But what about the predictions that rising temperatures will be good for countries like Russia and increase their agricultural output? Unfortunately global warming doesn't just mean more winter bbq's it also means more extreme heat with more frequent and more severe heat waves and in some places more drought. This isn't a future prediction, it's already being observed, as the IPCC found:
"Since 1950, the number of heat waves has increased........The extent of regions affected by droughts has also increased as precipitation over land has marginally decreased while evaporation has increased due to warmer conditions".So what about Russia? Large parts of western Russia are currently in the grips of an unprecedented two month long heat wave that has shattered temperature records. The death rate in Moscow has soared. The record heat combined with drought has lead to thousands of wildfires breaking out with loss of life, villages and air thick with smog. Heat and drought has also lead to the loss of millions of acres of wheat (leading a ban on wheat exports for the rest of the year and spike in world prices).
So yes, while in some years Russia may benefit from longer growing seasons it will also have more years like 2010 (currently the hottest year on record worldwide) with extreme heat and heatwaves, which if anything like this year, won't be good at all. And of course it's worth mentioning that global warming has only really just begun, currently temperatures are up ~0.65 dC and our most optimistic proposals are generally to attempt to hold warming below 2 dC, better get to work.