Not at the speed right now, and if it weren't for us adding IR reflecting gasses to the atmosphere we would be in a cooling phase.

That is the simple physical effect. Some trace gasses, like CO2, Methane and water vapour (among others) reflect infrared energy but let the rest of the energy spectrum pass. As Sunlight hits the Earth part of the infrared wavelength is reflected back into space. Most of the energy passes through. The Earth reflects some of the sunlight, but in that process the light is shifted more towards the IR - and the more trace gases are in the atmosphere the more that reflected shifted towards IR right bounces between them, staying in the atmosphere for longer, and in that process heating it up, before, eventually, finding a way out to space.

That is - basic energy transfer and quite simple Physics. So far we assume that Eustice Foote was the first to uncover it - so, we understood since about the 1860s. https://physicstoday.scitation.org/do/10.1063/pt.6.4.20210823a/full/

We know it is us as the CO2 added to the atmosphere carries a clear Fossil Fuel signature - the isotopic count of Fossil Fuel emission is different than "fresh" CO2 and - and we tried loads - there's no other source than our action for the type of CO2 thats increasing.