In the 800 kyr $\ce{CO_2}$ record, how detectable would a short-term peak be?
$\small\mathsf{CO_2}$ does not fall back quickly:


  graph shows the IPCC 2007 $\small\mathsf{CO_2}$ liftime from a computer model run that shows what happens to a single instantaneous pulse of $\small\mathsf{CO_2}$ emitted to the atmosphere. One thousand years after the $\small\mathsf{CO_2}$ is emitted to the atmosphere 20% is still there according to this model.
  only zero carbon
  


The decline shown is mostly due to $\small\mathsf{CO_2}$ dissolving in the oceans.