Between a quarter and one third of all marine species rely on coral reefs (珊瑚礁)at some point in their life cycle. The Great Barrier Reef, the world's largest coral reef, covers nearly 133,000 square miles and is home to more than 1,500 species of fish, 411 species of hard coral and dozens of other species.

Australian's Great Barrier Reef has lost 50% of its coral populations in the last three decades, with climate change a key driver of reef disturbance, a new study has found.

Researchers from the Centre of Excellence for Coral Reef Studies, in Queensland, northeastern Australia, studied coral communities and their colony size along the length of the Great Barrier Reef between 1995 and 2017, finding reduction of virtually all coral populations.

“We found the number of small, medium and large coral on the Great Barrier Reef has dropped by more than 50% since the 1990s," reported co-author Terry Hughes, a professor at the centre, in a statement.

Reefs are basic to the health of marine ecosystems — without them, ecosystems collapse, and marine life dies. Coral population sizes are also considered important when it comes to the coral's ability to reproduce." A coral population has millions of small, baby corals, as well as many large ones,“ said Andy Dietzel, a doctoral student in a statement. "Our results show the ability of the Great Barrier Reef to recover becomes weak compared to the past," he added.

Population falls occurred in both shallow and deep water coral species, experts found, but branching coral and table-shaped coral — which provide habitats for fish — were worst affected by mass bleaching （白化）events in 2016 and 2017, caused by record-breaking temperatures.

Warm ocean temperatures are the main driver of coral bleaching, when coral turns white as a stress response to water that is too warm. Bleaching doesn't kill coral immediately, but if temperatures remain high, eventually the coral will die, destroying a natural habitat for many species of marine life.

The new study found the serious worsening of coral colonies in the Northern and Central Great Barrier Reef following the mass bleaching events in the past five years, and experts said the southern part of the reef also suffered record-breaking temperatures in early 2020.

“We used to think the Great Barrier Reef is protected by its huge size — but our results show that even the world's largest and relatively well-protected reef system is increasingly dropping, Hughes said. He warned that climate change is driving an increase in the frequency of the reef disturbance like marine heat waves. "There is no time to lose — we must sharply reduce greenhouse gases as soon as possible," he said.

“What kind of rubbish are you?” This question might normally cause anger, but in Shanghai it has brought about complaints(抱怨) over the past month. On July 1^st, 2019, the city introduced strict trash-sorting rules that are expected to be used as a model for the country. Residents must divide their waste into four separate groups and throw it into specific public bins.

Shanghai is faced with an obvious environmental problem. It produces 9 million tons of rubbish a year, and the number is rising quickly. Like other cities in China, it is in short of a recycling system. Instead, it has relied on trash pickers to pick out whatever can be reused. This has limitations. As people get wealthier, fewer of them want to do such dirty work. The waste, meanwhile, just keeps piling up.

Many people appear to be bothered by the details. Rubbish must be divided according to whether it is food, recyclable, dry or hazardous(有害的), the differences among which can be complex and confusing. Some have complained that they must put food waste straight in the required public bin, forcing them to tear open plastic bags and throw it by hand. Most annoying are the short scheduled time for throwing trash, typically a couple of hours, morning and evening. This means that people go at around the same time and anyone can keep an eye on what is being thrown out; no one wants to look bad.

People who fail to obey the rules will be punished. They could be hit with fines of up to 200 yuan ($29). For repeat violators, the city can add black marks to their credit records, making it harder for them to get bank loans or even buy train tickets.

However, others support the idea of recycling in general and say a tough campaign is necessary. “Slowly people will get used to it,” says Li Changjun of Fudan University.

Each year, millions of visitors crowd into many national parks. With their unmatched beauty, the national parks offer people a place to go to restore their energy. The parks we enjoy today, however, might not be around without the past efforts of a few people who supported an idea to protect the natural beauty of our country.

One of these people was the naturalist John Muir. In 1867, on his way west to San Francisco, John Muir walked through Yosemite and quickly recognized its incomparable beauty. Muir devoted himself to learning as much about the wilderness as he could. Then, he would pass this learning on to others in the many articles he wrote describing the beauty of the area. In order to protect Yosemite from damage, Muir became the voice behind a government bill that would create Yosemite National Park. Soon other bills would follow, and Muir would continue his fight to make Americans understand the importance of protecting the wild. In 1901, Muir wrote a book about the national parks, which caught the attention of people all over the United States, including President Theodore Roosevelt.

At a young age,Theodore Roosevelt had shown signs of a passion that would strengthen throughout his lifetime. During a trip to North Dakota in 1883 he saw the damage done to the land and its wildlife.

Roosevelt would take his ideas about conservation with him to the White House as the country's 26th president. He would go on to create the U. S. Forest Service, 150 national forests, and 5 national parks. Roosevelt even canceled a 1903 presidential speaking tour in order to spend two weeks camping in Yellowstone, where he gave a speech calling for its protection. While visiting Yosemite, Roosevelt camped for three days with John Muir, who showed the president around and persuaded him to make Yosemite Valley a part of the larger Yosemite National Park. After the trip, Roosevelt commented that there was no better person in the world with whom to see and appreciate Yosemite.

The natural beauty that tourists from around the world enjoy today in the country's national parks is largely due to the efforts of Roosevelt and Muir, who devoted themselves to an idea that has benefited all people.