When I add an appositive clause explaining subject that is different in term of singular/plural , how to choose verb agreement with the subject. Should I use " these chemical reactions" or " that is the greenhouse effect" as a subject or should I avoid all along by not adding appositive clause?
Some greenhouse gases such as carbon-monoxide or water vapor are natural gases which exist in the atmosphere already. Nevertheless, when we produce too much of the greenhouse gases, they trap the solar heat rays and prevent them from escaping from the Earth's atmosphere and surface. These chemical reactions, that is the greenhouse effect, results/ result in global warming.
Does the fact that these refers to the post-positioned the greenhouse effect affect the choice of tense?