* BOJ must deepen understanding of climate change risks -Kuroda * Kuroda cautious about BOJ targeting green bonds in asset buying * Comments underscore BOJ’s growing focus on climate change (Recasts) TOKYO, March 5 (Reuters) - Bank of Japan Governor Haruhiko Kuroda highlighted climate change on Friday as one of the key themes in guiding monetary policy, but kept his distance from the idea of the central bank buying green bonds. The comments underscore the bank’s growing focus on climate change, a key topic of debate among central banks, some of which are stepping up purchases of green bonds used to finance clean energy and environmental projects or are considering doing so.