"Future generations are going to wonder about us, the inhabitants of the Earth when the climate began to change. If seas are rising and at the same time drinking water is scarce, they are going to want to know what scientific evidence was before us and what we did in response to it. It is difficult to imagine a time in the past without an image, so I went to Montreal in 2005 to photograph the participants in the eleventh United Nations conference on climate change." Joel Sternfeld The resulting fifty-five color portraits of participants at the conference accompanied by their statements about the evidence of climate change in their home countries form the heart of this book. The mezzo busto close-ups fit within a tradition of portraiture that dates back to the Renaissance but the anxiety on their faces seems like something only modernity and the advent of ecological catastrophe could produce. A detailed, descriptive chronology of what has been termed "humanity's greatest challenge" offers readers an efficient means to grasp the scientific and governmental response to climate change, as well as its natural consequences. By the title When it Changed Sternfeld may also be referring to a much more hopeful scenario. In September 2004 the Russian federation ratified the Kyoto Protocol, and the world's first mechanism for combating carbon emissions went into effect.

At the Montreal conference the United States, one of the few non-signatories to Kyoto, worked to undermine discussions about extending the Protocol and leading newspapers predicted the end of international effort to mitigate climate change. However, when the United States delegation walked out of a late night meeting, the nations of the world joined together and agreed to take a step forward without the US or any other country that refused to appreciate the gravity of the situation. In his testimony Mohammad Reazuddin, the delegate from Bangladesh says, "My voice may be small because I am from a small country. But those who will be washed away, their voices must be heard." When it Changed represents a beginning of that process.