- the global climate is changing
- carbon dioxide content of the atmosphere is increasing due to human industrial activity
- the increase in CO2 concentration increases the amount of heat trapped in the atmosphere
- this could cause a runaway effect making the earth uninhabitable
But what if one of those principles above is wrong? What if CO2 concentration is not correlated to average global temperature? What if the current variation is in fact insignificant?
The glaciers of Greenland have yielded thousands of ice core samples to scientific survey. Significantly, the Oxygen-18 isotope concentration in the ice is a good proxy for average global temperature over a long timescale. A water molecule containing O-18 is 11% heavier than the O-16 water molecule, so it takes more energy to get a water molecule containing O-18 to evaporate into the atmosphere than it does for O-16. This heavier isotope is more abundant in the snow when the temperatures are warmer, and less abundant when it is colder globally. The ratio of O-18 to O-16 in the ice corresponds to a temperature at ancient glaciers in Greenland - a yearly average high-resolution record going back over 100000 years.
Dr. Don J. Easterbrook has an analysis of these ice core samples, analyzing the rates of change of temperature:
Temperature changes recorded in the GISP2 ice core from the Greenland Ice Sheet show that the magnitude of global warming experienced during the past century is insignificant compared to the magnitude of the profound natural climate reversals over the past 25,000 years, which preceded any significant rise of atmospheric CO2. If so many much more intense periods of warming occurred naturally in the past without increase in CO2, why should the mere coincidence of a small period of low magnitude warming this century be blamed on CO2?So that about does it for anthropogenic global warming.
Update: Here's another view, looking at ocean sediments, providing a temperature reading dating back 65 million years. And here is the GISP2 data; see for yourself.