President Barack Obama addresses the 2015 Sustainable Development Summit, Sunday, Sept. 27, 2015, at United Nations headquarters. 

在本句中address sth表示向XX讲话。但是貌似也可以理解成在可持续发展大会上讲话。这时，the 2015 Sustainable Development Summit 前面应该有个介词吧？

附朗文字典信息：

to make a formal speech to a large group of people 对…发表演说：

address a meeting/conference etc

He addressed an audience of 10,000 supporters. 他对一万名支持者发表了演说。