Because the current rise in temperatures really took off during the industrical revolution. Why not research the science before commenting? https://climate.nasa.gov/vital-signs/global-temperature/

It's also worth noting that the last time Earth had this much CO2 in the air was during the Palaeocene-Eocene Thermal Maximum, which lead to a minor mass extinction. Our civilisation and our economy are not suited to such temperatures. https://www.skepticalscience.com/co2-rising-ten-times-faster-than-petm-extinction.html