Mayor Michael Bloomberg spent Tuesday in Rio de Janeiro for the C-40 Conference on climate change.

The conference included a roundtable discussion with mayors from around the world. They discussed environmental and legislative challenges facing their cities and countries.

Bloomberg, who is the chairman of C-40, said the group of 58 megacities has taken up nearly 5,000 initiatives to combat global warming.

The conference comes on the eve of Rio+20, the United Nations' conference on sustainable development.