thats so true, i notice the same for myself. its even more evident when you look at the diets of south american and african cultures. both of these continents, especially those with hotter climates generally have fruit and water as staples in their diets, along with various uncooked beans, lentils and such.
not sure about scientific evidence but could be due to the fact that when temperatures are warmer, our bodies want to conserve energy as much as possible because its been trained to live for survival. hotter climates generally mean we are in some sort of famine-based environment, therefore conserving energy and burning less food, which means burning more muscle (after fat stores are depleted)because its the most condensed and longest lasting energy source. our bodies were not built to have much muscle thats why its easier, for most, to get fatter then more muscular.
thats why diet is even more crucial in summer, you dont want to lose hard earned muscle.
also the cold brings about seasonal affective disorder, mild depression that leads to eating more.
i dunno, just some hunches. hope it helps!