When Temperature Became Global

The emergence of global temperature as a trackable metric for studying climate change and for formulating climate policy

Global temperature has become one of the most consequential numbers of the twenty-first century. In measuring planetary warming, it anchors the Paris Agreement and Net Zero goals, and shapes how we imagine the future. But how did a single number come to represent something as vast and varied as Earth’s climate? In When Temperature Became Global, Sarah Dry and Mike Hulme tell the story of the scientists who transformed scattered observations into a measure of planetary change. From the 1870s onward, researchers built large-scale temperature series to test competing theories of climate change. In the 1970s, scientists working across the Iron Curtain and in both hemispheres increasingly turned to these series to distinguish human-caused warming from natural climatic variability.

Then, around 1980, two research groups—one in the UK, the other in the United States—independently produced new global temperature series. Their work helped transform global temperature from a tool for investigating climatic variability into an authoritative and trackable metric—one that would come to structure international climate policy and planning for the future. Yet the rise of global temperature was neither obvious nor inevitable. By revealing the history of how this metric acquired its scientific authority, When Temperature Became Global illuminates both the possibilities and the limits of using a single global number to frame a changing climate and our future within it.