Short answers, pulled from the story.
Radiative forcing is the change in the net downward-minus-upward energy flux through Earth's atmosphere, expressed in watts per square meter, caused by an external driver such as a greenhouse gas or a change in solar output. It cannot be measured by a single instrument directly; scientists calculate it from fundamental physics principles using atmospheric observations and satellite data.
Human-caused radiative forcing reached 2.72 watts per square meter in 2019 relative to 1750, according to the IPCC. This warming is mainly due to increased greenhouse gas concentrations, partly reduced by cooling from increased aerosol concentrations.
Carbon dioxide has the largest individual impact on total radiative forcing. The five major greenhouse gases, water vapor, carbon dioxide, methane, nitrous oxide, and ozone, account for about 96% of the direct radiative forcing from long-lived greenhouse gas increases since 1750. The remaining 4% comes from 15 minor halogenated gases.
From 1979 to 1989, a CO2 concentration rise of 16.0 ppm added 0.248 watts per square meter of forcing. From 2009 to 2019, a rise of 23.6 ppm added 0.316 watts per square meter. The logarithmic relationship between CO2 concentration and forcing means each additional unit of gas has a progressively smaller warming effect, but faster concentration growth has more than compensated.
CERES satellite data showed that anthropogenic radiative forcing at the top of the atmosphere rose by positive 0.53 watts per square meter between 2003 and 2018, with an uncertainty of plus-or-minus 0.11 watts per square meter. About 20% of that increase was linked to a reduction in atmospheric aerosols; the remaining 80% was attributed to rising greenhouse gas concentrations.
Solar irradiance at Earth's orbital distance averages about 1361 watts per square meter, but its decadal variations are small. The 11-year sunspot cycle produces TSI fluctuations of only about plus-or-minus 0.05%, contributing a modest net forcing on climate. The IPCC's 2.72 watts per square meter of human-caused forcing since 1750 substantially exceeds what changes in solar output have contributed over the same period.