they do, they tend to be really labor intensive. One of the things our civilzation is based is the majority of people can do stuff other than growing food. If we end up needing half our population to work at growing food, forget capitalism or socialism. We are back to the material base for feudal ism.
Somebody: It's fine to say farming is hard. But the fact is, with modern technology, farming is less hard than it used to be. How do we know this? Because food consumes a smaller percentage of people's incomes than it used to. This is why the Occupy movement and other recent left-wing movements in the U.S. focuses upon concerns like college tuition, underwater mortgages, and health care rather than bread as socialist movements did in the past.
To the extent that agriculture comes under pressure due to climate change, this will be expressed as increases in food prices. That's a major issue certainly, but in practical terms it means we'll be spending a greater percentage of our income than we otherwise would on food, and maybe less on consumer goods, travel, homes, and entertainment. It's a constraint on growth in living standards, but not exactly the apocalypse. The problem I have with global warming alarmism is that it underestimates the real-life day-to-day apocalypse of, for example, 24,000 children dying from preventable causes everyday - not in 2100 or 2200 - but today. Strangely, people on the left concerned about global climate change seem to take it as a given that we'll have nations with Sub-Saharan levels of poverty in a century from now. If we really think that's the case, then global poverty is the issue that should be prioritized here over climate.
Anyway, saying we haven't tested agriculture in greenhouse conditions is somewhat innacurate. On a global scale that's true, but it's not as if the typical country or region is going to be experiencing unprecedented average temperatures. Imagine if someone said - Spain could have a climate like Iran in a hundred years, in terms of higher average temperatures and lower precipitation. That would be bad, but then, Iran is a country with a much bigger population than Spain today while being close to 100% self-sufficient in agriculture. Then we consider the fact that we're talking 100 years from now in a much more productive and technologically advanced world. Future generations will appreciate our concern, but frankly, they'll be more troubled by the fact we diverted resources from preserving our own miserably short lives, especially but not only in the developing world, than in investing in protecting theirs.