CO2 likely lagged the increase in regional Antarctic temperature
"the increase in CO2 likely lagged the increase in regional Antarctic temperature by less than 400 yr and that even a short lead of CO2 over temperature cannot be excluded.”
They think that the CO2 increase may have occurred only 400 years after it got warmer, but the measurement error is high enough that they can't absolutely prove that the CO2 increase didn't occur before the warming. This is the first paper to cast any doubt on the accepted science that CO2 increases have lways lagged, that is came after warming, not the other way around. It doesn't cast much doubt: Essentially they are saying CO2 increase lagged warming by 400 Years +/- 400years.
This comment was probably inserted to avoid attack from warmists, so they could get their paper published: it just says "this doesn't absolutely disprove AGW."
In nature, CO2 increases always come after warming, as a result of the increase in living things: warming brings an explosion in life, generating more CO2.