To my knowledge, there had been an understanding that scientists were being fairly conservative with their statements of how bad things were going to get, and how fast it was going to happen.
I know of two primary drivers for this (which I am somewhat oversimplifying for brevity):
Scientists really didn't want to get it wrong by saying X will definitely happen by year Y, and then be wrong, thus giving ammunition to climate deniers and vested interests running counter-PR such as oil companies.
Scientists didn't want to paint a picture of unstoppable, inevitable doom that no person could possibly imagine a way for them to fix, or contribute to fixing, thus leading to the mindset of 'if there's no way to stop it why even try?'.