Short answers, pulled from the story.
Human activity generated a radiative forcing of 2.72 watts per square meter in 2019 relative to the baseline year 1750. This value represents the net change in downward minus upward radiative flux due to external climate drivers.
Physicists developed comprehensive descriptions of radiative transfer during the first half of the 20th century before applying them to stellar atmospheres. The term gained widespread traction in scientific literature by the 1980s after researchers distilled perturbation frameworks into usable metrics.
Carbon dioxide concentrations reached 415 parts per million by volume in 2019, representing a 50% increase since 1750. This specific rise corresponds to a cumulative radiative forcing change of plus 2.17 watts per square meter.
Milankovitch cycles span periods of 40,000 to 100,000 years involving changes in orbital eccentricity and axial tilt. Such shifts cause total solar irradiance to fluctuate by about plus or minus 0.2% over these long durations.
Satellite instruments including MODIS and CERES have monitored these values continuously since 1998. Interannual variations of plus or minus 0.07 around the mean albedo occur throughout each year near solar equinoxes.