The average global temperature, for night and day, is now 19 degrees. If that doesn't sound much, consider it this way: an average day on Earth is 35 per cent hotter than it was during the 20th century.
The best scientific estimates suggest that the last time it was this hot was during the Eocene, more than 30 million years ago, and long before humans turned up. Back then, temperatures rose gradually over many thousands of years. We've watched it happen in 100.