A 4°C temperature rise
An average heating of the entire globe by 4°C would render the planet unrecognisable from anything humans have ever experienced. The last time the world was this hot was 15 million years ago during the miocene, when intense volcanic eruptions in western North America emitted vast quantities of CO2. Sea levels rose some 40 metres higher than today and lush forests grew in Antarctica and the Arctic. A 4°C rise in global average temperatures would force humans away from equatorial regions. This is how the future would look according to an article in the Guardian which summarises scientific findings.
The Guardian 18 May 2019