This 2014 statement by The American Association of the Advancement of Science is our candidate for the most terrifying statement ever on climate change. (Emphasis and spacing have been added.)
“Most projections of climate change presume that future changes — greenhouse gas emissions, temperature increases and effects such as sea level rise — will happen incrementally.
A given amount of emission will lead to a given amount of temperature increase that will lead to a given amount of smooth incremental sea rise. However, the geological record for the climate reflects instances where a relatively small change in one element of climate led to abrupt changes in the system as a whole.
In other words, pushing global temperatures past certain thresholds could trigger abrupt, unpredictable and potentially irreversible changes that have massively disruptive and large-scale impacts. At that point, even if we do not add any additional CO2 to the atmosphere, potentially unstoppable processes are set in motion.
We can think of this as sudden climate brake and steering failure where the problem and its consequences are no longer something we can control.”