If SAP increases 4 fold, and temperature also increases, then the increase is partially a temperature increase, overwhelmingly an increase in gas molecules in the atmosphere, but not the entire increase. So to blame the entire increase on just increasing gas molecules would be inaccurate.
When you get to 900k years down in Antarctic ice, which is less than a mile down, there are no more trapped compressed gas bubbles, because the temperature is -200F, and the increased pressure from the weight of 900k layers of ice on top, combine to freeze the gas.
You've been asked for an alternative explanation and have none.
If you could "refute" you would, but you can't...