Chicago can (and in some areas has - along with Boston) fixed that issue with pedestrian tunnels that allow easy movement during cold weather. A similar fix is available for southern cities but I think a more reasonable approach is just tighter pedestrian alleys that prevent full sun from ever bathing the walking surface (and reduce sun exposure to buildings) along with lots and lots of trees. Trees are seriously amazing and dissipating heat from the sun.
Once you eliminate the sun you just need to make sure that wind alleys are set up to keep air moving through the city and have regular green spaces with water to help reduce air temperature. This can be done quite sustainably - Las Vegas is actually a great example of (rather) sustainable water use from a city built in the middle of a desert.
Once you eliminate the sun you just need to make sure that wind alleys are set up to keep air moving through the city and have regular green spaces with water to help reduce air temperature. This can be done quite sustainably - Las Vegas is actually a great example of (rather) sustainable water use from a city built in the middle of a desert.