Well greenhouse gases are often described as a blanket and a blanket doesn't immediately get warm, it take time. I doubt the trickling effect is much different in lag time than sudden pulses, its just gradually increasing the blanket rather than pulling it all on at once. Its still gonna take time for more solar energy to accumulate by bouncing off the trickling in CO2.

In the book plows, plagues, and petroleum, the author uses several factors of humans history to argue that man made climate change was slowly having an impact much before the industrial revolution, which is the common "starting point" for most people and scientists. Althought not as drastic as this sudden increase in fossil fuel burning, they argue that impacts such as deforestion and burning of cropland in early human settlements had a measureable impact on carbon sinks and carbon releases, still enough to start skewing the natural rate of climate change.