But there is evidence indicating that most of the increase in atmospheric levels of carbon dioxide could be from natural sources.
So, asks Alan Siddons from Holden, Massachusetts, why do most climate skeptics tacitly and even explicitly accept that man is the culprit?
Let’s consider some of the available evidence.
1. Carbon dioxide concentrations have been measured at Mauna Loa in the Pacific Ocean since 1957 and over this period have shown a general increase.
2. Over this period there has been a general increase in global temperatures.
3. The change in carbon dioxide concentration with time correlates better with temperature change than with change in human carbon dioxide emissions (see Figures 2 and 3 @ Roy Spencer on how Oceans are Driving Carbon Dioxide, Watts Up with That, January 25, 2008).
4. Large interannual fluctuations in Mauna Loa-derived carbon dioxide “emissions” roughly coincide with El Nino and La Nina events (see Figure 3, ibid)
5. There is a clear and strong relationship between levels of atmospheric carbon dioxide and long-term average sea-surface temperatures as would be expected from the solubility curves for carbon dioxide in water at various temperatures and pressures (see Figure 1 @ Atmospheric Carbon Dioxide Levels Follow Sea Surface Temperatures, Jennifer Marohasy.com/blog, September 16, 2007)
6. Current carbon cycle flux estimates indicate that the annual carbon dioxide exchange between the surface and the atmosphere amounts to 20% to 30% of the total amount in the atmosphere.
7. Natural processes remove an order of magnitude more than the annual increase in carbon dioxide each year, then put it back again.
8. Human generated carbon dioxide is around 3% of the total carbon dioxide flux.
9. The isotope ratio difference between ‘natural’ carbon dioxide and carbon dioxide from the burning of fossil fuels is small and not a reliable indication of the source of an increase in atmospheric carbon dioxide (see Spencer Part2: More CO2 Peculiarities – The C13/C12 Isotope Ratio, Watts Up With That? January 28, 2008)
The above nine points are drawn in part from posts by Roy Spencer at blog site ‘Watt’s Up with That?’ on January 25 and 28, 2008 and also a post by Lance Endersbee at JenniferMarohasy.com/blog on September 16, 2007.
Thanks to Alan Siddons for the discussion and the slide, which is from a Lord Monckton lecture.