In fact, the Yohe paper that Romm cites suggests that
additional warming of up to 2 °C, may be on the whole a net benefit to humanity, even though, like others, it seems that study doesn't fully consider the increases in adaptive capacity and secular technological change, consideration of which would reduce future damages from climate change, effectively increasing the temperature beyond which climate change would result in net
losses globally, and reduce the benefit - cost ratio for
mitigation.