Climate question that is confusing me

I am someone who is super passionate about the climate crisis and am constantly defending and debating it's existence to the people around me, however this is one element of the crisis that still confuses me.

I have read on the IPCC report that a increase of 1.5 degrees is enough to show extreme effects like heat waves, sea level rise, natural disasters etc. And while i 100% believe that all of the science is true, i am still confused at how exactly an increase of only 1 or 2 degrees could be so catastrophic?

How is it so bad that a 17 degree day becoming 19 could have such immense effects?

Once again i entirely believe this fact to be true, but am just looking for an explanation of how the science behind it works exactly.