Radiative forcing (W/m²) measures the energy imbalance of the climate system. Positive forcing (more energy absorbed than emitted) warms the planet; negative cools it. Accumulated CO₂ since pre-industrial times generates ~+2.7 W/m² forcing.
Aerosols produce a negative forcing (~−1.1 W/m²) partially offsetting greenhouse gas warming. Climate sensitivity indicates how much Earth warms per unit of forcing.