Other cities- Lae, Rabaul, Goroka, Madang. Ranges from humid tropical to alpine. Seasonal variations are slight. In the highlands, temperature varies with altitude.
Fluctuations are much greater in the highlands where temperatures are lower.
Notable exceptions are the broad lowland valleys of the Markham and Ramu Rivers and many highland valley systems, where alluvial loams or soils of volcanic origin can be very productive. The greatest soil fertility problem, leaching, results from heavy rainfall and already has degraded the soils of the Sepik and Daru Plains. The establishment of adequate transport and communication facilities is both difficult and expensive because these geographical and climatic conditions inhibit the development of some of the interior and have a negative impact upon the entire process of social, political, and economic integration and development. Malanesian Pidgin, English, Motu, and more than 700 local languages. The indigenous population of Papua New Guinea is one of the most heterogeneous in the world.