D island immigrants

In the past 50 years, greenhouse gases such as carbon dioxide emitted by human beings in the process of production and life have increased sharply, leading to global temperature rise and frequent droughts and floods. The emission of chlorofluorocarbons destroys the ozone layer in the upper air, which leads to the increase of ultraviolet radiation from the ground sun, thus endangering human health. The main reason why Tuvalu became the first "environmental refugee" country in the world is that due to the increase of carbon dioxide emissions, the earth is getting warmer, the polar glaciers are melting and the sea level is rising.

Therefore, choose: B.