Let me explain a bit more about why global warming would be a threat (assuming that it is, in fact, happening the way most scientists think it is).

As the first answer mentioned, ice caps would melt.  This would raise the sea level and have huge impacts on low-lying areas of the world.  This makes global warming a serious threat to the very existence of small countries made up mostly of atolls (like the Marshall Islands or the Maldives).

Global warming could also change climate patterns.  This might make it so that areas that are now great for growing crops will no longer be able to sustain them.

Both of these effects would be quite serious.  That is why global warming, if real, is a threat.

Scientists have said that events such as deforestation, the use of automobiles, burning of fossil fuels, etc. will intensify the greenhouse effect. The greenhouse effect occurs within the Earth's atmosphere and acts a "heat blanket". Over time, it slowly warms up the surface of the Earth causing global warming.

There are people who believe that global warming is a threat. Those who think it is a threat will argue that global warming is placing the planet in danger. Ice caps are melting, droughts and heat waves will occur, economic issues will surface, there will more hurricanes, and there will be an increase in disease.

There are also people who believe that global warming is a natural occurring event and will happen regardless of what we do.

Why is global warming not a threat?

Global warming is a gradual increase in the Earth's surface temperature (this also includes the temperature of the oceans). Some scientists believe that global warming is a natural occurring event that will happen regardless of what humans do to the environment.

If it is a threat then I do not believe it is an immediate one. Global warming occurs because of the Greenhouse Effect that traps warm air (by trapping the suns energy) around the Earth. This happens because gases are released into the air from engines, chemical plants, etc. and they combine.

Why is global warming not a threat?

I suppose you'd have to say that it depends on the person you ask.  If you are among folks who believe that global warming is not caused by man, then you would be able to probably say that it is simply a cycle of nature, there have been warm periods before and cold periods and nature has always adjusted.  Therefore the current trend of warming is just that, a trend, and will bring about adjustments in nature and is not a real threat to us as a species.

You could also take a view that humans may have even gotten us into this but thanks to our ingenuity, our resourcefulness, and the way that we generally respond with brilliance in times of real crisis, we will be able to handle anything, even if there is a significant and lasting rise in temperature.

Why is global warming not a threat?

I think that there are couple of ways to make this argument.

First,...