It does. Looking year over year, the amount outputted by fossil fuel burning and cement making (a well measured quantity) is about double the increase measured in the atmosphere (also a well measured quantity). There is simply no other explanation than nature absorbs about 1/2 of what man generates. The main caveat is that nature fluctuatesl; during NH summer nature absorbs more than man generates and NH winter where nature absorbs a lot less.
There are some things that the catastrophic AGW people don't have right, such as how long it will take for CO2 to return to "normal" (280 ppm which is probably too low anyway) if man stopped producing CO2. The best estimate is about 40 years to get 1/2 way back to 280ppm from whatever level we are at. So even if our increase in CO2 were a big deal (IMO it is not), it would not be a lasting effect.
Explain what you mean when you say man made CO2 contributes in a meaningful way to overall CO2.
At the current (~$15/94# sack) price of a sack of cement, I'm about ready to buy some coal (or coke some of my beetle-killed timber into charcoal) and burn some of our limestone.
If the Romans could do it, I should be able to.
That might be true if man were the only generator of CO2. Consider this alternative hypothesis.
The earth gradually warms because of a more active sun. That temperature rise affects some of the natural processes that absorb or desorb CO2. Higher water temperatures at the sea surface near the equator could well increase the rate at which CO2 is released from the sea while warmer sea temperatures at near the poles cause less CO2 to be absorbed by the ocean.
That has been proposed as a mechanism to explain why CO2 peaks in ice cores follow temperature peaks by many hundreds of years. Dissolved CO2 is transported from cold waters near the poles to equatorial waters by very slow deep water currents that take hundreds of years to go the distance.
In such a case CO2 levels are not the driver of global temperature but the result of fluctuating global temperatures, and imbalance in CO2 absorption/desorption rates would be the norm for much of the time.
There could be other mechanisms at play here that also affect CO2 absorption and desorption. Perhaps higher temperatures cause CO2 to be released by clathrate structures (hydrates) in the seafloor sediments or in similar clathrates on land in cold regions. This greater release of CO2 could greater than the sea and the flora can absorb, so the CO2 levels go up in the atmosphere.