Complex sentence: The present-day Kushiro Weetland had become a shallow bay, the temperature was 2 to 3 degrees higher (in centigrades) and the climate of the Wetland was like that of present-day Tohoku districts of Japan.
Split into simpler sentences: The present-day Kushiro Weetland had become a shallow bay, the temperature was to higher. The climate of the Wetland became like that of present-day Tohoku districts of Japan.