Why was Western Europe on the margins of World History between about 600 to 1500?​

Without stratospheric ozone, which of the following would most likely occur? i. smog over major cities would be greatly reduced. ii. farms would produce surplus crops because of increased photosynthesis. iii. uv radiation would damage phytoplankton and reduce populations of aquatic consumers. i only ii only iii only i and ii i and iii