Catastrophic man-made global warming advocates have claimed that while this may have been the case in the past, since 1975 the warming has been caused by, and therefore preceded by, increases in atmospheric CO2 due to man's use of fossil fuels. However, actual evidence that the general temperature increase since 1975 was actually caused by increases in atmospheric CO2 was severely wanting.
So has the recent increase in atmospheric CO2 preceded or followed the recent increase in temperature? A relatively recent paper by Humlum, Stordahl, and Solheim entitled The phase relation between atmospheric carbon dioxide and global temperature published in Global and Planetary Change, Vol. 100, January 2013, p. 51-69 answers this question.
They found that since 1982, atmospheric CO2 concentration changes lagged:
- global sea surface temperature changes by 11 to 12 months.
- global surface air temperature changes by 9.5 to 10 months.
- global lower troposphere temperature changes by 9 months.
Figure 1. The upper panel plots the 12-month change in CO2 (NOAA, green) for each month minus that same month 12 months earlier compared to the same 12-month change in sea surface temperature (HadSST2, blue) and the 12-month change in global surface air temperature (HadCRUT3, red). The lower graph plots the difference of a 12-month average with the previous 12-month average for the same CO2 concentration, sea surface temperature, and global surface air temperature series. It is clear that the changes in CO2 come after the changes in temperatures.
If atmospheric CO2 increases lag temperature increases both in the recent warming since 1982 and warming periods over the last 400,000 years, then increased CO2 in the atmosphere is caused by the warming. There is no case for the hypothesis that increased atmospheric CO2 is the cause of warming.
Adding this observation to the failure of temperatures to increase over the last 13 years even as atmospheric CO2 concentrations have increased must be very disturbing to the climate alarmists. The settled science of catastrophic man-made global warming due to CO2 emissions is becoming so unsettled that we have to conclude that the hypothesis has failed. That it has failed comes as no surprise given the basic physics of the climate which I have recently explained here.
There is no case based on climate catastrophe for forcing man to stop using reliable and inexpensive fossil fuels in favor of unreliable and very expensive energy sources such as biomass, wind generation, and solar photovoltaic or concentration plants. This is no excuse here for destroying the coal industry and killing coal-fired power plants, discouraging oil pipelines and drilling for oil and natural gas, and condemning commercial and residential consumers to spending much more on energy that is much less reliable.