The similarities between Noah's time and the late 20th century are that people in various societies and cultures are continuing to do what people do, without giving much regard to the signs of the times. This happened in Noah’s day, and with Lot as well, and this continued on into the late 20th century, and even today.
In Noah’s day the Bible states, “And just as it happened in the days of Noah, so it will be also in the days of the Son of Man: they were eating, they were drinking, they were marrying, they were being given in marriage, until the day that Noah entered the ark, and the flood came and destroyed them all.” (Luke 17:26-27)
Therefore, people ridiculed Noah as he spent time building the ark. They continued to live their lives, and there is nothing wrong with that, but they did not heed the warnings to change their evil ways and live a moral life, obeying God’s commands.
In addition, the Bible states that this happened with Lot as well. "It was the same as happened in the days of Lot: they were eating, they were drinking, they were buying, they were selling, they were planting, they were building; but on the day that Lot went out from Sodom it rained fire and brimstone from heaven and destroyed them all. It will be just the same on the day that the Son of Man is revealed. On that day, the one who is on the housetop and whose goods are in the house must not go down to take them out; and likewise the one who is in the field must not turn back. Remember Lot's wife. Whoever seeks to keep his life will lose it, and whoever loses his life will preserve it.” (Luke 17:28-32)
The meaning of these verses, to Christians who believe what the Bible says, is that the majority of humankind will continue on living their daily lives and not be much concerned with the fact that Jesus Christ will return as the conquering Messiah. They will be caught unawares when He returns to set up his government and headquarters in Jerusalem, just as people were caught unawares when the Flood came and when Sodom and Gomorrah were destroyed.