Most G20 economies were missing in action with the United States, Britain and Brazil -- which is hosting this year's UN climate summit -- the only exceptions.

The Nations' climate chief calls the nations' plans “among the most important policy documents governments will produce this century.”

Many of the world's biggest polluter nations have missed a U.N. deadline to set new climate targets as efforts to curb global warming come under pressure following U.S. President Donald Trump's election.