At the end of the last ice age, temperatures were only 4 degrees lower, but Boston USA was buried under a mile of ice. 4 degrees higher than today, the Amazon will catch light.
If we want to keep the earth a nice place to live, we've got a very narrow temperature range. We're one degree up already and accelerating fast. Hence the reason why not only tree-huggers, but sensible people in engineering and aviation, are a bit concerned.
If this doesn't make you think, nothing will.
Earth temperature timeline