Thanks to Earth, we have fresh air to breathe, clean water to drink and warm sunshine to enjoy. But it seems that we may have taken these things for granted and not realized that our planet is getting “sick”. 【小题1】 More than 15,000 scientists around the world have written a letter to warn about environmental challenges.

Among those environmental challenges, climate change sits at the top. Global average temperatures have risen by more than 0.5℃ since 1992. 【小题2】 It means that heat waves would last around a third longer and rainstorms would be about a third more violent if we take no action. The increase in sea levels would also be much higher. Countries like Singapore and Tokyo that are at low altitudes (海拔) may be covered by the ocean in the future.

【小题3】 It’s getting harder to get fresh water. Ocean pollution has become serious. Since 1992, the human population has grown by 2 billion, while the populations of all other animals have dropped by nearly 30 percent.

Scientists say that we are experiencing the sixth mass extinction (物种大灭绝) in history. More than two-thirds of the world’s wildlife could be gone by the end of the decade if action isn’t taken soon. 【小题4】

However, we have made some progress by making the hole in the ozone (臭氧) layer smaller. That’s because we gradually stopped using chemicals that can break down ozone, a gas that protects Earth.

【小题5】