1 . On September 7, 1991, the costliest hailstorm (雹暴) in Canadian history hit Calgary’s southern suburbs. As a result, since 1996 a group of insurance companies have spent about $2 million per year on the Alberta Hail Suppression Project. Airplanes seed threatening storm cells with a chemical to make small ice crystals fall as rain before they can grow into dangerous hailstones. But farmers in east-central Alberta — downwind of the hail project flights — worry that precious moisture (水分) is being stolen from their thirsty land by the cloud seeding.

Norman Stienwand, who farms in that area, has been addressing public meetings on this issue for years. “Basically, the provincial government is letting the insurance companies protect the Calgary-Edmonton urban area from hail,” Mr. Stienwand says, “but they’re increasing drought risk as far east as Saskatchewan.”

The Alberta hail project is managed by Terry Krauss, a cloud physicist who works for Weather Modification Inc. of Fargo, North Dakota. “We affect only a very small percentage of the total moisture in the air, so we cannot be causing drought.” Dr. Krauss says. “In fact, we may be helping increase the moisture downwind by creating wetter ground.”

One doubter about the safety of cloud seeding is Chuck Doswell, a research scientist who just retired from the University of Oklahoma. “In 1999, I personally saw significant tornadoes form from a seeded storm cell in Kansas,” Dr. Doswell says. “Does cloud seeding create killer storms or reduce moisture downwind? No one really knows, of course, but the seeding goes on.”

Given the degree of doubt, Mr. Stienwand suggests, “It would be wise to stop cloud seeding.” In practice, doubt has had the opposite effect. Due to the lack of scientific proof concerning their impacts, no one has succeeded in winning a lawsuit against cloud-seeding companies. Hence, private climate engineering can proceed in relative legal safety.

2 . After years of heated debate, gray wolves were reintroduced to Yellowstone National Park. Fourteen wolves were caught in Canada and transported to the park. By last year, the Yellowstone wolf population had grown to more than 170 wolves.

Gray wolves once were seen here and there in the Yellowstone area and much of the continental United States, but they were gradually displaced by human development. By the 1920s, wolves had practically disappeared from the Yellowstone area. They went farther north into the deep forests of Canada, where there were fewer humans around.

The disappearance of the wolves had many unexpected results. Deer and elk populations — major food sources (来源) for the wolf — grew rapidly. These animals consumed large amounts of vegetation (植被), which reduced plant diversity in the park. In the absence of wolves, coyote populations also grew quickly. The coyotes killed a large percentage of the park’s red foxes, and completely drove away the park’s beavers.

As early as 1966, biologists asked the government to consider reintroducing wolves to Yellowstone Park. They hoped that wolves would be able to control the elk and coyote problems. Many farmers opposed the plan because they feared that wolves would kill their farm animals or pets.

The government spent nearly 30 years coming up with a plan to reintroduce the wolvers. The U.S. Fish and Wildlife Service carefully monitors and manages the wolf packs in Yellowstone. Today, the debate continues over how well the gray wolf is fitting in at Yellowstone. Elk, deer, and coyote populations are down, while beavers and red foxes have made a comeback. The Yellowstone wolf project has been a valuable experiment to help biologists decide whether to reintroduce wolves to other parts of the country as well.

5 . Using too much water or throwing rubbish into our rivers are clear ways that humans can put our water supply in danger, but we also affect our water supply in less obvious ways. You may wonder how paving(铺砌) a road can lead to less usable fresh water. A major part of the water we use every day is groundwater. Groundwater does not come from lakes or rivers. It comes from underground. The more roads and parking lots we pave, the less water can flow into the ground to become groundwater.

Human activity is not responsible for all water shortages(缺乏). Drier climates are of course more likely to have droughts(干旱) than areas with more rainfall, but in any case, good management can help to make sure there is enough water to meet our basic needs .

Thinking about the way we use water every day can make a big difference, too. In the United States, a family of four can use 1.5 tons of water a day! This shows how much we depend on water to live, but there’s a lot we can do to lower the number.

You can take steps to save water in your home. To start with, use the same glass for your drinking water all day. Wash it only once a day. Run your dishwasher only when it is full. Help your parents fix any leaks(滴水) in your home. You can even help to keep our water supply clean by recycling batteries instead of throwing them away.

9 . Let's take a minute to think about the water we use. The human body is 60% water and we need to drink lots of water to be healthy. When we are thirsty we just go to the kitchen and fill a glass with clean water.

    1    For example, farmers, who produce the food we eat, use water to make the plants grow. When we turn on a light or switch on a TV or a computer we use energy and we need water to produce this energy.

The truth is that we are lucky enough to have clean water whenever we want，but this is not the case for many people around the world.    2    That's around one in 10 people in the world. If we drink dirty water，we can catch diseases from the bacteria and become ill. Every year over 500，000 children die from diarrhea(腹泻)from dirty water. That's around 1，400 children every day！Also，in some countries children walk many kilometres every day to get water.    3    Therefore，they don't have time to learn how to read or write and don't get an education.

    4    On this day every year，countries around the world hold events to educate people about the problems of dirty water and that clean water is something that everyone should have around the world. At one school in the UK，children between the ages of 10 and 15 walk 6km with six litres of water.    5    People give them money to do this and all the money helps get clean water to as many people as possible around the world.

10 . Milwaukee, Wisconsin, is road testing a new way to keep winter roads ice-free – by spreading on them cheese brine, the salty liquid used to make soft cheese, like mozzarella.

Wisconsin, also called "America's Dairyland," is famous for its cheese. The state produced 2.8 billion pounds of cheese last year! As a result, there was a lot of leftover cheese brine. Disposing of(处置)the brine can be expensive. So what should cheese makers do with the waste?

Normally, towns use rock salt to de-ice streets. The salt lowers waters' freezing point, causing ice to melt(融化). But using cheese brine could help both cheese producers and cities save money, while keeping roads safe. Cheese brine has salt in it, which, like the rock salt, helps lower water's freezing point.

In addition to saving money, cheese brine could also be a more environment-friendly option. Many people suspect that all the rock salt used every winter is harming the environment.

Rock salt is made of sodium chloride, the sane con-pound (化合物)in ordinary table salt. Sounds harmless, right? But while you probably add only a small amount of salt to your food, road crews spread about 20 million tons of salt on U.S. Roads every year!

The chemical washes off roads and goes into the ground. There it can pollute drinking water, harm plants. and eat away soil. By spreading cheese brine on streets before adding a layer of rock salt, Milwaukee may be able to cut its rock salt use by 30 percent.

Cheese brine has a downside too – a shell similar to that of bad milk. "I don't really mind it," Emil Norby told Modern Farmer magazine. He works for one of Wisconsin's county highway commissions and came up with the idea of using cheese brine. "Our roads smell like Wisconsin!" he said.