You are given a science question (hard-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Many scientists think that burning fossil fuels has increased the amount of carbon dioxide in the atmosphere. What effect would the increase of carbon dioxide most likely have on the planet?
(A) a cooler climate (B) a warmer climate (C) lower relative humidity (D) more ozone in the atmosphere
B