In 1988, when world leaders convened their first global conference on climate change, in Toronto, the Earth’s average temperature was a bit more than half a degree Celsius above the average of the last two decades of the 19th century, according to measurements by NASA.

Global emissions of greenhouse gases amounted to the equivalent of some 30 billion tons of carbon dioxide a year — excluding those from deforestation and land use. Worried about its accumulation, the gathered scientists and policymakers called on the world to cut CO 2 emissions by a fifth.

That didn’t happen, of course. By 1997, when climate diplomats from the world’s leading nations gathered to negotiate a round of emissions cuts in Kyoto, Japan, emissions had risen to some 35 billion tons and the global surface temperature was roughly 0.7 of a degree Celsius above the average of the late 19th century.

It took almost two decades for the next breakthrough. When diplomats from virtually every country gathered in Paris just over two years ago to hash out another agreement to combat climate change, the world’s surface temperature was already about 1.1 degrees Celsius above its average at the end of the 1800s. And greenhouse gas emissions totaled just under 50 billion tons.