A major international gathering on climate change will open in Seoul Monday for a four-day run.

The mayors of London, Sydney and Jakarta as well as dignitaries from some 80 other world cities will participate in the third gathering of the C40 representing the world’s largest cities that have pledged to tackle climate change.

Participants are expected to discuss fighting climate change and later adopt a declaration on outlining effective ways for global cities to reduce greenhouse gas emissions.

Former U.S. President Bill Clinton, the chief director of the Clinton Foundation, is scheduled to deliver a keynote speech Tuesday on the importance of tackling climate change.