The comfortable temp for biking is significantly higher than it is for walking, especially with the right gear. 40°C is definitely beyond reasonable tho. Planting trees and decreasing the amount of asphalt would go a long way to make it a better proposition more of the year. A societal expectation that you don't go or do anything when weather gets that hot could bridge the difference. Unfortunately that kind of philosophy is antithetical to capitalism's demands for productivity.