Thus, the spatial and seasonal evolution of forcing in the future requires as much scrutiny as the global mean estimate. (ipcc.ch)
ENSO is an phenomena which extends over large spatial area and can have a different seasonal evolution from event to event. (esrl.noaa.gov)
See: Perovich, D. K., T. C. Grenfell, B. Light, and P. V. Hobbs (2002), Seasonal evolution of the albedo of multiyear Arctic sea ice, J. Geophys. (realclimate.org)