What is meant by the term 'net forcing'?

• A. The sum of all individual radiative forcings from different drivers, positive or negative, that shifts the energy balance.
• B. The total greenhouse gas concentration.
• C. The average solar irradiance over a year.
• D. The difference between current and pre-industrial temperatures.

Answer: (D)

Net forcing is the overall change in the Earth’s energy balance caused by all drivers, summed together. Each factor—greenhouse gases, aerosols, land-use changes, clouds, and even variations in solar input—can push the balance toward more incoming energy (warming) or more outgoing energy (cooling). Radiative forcing quantifies how much a given factor alters the energy leaving or entering the system, measured in watts per square meter. Net forcing combines all these individual effects to give the total shift in energy balance. A positive net forcing means a tendency to warm, while a negative one means a cooler tendency. The other concepts describe components or responses (like greenhouse gas concentrations, solar input, or the temperature difference from pre-industrial times) but do not represent the aggregated energy-balance change itself.