If you want a short answer 'Because even minor temperature variations play havoc with agricultural output. And 1.5 C isn't minor. Nor is it the limit for climate change - it's just the starting point.'
This is not a satisfying answer. Sure, temp variations affect current farms and what they currently grow, but if you assume adaptation, it’s not so straightforward.
"Adaptation" means: people moving from places that become uninhabitable (middle east, Africa, India, Latin America) to places that are inhabitable (Europe, USA, Russia, South America), while those people flee to places that become inhabitable (Alaska, Siberia). That's billions of people, trying to cross borders.
In the mean time there will be failed harvests and conflicts around the globe. Yes, we'll adapt, human kind in some form will survive, but it's pretty gloomy.
What if prevention is futile (human caused or not)? Wouldn't we be better off preparing (which seems practically possible) for the inevitable, rather than the futile exercise of burdening society with ESG, energy costs, etc
It's quite straightforward: The cost of 'adaptation' - moving global food production and populations - is astronomical; it's absurd. Just look at the impact of food logistics disruption in Ukraine.
Adaptation will require moving tens and hundreds of millions of people, and we live in a world where people were screaming bloody murder over accepting 20,000 refugees that were fleeing a civil war that we have been pouring weapons and missiles into for the past 12 years.
If you want a short answer 'Because even minor temperature variations play havoc with agricultural output. And 1.5 C isn't minor. Nor is it the limit for climate change - it's just the starting point.'