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.

How fucked are we?

They may be thinking of the half-life of C02, around 120 years ... or the delayed effect of temperature uptake by the ocean. I'm not a clime scientist.

Apologies I should have linked a source in that claim. I only had a rough understanding of it and had read an article on phys.org that mentioned that previously. Arguably still a big concern since we could not be seeing the actual warming done in present day 2026 for another decade or more.

Not true at all. Compare:

"lag time before they actually start causing heat" and

"the timing between an emission and the maximum temperature response is a decade on average"

A "start" and a "maximum" are completely different. IR absorption starts immediately and increases over years to a maximum.