Are human activity-generated CO2 emissions a significant cause of global warming? During the 250 years since the Industrial Revolution began to get up steam, average carbon dioxide (CO2) concentrations in the atmosphere have risen from 280 to nearly 380 parts per million (ppm). This is 27% higher than the highest levels found in air bubbles trapped during the last 650,000 years in East Antarctica ice cores. Conventional climate scientists attribute the majority of the rise to human activities, principally the burning of fossil fuels (oil, gas and coal, the manufacture of cement), and the clearance of land for agriculture.

They argue that there are two strong reasons for blaming human activity:

• CO2 concentrations in the atmosphere between 1006 and 1978 AD have bobbed between 274 and 280ppm, [1] then risen more rapidly than could have been caused by natural factors like higher energy from the sun
• Oxygen levels in the atmosphere and oceans are reducing increasingly rapidly, probably due to the burning of fossil fuels (which also burns atmospheric oxygen) and land clearance for agriculture (trees and plants emit oxygen)

Some add a third - that the profile of CO2 from burning fossil fuels, trees and scrub is subtly different from that of atmospheric CO2. It contains, apparently, slightly lower levels of the carbon isotope 13C, altering its carbon isotope 12C/13C ratio. Some scientists have detected significant rises in low 13C CO2.

Others dismiss the value of this discovery on the grounds that low 13C ratio CO2 is not, as suggested, unique to CO2 from human activities. They claim that the respiration and decay of land and ocean animals and plants emit CO2 of the same 12C/13C profile as the burning of fossil fuels, etc.

Ed.- In fact, none of these ‘strong reasons’ often quoted by conventional climate scientists proves that human-caused carbon dioxide has (i) significantly increased CO2 concentrations in the atmosphere (there could be other significant as yet undetected sources) or (ii) that it is contributing significantly to global warming. They only prove that it is there.