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.
yumtomatoes(10a/FLA)August 9, 2011. The leaves on my desert roses in the front of the house, which doesn't get sun until 11 am (western exposure), are turning yellow and falling off. They do get a couple of brown spots on some of them before they turn yellow. I have sprayed them with fungicide a couple of times. The plants are in pots, not in the ground.