The climate of the earth throughout history has always
remained cold and frigid
stayed at a constant temperature
remained hot and humid
fluctuated between hot and cold periods

The correct answer to your question wouljd be fluctuated between hot and cold periods - D

Climate scientists have created elaborate models about how the climate on Earth has changed throughout the ages and throughout eons. They have come to the conclusion that we're in the middle of a possible increase of temperature due to man-amde global warming. 

Word of mouth.