Significance Do forests in cold or dry climate zones distribute more resources in roots to enhance uptake of water and nutrients, which are scarce in such climates? Despite its importance to forest ecology and global carbon cycle modeling, this question is unanswered at present. To answer this question, we compiled and analyzed a large dataset (>6,200 forests, 61 countries) and determined that the proportion of total forest biomass in roots is greater and in foliage is smaller in increasingly cold climates. Surprisingly, allocation to roots or foliage was unrelated to aridity. These findings allow, for the first time to our knowledge, biogeographically explicit mapping of global root carbon pools, which will be useful for assessing climate change impacts on forest carbon dynamics and sequestration.