> People apparently survived during the Ice Age, which was quite a bit colder than 4 deg, so I'm guessing the +4 deg is handleable, too. As far as I'm concerne

> People apparently survived during the Ice Age, which was quite a bit colder than 4 deg, so I'm guessing the +4 deg is handleable, too. As far as I'm concerned, the point isn't about what temperature is objectively best, it's about the degree of change, and the cost of adaptation. Modern industrial civilization is built up progressively in certain geographical locations, with absolutely enormous sunk investments. If we had built our cities, our towns, our power plants, and ports during a climactic equivalent to the last ice-age, we would be absolutely fucked if the climate shifted in a short period of time to where it is now. During the last ice age there was a land mass which linked Britain to Norway, Denmark, France and the Netherlands, and sea levels were 100m lower than they are today. The northern ice cap covered everything north of London, and the Sahara was fertile. To go from that climate to the climate today would involve a level of cost that it is difficult to comprehend.