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. One sign of global warming is the rapid melting of permanent ice and snow in the polar regions. Follow-up investigation shows that the living space of polar animals such as polar bears is becoming more and more crowded in 1978- 1996. Since 1990s, the speed of Antarctic icebergs leaving the Antarctic continent has been accelerating, and the volume of Antarctic ice sheet has been shrinking rapidly.

Therefore, choose: d.