Agriculture is one of the industries with the highest concentrations of outdoor workers in the US.  The Centers for Disease Control published an article today on the risks that outdoor workers may face in a warmer climate.  You can read the article here.  Among the risks are increased growth of poison ivy and other poisonous plants in a CO2-enriched atmosphere, increases in ticks and mosquitoes and their associated diseases, and increases in heat stroke and other heat-related illnesses from longer exposure to hot conditions.