Why are they important? 
They are at the top of the eco system. If the Polar Bear becomes extinct it can lead to extinction of other animals. The Polar Bear feed’s on seal, dear and fish.  If the Polar Bear becomes extinct the numbers of these animals will dramatically increase as there main predator is no longer a threat. This would then lead to the downfall in the numbers of animals which the seal, deer and fish feed on leading to a big change in the food chain and the exaction of more animals
How do we know their numbers are falling?
Aerial surveys of Polar Bears help give a quick and cheaper way of counting the population of Polar Bears than traditional methods. It also gives a more accurate observation as it can be done quickly reducing the risk of counting bears twice. Also, some Polar Bears have tracking devices to determine their location, breading and hunting patterns and to measure distance travelled. 
Reducing global warming would go a long way to stop the Polar Ice caps from melting therefore stop the reduction in numbers of Polar Bears . This means burning less fossil fuels; oil, coal and gas therefore producing less carbon dioxide. We can use solar power, wind power, hydroelectric power and other alternative cleaner sources of power instead of fossil fuels which will not contribute to global warming. We can also stop deforestation. Trees convert carbon dioxide into glucose during photosynthesis but when a tree is cut down and burnt the carbon dioxide is released increasing the carbon dioxide concentration in the atmosphere . This means more carbon dioxide is released and less is stored.
Also, to stop the extinction of Polar Bears we could bread them to ensure stable numbers. The implication of this are that Polar Bears are wild animals so they shouldn’t be kept in small places and it would cost a lot to replicate their natural environment. This would make it very hard to breed them. Also, they are such large strong animals and they live in such harsh conditions for humans it would be hard to catch the animals to breed them as it would be very hard to catch them and transport them. Also, they are such large animals it takes years afford them to reproduce making breading them a long and costly process. However, it is possible to transport the animals, they would have to be kept in steel cages, drugged during transportation and flown to the area they would breed and be monitored in. This could increase the numbers and also give more information into other causes of why they are endangered.
[fig 2] http://www.arctic.noaa.gov/images/polarbear/schliebe_03.gif
Evaluation: I think this is a reliable piece of data as it comes from a government source which wouldn’t display false data, and investigate the legitimacy of data before displaying it.
[fig 3] http://nsidc.org/arcticseaicenews/
Evaluation: I believe this is a reliable source as it specialised in polar bear’s. it contains a lot of polar bear data and information.
Evaluation: I think this a reliable source as it contains a lot of data and research. The amount of data they supply shows they are reliable and the data is valid.
Evaluation: The purpose of this website is to inform and educate about Polar Bears so people know the effect global warming is having. It is a well known website and charity for animals. It conducts research about many different animals by experts. This makes them a reliable and valid source.
Earths temperature change from 1845 to 2005
[fig 2] the amount of sea-ice over 30 years. All finding follow the same negative correlation. Reliable as all findings are similar.
[fig 3] shows monthly decrease in polar ice. I think it is reliable as it is from the national sea and ice data centre, its purpose it to record sea and ice data and the website specialises in ice data so it should be reliable.