The lands around the Sea of Tet are generally considered a temperate climate zone, especially in the Cothel area. Lands farthest to the south and beyond the Rim Mountains are more tropical, although the Rim Mountains are generally quite tall and so tend to remain colder at altitude.
Two thousands miles separate the most southern of the known world from the most northern. This puts the northern most countries into the polar zone with shorter summers and harsher winters.
The northern part of the Endless Sea close to land does not remain frozen the whole year, allowing ships to pass around the most northern lands for a couple of weeks at the end of summer. However, the route is treacherous and often filled with icebergs. This keeps those of the most northern countries somewhat isolated from their southern neighbors that border the Sea of Tet. Most countries have trade relationships to allow goods to pass over land, but disputes over taxes and levies have led to many wars through the ages.