Our world in danger

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 considered those things natural and haven’t realized that our planet is getting “sick”. Now scientists have given us a warning.

More than 15,000 scientists around the world have written a letter to warn about environmental threats (威胁), the Washington Post reported.

Among those environmental challenges, climate change sits at the top. Global average temperatures have risen by more than 0.5℃since 1992. A half-degree temperature rise is a big deal. It means that heat waves would last around a third longer and rainstorms would be about a third more intense (猛烈的). The increase in sea levels would be much higher, according to NASA. Countries like Singapore and Tokyo that are at low altitudes (海拔) may be covered by the ocean in the future.

But this is not the only problem people are facing. 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, according to the World Wildlife Fund. The Amur leopard (远东豹), black rhino and cross river gorilla (克罗斯河大猩猩) are some of the most endangered animals.

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

This progress shows that we can make positive changes when we act decisively, the letter says.

Since January 2013, many cities in China have seen a lot of foggy days. In Beijing, only five days in January were free of smog (雾霾). What’s the difference between fog and smog?

According to scientists, fog is made up of tiny drops of water and also ice particles (颗粒) during very cold conditions. Smog is dirty air that looks like a mixture of smoke and fog, caused mainly by smoke from cars and factories in cities.

An official for the Ministry of Environmental Protection told Beijing News that PM2.5 pollution is the main problem with air pollution. PM2.5 refers to pollution with small particles 2.5 micrometers or less in diameter.

According to the Chinese Academy of Sciences, two major factors that cause PM2.5 are motor vehicles and the burning of coal.

Poor air has done harm to people’s health. Children and the elderly are more at risk. A report from Beijing Children’s Hospital shows that from January 5 to January 11, 2013, half of the patients in the hospital came for respiratory (呼吸道的) problems.

To respond to the air problem, the Chinese government and many Chinese people have started to _______________.

Beijing announced plans to use clean fuel (燃料) in cars and plant trees. It also asked citizens to set off fewer fireworks for the Spring Festival celebration. They suggested that cars with large emissions (排放) should be banned and factories should be closely watched.

Three students from No. 4 High School in Beijing wrote a report to advise how to fight the air pollution. “We hope more people will join us in making a difference. With all our efforts, the blue skies will certainly return for good,” said Shi Yucong, 15, one of the three students.