For the nearly nine years that I have been the United Nations secretary-general, I have traveled the world to the front-lines of climate change, and I have spoken repeatedly with world leaders, businesspeople and citizens about the need for an urgent global response.

Why do I care so much about this issue?

First, like any grandfather, I want my grandchildren to enjoy the beauty and bounty of a healthy planet. And like any human being, it grieves me to see that floods, droughts and fires are getting worse, that island nations will disappear and uncounted species will become extinct.