Roles of Surface Albedo, Surface Temperature and Carbon Dioxide in the Seasonal Variation of Arctic Amplification

A decrease in surface albedo over ice‐covered ocean leads to global warming and Arctic‐amplified warming. Numerical results indicate seasonal variation in Arctic amplification (AA) is a result of local forcing and feedbacks in the Arctic. A decrease in surface albedo leads to a positive feedback, which dominates the local forcing and feedback mechanism. Ocean heat storage in the subsurface acts as a heat forcing to delay the influence of surface albedo feedback. In summer (autumn), heat storage increases (discharges) and contributes to a negative (positive) heat forcing, which decreases (increases) the positive local forcing and feedback and triggers the occurrence of the minimum (maximum) AA. In addition, increased CO2 forcing largely decreases the outgoing longwave radiation at the surface and increases surface temperatures, especially at low latitudes and in the Arctic winters, which decreases the AA magnitude and seasonal variation, although the AA remains nearly the same during winter. Plain Language Summary The surface albedo over ice‐covered ocean is decreasing, leading to global warming and amplified Arctic warming, which confirms the importance of sea‐ice loss to the Arctic amplification (AA; both formation and seasonal variation). We also study the role of increased CO2 in the seasonal variation in AA by comparing experiments with and without increased CO2, and reveal the direct contribution of CO2 forcing, which is usually neglected. (1) The seasonal variation in Arctic amplification is determined by local forcing and feedback in the Arctic because there is little seasonal variation in the global surface temperature increase and there is nearly no contribution from remote forcing. (2) A positive feedback of surface albedo dominates the radiation flux variation and enhances heat absorption. The Arctic amplification reaches a minimum (maximum) due to the formation (discharge) of heat storage in the subsurface ocean in summer (autumn). (3) Increased CO2 forcing enhances the global surface temperature variation and decreases the Arctic amplification, although it provides a strong positive feedback and nearly keeps Arctic amplification unchanged in winter. Key Points Contributions from CO2 and surface albedo to Arctic amplification (AA) are discussed individually using numerical experiments The seasonal AA variation is controlled by surface albedo feedback and heat storage form/discharge in the subsurface ocean CO2's direct influence weakens AA's mag