For many years，scientists have warned us that our planet is getting warmer.If current trends continue，animals may start to die off and life could get very difficult for everyone.The temperature is rising because humans have been releasing massive amounts of greenhouse gases into the atmosphere，which surround the planet and keep heat from escaping.One of these gases is carbon dioxide.

　　Most carbon dioxide we produce comes from the process of making and eating food，the scientists reported in Chicago.The production of meat contributes to a lot of carbon dioxide.And much of meat’s contribution comes from beef，which is responsible for releasing even more greenhouse gases into the atmosphere.

　　The process of making a hamburger，for example，requires a lot of energy.A cow has to be fed and raised，and cow’s wastes are a major source of greenhouse gases.After the cow is killed，the meat has to be processed and shipped to a consumer，which takes fuel.And most of the cow won’t even be used for meat people eat.

　　By the time a hamburger finally lands on a dinner plate，it has taken a heavy toll on the environment.It is believed that the process of making a half­pound all­beef burger adds about 19 times the weight of hamburgers in carbon dioxide.

　　The message is clear：We can greatly reduce the production of greenhouse gases by eating less beef.Other kinds of meat like pork and chicken do less harm to the environment—at least in terms of the amount of greenhouse gases released.Nathan Pelletier，a scientist at Dalhousie University in Canada，reported that if everyone in industrial countries ate chicken instead of beef，we would cut the Earth’s greenhouse gases by more than half.

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