For those that believe that CO2 is the driving force of climate. I would like to show what happened to the Earth 120,000 years ago at the end of the Eemian Interglacial. That period is almost exactly what the projected world will be like if global warming happens. Understanding what it was like and what happened 120,000 years ago is helpful to know what the future holds for the Earth now.
Cause and Effect. No issue is more turned upside down in the global warming debate than global temperatures and CO2 levels. That CO2 levels change during the past glacial and interglacial periods is very well documented. It has been used as the basis for climate sensitivity calculations by many warmists. There is one problem with determining the climate sensitivity based on CO2 feedback forcing. It assumes that at least some of the temperature change is caused by changing CO2 levels.
If both of those are correct, then the temperature of the Northern Hemisphere (NH) should be shown to be warmer in the past than it is now. A recent paper (Sundqvist, Zhang, Moberg 2010) says just this. It focuses on the two time periods of 6,000 and 1,500 years ago and uses 104 temperature reconstructions from around the Arctic region to determine the temperature at those two times. It also provides some results for the differences between 6,000 years and 500 years ago. Due to limitations in the data the overall results are for the 6,000 and 1,500 years ago.
Understanding local changes in temperature and energy is often critical to understanding the Earth’s climate. Such analysis is usually ignored. That is one important reason that the climate sensitivity is routinely overstated. The current geography of the Earth is such that the changes in energy to the Northern Hemisphere are the most significant aspect to understanding the Earth’s climate.