an atmospheric CO2 level of around 2000 ppm. To halve the present levels would probably annihilate all terrestrial vegetation & animal life. Decreasing atmospheric CO2 would be far more disadvantageous than increasing it. Methane is sourced through rice cultivation, ruminating animals, coal mining, natural gas venting, & inefficient biomass oxidation.

95% of warming due to greenhouse gases comes from water vapour in the atmosphere (not water droplets as in clouds), and only 0.28% from human additions. Human activity accounts for about 6% of the non-water vapour component.  

Atmospheric CO2 levels over recent time, temperature cycle regularity and warming pulse rates 

The chart below displays the cyclical variations in atmospheric CO2 determined from ice core samples over the last 400,000 years, showing the ”hockey stick effect”, & the remarkable regularity of CO2 increases & reductions following 100, 000 year cycles. If CO2 causes temperature increases, what caused these regular cycles of increasing CO2 lasting about 100,000 years? If however the temperatures where cyclical (due to Milankovitch-cycle style planetary orbit, tilt and wobble variations), and the CO2 variations followed temperature changes (not driving them), this would account for this phenomena.  

A similar chart shows temperature data from Antarctic ice cores (EPICA C Dome) over the same time interval. The major warming peaks (indicated by the black arrows) are about 100,000 years apart and reflect about 8 degrees of warming. The present position on the larger zig-zag pattern suggests we are about to descend into a 100,000 year global cooling event, representing some 8-10 degrees of cooling. 

The much smaller peaks are some 1000 years apart and reflect 1-2 degrees of warming. The smaller peaks from the Greenland Ice Core data chart  ( refer to the 10,000 year Greenland ice core GISP2 chart below), show 1-2 degree, warming over 100-200 years indicating a warming rate of around 1 degree per hundred years in keeping with present warming estimates for the current warming pulse determined elsewhere by climate science sources. The consistent warming slopes on these shorter cyclical warming pulses suggest that the warming rate it fairly consistent in these 1000 year events, whose regularity suggests a very short-term (1,000 year) minor orbital cyclicity perhaps not previously recognized.  

Some 10 major warming & cooling cycles in the GISP 2 Greenland ice core are scattered regularly over the last 10,000 year interglacial warming episodes.  

Calculating global temperatures & warming & cooling rates from Greenland ice core data for warming cycles over the last 10,000 years. The warming appears generally about 2 degrees over about 200-300 year warming event. Warming & cooling appear symmetrical at about 2 degree/100 years for the higher peaks and 1 degree per 100 years for the shorter peaks. 

Other significant CO2 and temperature versus time charts across all of geological time are presented and discussed in much more detail elsewhere in this web site.


Of the over 200 billion tons of CO2 that enter earth's atmosphere each year from all sources. Human activities—mostly burning of coal and other fossil fuels, but also cement production, deforestation and other landscape changes—emitted roughly 40 billion metric tons of carbon dioxide in 2015. Approximately 90 billion tons come from biologic activity in earth's oceans and another 90 billion tons from such sources as volcanoes and decaying land plants. According to the U.S. Geological Survey (USGS), the world's volcanoes, both on land and undersea, generate about 200 million tons of carbon dioxide (CO2) annually, while our automotive and industrial activities cause some 24 billion tons of CO2 emissions every year worldwide:
                             › article › earthtalks-volca..

At 382 parts per million, CO2 is a minor constituent of earth's atmosphere—less than 4/100ths of 1% of all gases present. Compared to former geologic times, earth's current atmosphere is CO2 impoverished. During the Ordovician-Silurian glaciation (450-420 million years ago),  atmospheric CO2 was more than 4000 ppm, but did not contribute to any warming. During the Jurassic-Cretaceous glaciation (151-132 million years ago), atmospheric CO2 was more than 2000 ppm and again did not contribute to any warming. If CO2 drives climate, why were there glaciations and not a runaway greenhouse effects during these events? 

The effect of increasing levels of atmospheric CO2 on plant growth and animal health.

The photo below shows a comparison of plant growth achieved in atmospheres of differing CO2 levels. This readily displays the fertilizer effect of increased levels of atmospheric CO2. The numbers in the photo's indicate the amount of additional CO2 that has been introduced into the atmosphere, and the numbers below the total atmospheric CO2 content in parts per million.

The table and chart below display the dramatically decreasing greenhouse warming effect of increasing CO2 levels in an atmosphere, a point that is often lost when increasing CO2 levels are being discussed in the media.  The data suggests that plants are seriously starved for adequate CO2 for healthy development and optimum growth in the present atmosphere and that significant agricultural productivity may be gained in this area if atmospheric CO2 levels can be substantially increased. Optimal levels of atmospheric CO2 may be around 1000 ppm for many plant species. At present plants find it difficult acquiring sufficient CO2 from the present very thin, CO2-depleted atmosphere. 

