While the climate in the past saw changes on a larger scale than visible currently, it never faced them at this pace. They were changes spanning many decades.
2015 was not only the top record hot year in history of weather reports. It was also the record-breaker by the highest margin relative to any prior record-breakers, and with a good margin on top of that. And it's forming a trend with the previous years, not a one-odd.
Not only the *value* of yearly temperature is growing.
Not only the *value growth* is increasing (speed).
The *increase of value growth* is growing too (acceleration)
That means the third derivative is non-zero. We're facing a growth that is at least of order of t^3, It's definitely not something Earth has seen in the past.