You may have heard of the "Butterfly Effect". It comes from ideas set out by MIT Meteorologist Edward Lorenz. In his seminal paper "Deterministic non-periodic flow" (1963), he set out a model of atmospheric convection and showed that temperature and fluid motion interact very non-linearly as one feedbacks into the other. This means a small change in one, can have little impact in the other. But doing another small change in one can cause a feedback loop which creates a huge effect in the other. In his words, "one flap of a seagull's wings would be enough to alter the course of the weather forever".
The scary conclusion this leads to is that the climate doesn't always change gradually. After decades of gradual change from temperature increases, it can hit a tipping point where a feedback loop occurs leading to very rapid change, very suddenly.
And unfortunately we don't know exactly where this will occur. Many climate scientists believe we're already there.