Why does the annual temperature range get bigger where latitude is higher?
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The bigger temperature range is because of the wide difference in the length of daylight seen in the higher latitudes. Depending on how high you are talking about, there can times where there is no sun for a month and vice versa with constant sun. Because of this there will therefore be more time for warmth and cooling as the Sun (or lack thereof) is what drives the diurnal temperature change the most.