Arth has generally a warm, wet climate, dictated by its large oceans. It has no polar ice caps, and the polar seas act as a source of cold storms that bring colder weather and heavy rainfall to the northern and southern ranges of the temperate zones. The tropical zone is broad, and are characterised by soaring temperatures and fierce, but short-lived storms that typically punish the coastal regions. However, one consequence of the moderating influence of the oceans is that the interior of both continents gets much less rain, giving rise to the broad, semi-arid grasslands that constitute the bulk of the centre of both Lumulea and and Gorgamelle.
The map below shows typical daytime temperatures during summer and winter on Arth. These are of course broad generalisations - local conditions can cause great variation, and the weather itself can vary wildly. In general, however, it is fair to say that the climate of Arth is both warmer and more moderate than that of our own world - and the tropics tend to be significantly hotter than those of our world.