UNITED NATIONS — Challenged by the United Nations chief to set a new course for a warming globe and reverse the rise of heat-trapping gases, world leader after world leader Tuesday made promises of billions of dollars and better care of planet Earth.

Tuesday’s one-day summit at the annual U.N. General Assembly gathering of more than 100 world leaders is a forum for non-binding pledges. It was designed to lay the groundwork for a new global treaty to tackle climate change in December 2015.

“Today we must set the world on a new course,” United Nations Secretary-General Ban Ki-Moon said in opening remarks. “Climate change is the defining issue of our age. It is defining our present. Our response will define our future.”

And world leaders took over with the first of many of the non-binding pledges, promising by mid-morning a total of at least $5 billion to help the world become more sustainable.