“Our study shows that human societies have caused more than 1.5 degrees of long-term global warming.”
The IPCC puts human-caused warming at 1.31 °C, measured from an 1850-1900 baseline. Ice-core CO2 records put it at 1.49 °C from before 1700, because about 0.2 °C of warming had already happened by the time the official baseline starts. On the official yardstick we cross 1.5 °C in under ten years. The target everyone negotiates around was set against a starting line that was already moved.