New paper finds CO2 rapidly increased during the last ice age: Paper published today in Geophysical Research Letters
Study finds there was an 'Abrupt change in atmospheric CO2 during the last ice age' which occurred 'rapidly, over less than 2 centuries. This rise in CO2 was synchronous with, or slightly later than, a rapid increase of Antarctic temps.' The authors also report 'carbon cycle modeling doesn't capture all of the processes for CO2 variations.'
Thus, rapid increases in atmospheric CO2 have been shown to occur naturally due to processes not captured by climate models.
In addition, temperature rise during the last ice age was found to be synchronous or leading CO2 rise, implying that temperature controls atmospheric CO2, rather than CO2 controlling temperature’