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.
Add berries for Christmas, and you have one of the most generous plants in the garden. Hollies--usually easy to care for--sometimes require a little TLC. Usually bright and green, holly leaves sometimes turn yellow, often signaling a cultural problem. Chlorosis, one of the more serious holly ailments, is often the cause of yellow leaves. Chlorosis shows itself on hollies by all-over leaf-yellowing. Leaves start to lose their deep green color and glossiness. The severity of chlorosis determines how yellow the leaves will become. Pale green coloring of leaves can last months or even a few years. Severe cases can turn leaves completely yellow and kill a holly in one season.