When international delegates arrived at Karuizawa Station for the Group of 20 environment ministers' meeting earlier this month, they were greeted by local schoolchildren, bilingual volunteers — and a wild boar the size of an elephant.

Constructed from various forms of household waste, including garbage bags, the art piece, sent from Maniwa, Okayama Prefecture, was not exactly fearsome. But the message was clear — the world needs to tackle the problem of plastic waste.

The issue, especially that of marine plastic waste, was one of the key discussions at the Karuizawa summit, and it will be again at the G20 leaders' summit, which kicks off in Osaka on Friday.