A global warming of 2.5ºC would make the average person feel as if she had lost 1.3% of her income, 1.3% being the average of the 11 estimates at 2.5ºC.Compared to what? Apparently not the costs of preventing the warming from occurring, which Tol thinks is impossible. But;
Researchers disagree on the sign of the net impact; climate change may lead to a welfare gain or loss.And in the short term, it's almost certainly a benefit.
Initial warming is positive on net, while further warming would lead to net damages. The initially positive impacts do not imply that greenhouse gas emissions should be subsidised. The incremental impacts turn negative at around 1.1ºC global warming, which cannot be avoided. The initial net benefits of climate change are sunk.
.... The uncertainty is large. The 95% confidence interval in Figure 1 may be an underestimate of the true uncertainty, as experts tend to be overconfident and also the 27 estimates were derived by a group of researchers who know each other well. Taking the confidence interval at face value, the impact of climate change does not significantly deviate from zero until 3.5°C warming.All bolds above by HSIB. Tol's conclusion:
In sum, breaking the 2ºC target is not a disaster. The most serious impacts are symptoms of poverty rather than climate change. Other impacts are unlikely to have a substantial effect on human welfare.Deal with it.