It’s the race for the ultimate ecological accolade. Four countries are competing to be the first of the world’s 195 nations to go entirely carbon neutral.

Iceland, New Zealand, Norway and Costa Rica have formally signed up to go zero carbon, although each faces huge challenges.

According to Achim Steiner, UNEP’s executive director, Norway’s main issue, was “emissions from oil and gas”, whereas most of New Zealand’s pollution came from agriculture. Iceland’s “central challenge” was “transport and industry, including fishing”, while Costa Rica faced the special circumstances of being a developing country.

Steiner calls it “an idea whose time has come, driven by the urgent need to address climate change and the abundant economic opportunities emerging for those willing to embrace a transition to a green economy.”