The modern U.S. extreme temperature changes occurring under high atmospheric CO2 levels are insignificant, compared to those that happened under low global CO2 level conditions - below 350 ppm
(click on image to enlarge)
Expanding on previous 'C3' articles, here and here, this new chart reveals, record-setting U.S. maximum and minimum temperatures occurred with much more frequency prior to the large influx of human CO2 emissions.
The decades prior to the 1960's produced 84% of the hot maximum, record-setting temperatures; for the same decades, they produced 62% of record-setting cold temperatures.
And despite the much higher atmospheric CO2 levels, the 21st century is not producing the IPCC-predicted, record-setting temperatures, be they high or low.
Look closely, since 1999, zero hot record-setting U.S. temperatures have happened; but wait......OMG, one new cold extreme temperature, in one single U.S. state was confirmed!
Of course, the U.S summer of 2012 has been a hot and dry one for major regions of the country, and new maximum state records will likely happen. But frankly, per the chart, it appears the U.S. was long overdue for a sizzling summer of records and thus the probability for it to happen was high, regardless of CO2 levels.