Elevation and latitude would be some key points to consider. For instance, the many countries of the western hemisphere are mainly near the equator and nowhere on any of them are there mountains higher than 5,000 feet. The land is low and the terrain is dark, which absorbs and retains heat. There is a huge mountain range that runs north/south along the westernmost coast which creates a massive rain shadow so that everything to the east of it is desert. There's little land north or south of the tropics (if the world is tilted at all on its axis). The many countries have convoluted coastlines, providing lots of inlets and bays that can provide hot, humid, swampy environments. Main rivers skirt the interior of the continents further contributing to their vast inland deserts.

The eastern hemisphere is made of two large land masses, each one located at the poles and extending maybe thirty degrees from the north pole and the same from the south pole. The areas of both land masses that are closest to the equator feature the tallest mountains in the world, in fact most or all of the land that is not in the arctic regions is well above 14,000 to 20,000 feet above sea level. At this altitude, the snow never melts, not even in the summer, and often the only land that can be cultivated is on high plateaus where the inhabitants can often look down on the clouds. There is no warm current like the gulf stream, therefore the warmest areas (those at 60 degrees north and 60 degrees south) have a climate which, at its best, would be much like the mountains, (not the populated lowland coasts) of Scandinavia.