The article cited in the title to this post--"Hotter Days Will Drive Global Inequality"--attempts to address the second question. According to Solomon Hsiang, a professor at the Goldman School of Public Policy at Berkeley, "labor supply, labor productivity, and crop yields all drop off dramatically between 20 °C and 30 °C." (68 °F and 86 °F). He suggests that global warming will help northern countries (i.e., northern U.S., Canada, Russia, and Europe) better off, but hurt equatorial countries.
History, common sense, and the existence of green houses tell me that Hsiang is wrong. For instance, we know from historical records that during the Medieval Warming Period, crop yields actually increased throughout Europe, including in the Mediterranean basin. Moreover, research on plants shows that Hsiang is wrong. According to this 2007 article in Plant, Cell and Environment:
In general, photosynthesis can function without harm between 0 and 30 °C in cold-adapted plants that are active in winter and early spring, or grow at high altitude and latitude (Regehr & Bazzaz 1976; Mawson, Svoboda & Cummins 1986; Larcher 2003). In plants from equitable habitats (e.g. warm season crops), photosynthesis operates safely between 7 and 40 °C, and in plants from hot environments, such as tropical species and summer species in the Mojave Desert, photosynthesis operates between 15 and 45 °C with no apparent problem (Berry & Raison 1981;Downton,Berry &Plants are categorized as either C3 or C4 depending on how they fix carbon during photosynthesis, with C3 plants generally doing better in relatively cooler temperatures, and C4 in warmer temperatures. C3 plants have an optimum temperate range of 65-75 °F, while C4 plants (which include corn) grow best at 90-95 °F. C3 plants include most small seeded cereal crops such as rice, wheat, barley, rye, and oat. C4 plants include corn or maize, sugarcane, sorghum, and millets.
Seemann 1984; Bunce 2000).
In short, Hsiang's range falls largely within the optimum temperature range for most of our cereal crops, and other important food crops (e.g., corn) actually require higher temperatures than Hsiang upper limit of productivity.
However, even if Hsiang was correct, and global warming would make northern countries better off vis-a-vis countries in warmer climes, so what? Is that wrong? No. Especially considering that, even without global warming, the northern countries are going to be better off than poorer equatorial countries.