The claim that the annual temperature range increases at higher latitudes is a well-established geographical and climatological fact driven by solar radiation geometry and land-sea distribution, so no formal citation is needed.
The claim describes a fundamental climatological truism regarding latitudinal temperature gradients (continentality/seasonality increases poleward due to insolation angles and the moderating effect of oceans at lower latitudes). Because it is a foundational matter of everyday geographic and meteorological observation, it is classified as common knowledge under Step 0.