Plants exposed to higher levels of CO2, not only grow more vigorously , they require less water (less evapo-transpiration from smaller stomata required to get adequate CO2). They can grow in drier climates and produce higher yields on smaller acreages. Limiting growth factors such as higher usage of nutrients such as nitrogen, zinc, iron etc (as exist for today''s plants) can be accommodated, as they are today, with  fertilizers, supplements and management practices. There are likely to be pros and cons, with increased CO2 levels, but plants developed and thrived under these conditions in the past, they don't need to adapt to new conditions, and they manage on less water and in drier conditions. Even the small man-made CO2 contributions over the last 50 years or so have dramatically greened the earth (see CSIRO global map below).  

The image below is derived from:  Sherwood B Idso, President of the Centre for the study of carbon dioxide and global change.  Research Physicist with the U.S. Department of Agriculture's Agricultural Research Service at the U.S. Water Conservation Laboratory in Phoenix, Arizona, where he worked since June 1967. His science citation record: as of July 2000, Dr. Idso’s research papers had been cited in the scientific literature in excess of 6,500 times, more than an order of magnitude above the norm for all scientists of that time period.

CO2 & Human Health. 

CO2 is odorless, colorless, tasteless and slightly heavier than air. Plants absorb CO2 and emit oxygen as a waste product. Humans and animals breathe oxygen and emit CO2 as a waste product. Carbon dioxide is a nutrient, not a pollutant, and for all life,  plants and animals alike it is an essential requirement. Atmospheric CO2 is an essential plant fertilizer not a toxin. All animals get their carbon from eating plants, or eating other animals that eat plants. The effect of increased atmospheric CO2 on humans appears minimal at any likely concentrations, even up to 1% (10,000 ppm). Human exhale CO2 at levels of around 38,000 ppm from their lungs, suggesting that even at these levels there is no serious toxicity as long as here is adequate oxygen available for normal respiration. 

Coral reefs and CO2

CO2 gets into the atmosphere originally through volcanic eruptions.  Once in the atmosphere it is continually recycled by terrestrial plant life (through the process of photosynthesis), animal life,  the earth's oceans (in the form of the bicarbonate ion, HCO3-), and eventually into calcite (limestones, coral reef structures, marine shells & skeletons), and carbon energy reservoirs of coal, petroleum & gas.  The oceans contain more than 60 times as much CO2 as the atmosphere and are in equilibrium with marine limestone deposits. 

The great retirement home for most terrestrial carbon dioxide is in limestones (44% CO2 by weight), and they make up a considerable proportion of surface and subsurface rock sequences, including all the worlds coral reefs and entire mountain ranges in many parts of the world. Coral reefs are made of CO2 and would not exist without CO2. The coral organisms themselves derive all their cellular carbon from CO2 sourced  from bicarbonate ions extracted from the oceans, but ultimately derived from he atmosphere.

The carbonate forming chemical reactions depend on the two equilibrium reactions involved:

(1)      CO2     +    H2O      <---->   HCO3-    +     H+  (acid)      at the atmosphere-ocean interface

 (2)      HCO3-   +    Ca2+   <---->   CaCO3    +    H+   (acid)     occurring in shallow warm oceans
 The overall combined  reaction is:

(3)    CO2  +  H2O  +  Ca2+   <------>     CaCO3  +   2H+  (acid)   
Note that although these reactions are equilibrium reactions, the equilibrium strongly favors the reactions moving the the right in each case and downward in the sequence  through 1),  to 2), and the ultimate removal of all CO2 from the atmosphere, and all HCO3- from the seas, to from voluminous limestone. Eventually all the world''s carbon and all the world's CO2 will end up in limestones, (see later section), and none will be available to maintain or form any life on Earth.       

Note also that for each molecule of calcite (CACO3) produced (or molecle of CO2 consumed),  two hydrogen ions (H+,  read acid) are produced, contributing to ocean acidification.  Coral reefs themselves are responsible for much of the worlds oceans acidification, although no one is suggesting that we should eliminate coral reefs in order to reduce ocean acidification. Atmospheric CO2 when dissolving in the oceans to produce bicarbonate ions (HCO3- reaction 1 above), does increase ocean acidification, but the removal of bicarbonate ions to form coral reefs and other limestones (reaction 2 above) produces even more acid.

CO2 in the oceans and ocean acidification 


Carbon dioxide dissolves in the ocean to form carbonic acid (H