In about the last 100,000 years, there have been 23 abrupt temperature changes in Greenland ice cores. In those moments, the temperature abruptly jumped or fell 9 to 14 degrees Fahrenheit across the planet and 25 to 35 degrees Fahrenheit in Greenland. The changes typically took decades to generations, but at their most extreme, they only took two to three years.
Counterintuitively, published consensus statements on climate change do not factor in abrupt change — an omission that seriously affects how climate policy is made. The reason is that we do not yet have the skill to model abrupt changes, even though ample robust evidence exists of the common occurrence of abrupt change in prehistory. It may seem unimaginable that these most important of all climate changes have been disregarded in climate policy, but this is the way the culture of the climate science consensus works. Policy is based upon impacts that we project to happen in the future through modeling.