Although polar bears are white, you have brought up two very grey-area topics.
First, there's the whole question of "global warming." The phrase "global warming" is mentioned so often that it's taken by many to be an absolute fact: that the whole globe of this planet is warming up. And the implication is that unless we humans do something about it, it will continue to do so. I mean, none other than Al Gore says if we don't cut down our burning of fossil fuels and thereby stop putting all that carbon dioxide into the atmosphere, terrible things will happen. And one of those terrible things may be the extinction of the polar bears. Well, is this the truth? Is it? It all depends on who you ask and where you look. Is the warming just part of a natural cycle that is hundreds of thousands of years old? Is it tied somehow to sunspot cycles or some other natural causation? Or is it just a recent phenomenon? Hmmm? No one knows for sure. What is pretty sure is this: the early predictions of a steady rise in the earth's overall temperature have already been found to have been exaggerated. OK, so much for grey area number one.
Now to the plight of the polar bears. How may of them are there? What is their total population? Who does the counting? How reliable are the numbers? Well, it turns out that there are now somewhere between 20 to 25,000 polar bears, but nobody knows for sure. Are their numbers declining? Are they increasing? Nobody knows for sure. So much for grey area number two.
So here we sit (and you sit at your computer ready to write something intelligent): we have the first speculation that humans are making the earth heat up and then the other speculation that this is endangering the polar bears. But: there is no hard, reliable scientific data to support either view.
My suggestion to you is not to allow yourself to get trapped by a question that pretends to be self evident. It isn't. The white polar-bear controversy is afloat in a cold, grey sea where the ice may be increasing, or decreasing, or just doing its mysterious, natural and maybe cyclical old thing.
The previous posts have given a good road map for you to follow. I would probably echo their sentiments in pointing out that the increase of temperature melts the polar ice caps, home to the polar bears. Perhaps detailing statistics to this end might help, tracing the erosion of the ice caps over time, in particular the last fifty years. The second point could be to explain the implications of this trend. There are estimates to suggest that if it continues, 2050 will mark the end of the habitat for the polar bears as the ice caps will be gone. Research here and to this end might be fairly strong. Perhaps, another point to be made in the third body paragraph would be to discuss if this warming is of natural consequence of human made. This would allow the reader to understand the issue of global warming from natural and human made ends. At this point, it might be good to address the recently leaked emails suggesting that the global warming concern is overblown or created to increase scientific funding. I think that exploring these items might be able to give some structure to a very strong topic.
Three useful points u may want to consider are:
1. Imagine if you were about to embark on a trip to freezing weather wearing over 50 pounds of extra weight for protection, 20 extra pounds of clothing to keep you warm, and around 5 pounds of additional footwear to prevent a frostbite: How would u react if u realize it isn't all that cold after all?
2. What could you do if you cannot get rid of all that protection because you were BORN with it?
3. What are your limited options?
If you bring those three points into consideration, perhaps people would be able to experience how these lovely animals FEEL every day of their lives as a result of global warming.
I am by no means a global warming or polar bear expert, but there have been many articles recently on this issue. One point is that the ice caps are melting, so the polar bears' normal hunting territory is shrinking. Another point is that their camoflauge, white fur, evolved to allow them to be nearly invisible in the polar landscape, and now they will be unprotected by that camoflauge, since their backdrop is more often brown and/or green. They cannot possibly evolve quickly enough to solve this problem. If you can picture a brown bear in the polar region, this will give you a picture of the problem. The brown bear is easily visible and unprotected. A third aspect that you will have to do some more research on is the interbreeding of the polar bear with other kinds of bears. This can and does happen, since polar bears are now straying into other bears' territory. This might be a solution, but it could also be a problem because the traits that emerge from this kind of interbreeding could make for a very dangerous and scary bear, one that inhabits areas where man is settled.
This is an interesting topic, and I hope this helps you to get started. I have included a few links that might give you other ideas, too. Good luck!
Maybe the link that I have provided below can be of help. It has three ways in which it says that global warming is affecting polar bears.
First, it says that the warming is making the sea ice pull back farther and farther from the shores where the polar bears live.
Second, it says that global warming is causing there to be fewer feeding opportunities for the bears to feed.
Finally, it says that the bears' population is decreasing because of global warming.
The link lays out the ways that the retreating ice cause problems for the bears. I think it would probably help you ...
I attended a work shop on the extreme Artic and Antartic. It was very interesting about the changes that are taking place at the North and South Poles. This was not specifically about Polar Bears but did include the effects the changes were having on the wild life in those areas. This site may give you some ideas. I know I throughly enjoyed the experience.
Polar bear deaths are due to global warming and this is increasing rapidly. A new studies show that Polar Bears may face possible extinction. As soon as global warming increases, Polar Bears will have a difficult time finding food. In fact, numerous polar bears are feeling the effects of a shortage of food and are facing starvation.
There are an estimated 20,000 Polar Bears in the wild and they depend upon the arctic weather for their livelihood. Polar Bears depend upon the natural habitat of the Arctic, however global warming has contributed to the growing loss of Arctic Ice. Because the Polar Bear has not just one, but two layers of fur and can survive temperatures as cold as 50 below zero Fahrenheit. In fact, the Polar Bear is so well suited for Arctic weather, that warmer climates will cause the Polar Bear to overheat. One of the best ways to prevent the affects of global warming on polar bears is to stop (CO2) Carbon Dioxide emissions.