Even the IPCC doesn't claim human-induced climate change until the 1950s. The amounts of CO2 added to the atmosphere didn't seriously ramp up until after 1950.
"It is very unlikely that climate changes of at least the seven centuries prior to 1950 were due to variability generated within the climate system alone. A significant fraction of the reconstructed Northern Hemisphere inter-decadal temperature variability over those centuries is very likely attributable to volcanic eruptions and changes in solar irradiance, and it is likely that anthropogenic forcing contributed to the early 20th-century warming evident in these records." - http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-...