地球温暖化の影響が加味されることにより、いわゆる気候の極端化が発生し、干ばつや高温などが増えたり強まったりして、生物が危険にさらされるリスクが増すと考えられている。生態系への主な影響例として、寒冷地に生息する動物（ホッキョクグマ、アザラシ）の減少などがあげられる。ホッキョクグマは、哺乳綱食肉目クマ科に分類されるクマ。
Polar bear Quiz
Choose the correct answer.
1. The polar bear is a bear native to the ( ).
a.Arctic
b.Antarctic
c.Hokkaido
2. The polar bear is a ( ) species at high risk of extinction.
a.Immortal
b.Vulnerable
c.Invulnerable
3.Zoologists believe that the projected decreases in the polar sea ice due to ( ) will reduce their population by two thirds by mid-century.
a.Acid rain
b.Air pollution
c.Global warming
4.Although the fur appears white, in fact the individual hairs are ( ).
a.Transparent
b.Translucent
c.Clear
5.Polar bears are enormous, aggressive, curious, and potentially( ) to human.
a.Dangerous
b.Safe
c.Secure
6.The polar bear is the most ( ) member of the bear family.
a.Herbivorous
b.Omnivorous
c.Carnivorous
7.Polar bears are excellent ( ).
a.Runners
b.Swimmers
c.Hunters
8.About 60% of the world’s polar bears live in ( ).
a.Canada
b.Russia
c.America
9.The bears sometimes have problems with various skin diseases with ( ).
a.Gastritis
b.Dermatitis
c.Canker sore
10.Global warming has already had an impact on polar bear population health and ( ).
a.Size
b.Life
c.Illness
Aimi Kibushi