The atmospheric chemistry would be upset by cutting out sunlight. It would be like a nuclear winter and could last for tens of thousands of years. These comets are 200-300km (186 miles) in diameter they are sheer monsters and could sterilise the earth if we are hit by one.
Heat stress â Another reason for rose leaves turning yellow is the rose bush is under some sort of stress. A common cause of stress is heat stress. The rose bush turns yellow and drops its foliage in an effort to cool down in the case of heat stress.
The holes in you rose leaves are most likely caused by caterpillars. If you go out at night with a flashlight you will see them, and you can pick them off and drop them in jar of water. Or you can spray your roses with an insecticide for caterpillars. You might have to spray again in 7 days to get rid of these bugs that are eating holes on your rose leaves.