I don't remember what season it was when I started commuting but it was a December when I resumed bicycling after a long pause. Riding in the cold seemed easy to me then until the snow and ice came, and it was harder to adapt to the warmer weather as I ran out of layers to remove as it warmed up in the spring. Commuting in the cold is still easier for me, I'll take the tradeoff of more time to get dressed over more sweat any day.