each 1 degree Celsius rise in temperature reduces overall crop yields by 10%.

That sounds on the high side, so I'd want to read a source before I accept it. Let's say it's true for a moment, and crop yields decline by 20-40% over the next 80 years. Take a look at global wheat yields over time. The use of technology to improve yields has resulted in explosive growth to output. Our continued improvements for the next 80 years will more than make up for even a 40% reduction.

I must be clear: I am well aware that there will be consequences to a 2-4C increase in temperature. I'm claiming that those consequences are not as bad as the millions of people dying each year at present because they lack access to cheap energy.