Is global warming an imminent threat? why or why

Global warming, which scientists prefer to call "climate change," is definitely an imminent threat (meaning that it is a threat right now). It's also a very serious long-term threat.

The most imminent threats of climate change include flooding and severe weather patterns. As more and more pollutants fill the atmosphere, they create a greenhouse effect, meaning that they trap heat in the atmosphere. This is causing the ice caps in the Arctic and Antarctic, as well as glaciers around the world, to melt much more rapidly than usual, causing serious flooding in coastal areas around the world.

Some scientists even ague that entire countries (like the Maldives, a country made entirely of islands), could be entirely underwater within the next 50 to 100 years. 

Other imminent threats include severe weather patterns. An sharp increase in blizzards, droughts, and tornadoes have all been attributed to climate change.