So what you're saying is that warming occurs, and then CO2 rises? Apart from the fact that Vostok (for example) stops around 1813, and so can't capture any modern warming (i.e. your argument is invalid in the modern regime), deniers need to find the warming necessary to cause CO2 levels to get to their present levels: "The highest pre-industrial value recorded in 800,000 years of ice-core record was 298.6 ppmv" (taken from http://cdiac.ornl.gov/trends/co2/ice_core_co2.html).
TL;DR: CO2 has been pretty much confirmed as the cause of AGW.