We are now living in the modern society. Most of the energy we use for heating, lighting, transportation and manufacturing （制造业）comes from fossil （化石）fuels. These are carbon-based fuels from oil, coal and natural gas. When we burn these fuels we release heat which p the energy.
There are three main disadvantages to using these fuels. Firstly, they are causing climate problems because of the G Effect. When we burn fossil fuels they produce carbon dioxide which causes global warming. Secondly, when we have used up all our coal, oil and natural gas, we will have n left to burn. Thirdly, they are not very efficient. The internal combustion engine （内燃机）that we use in most cars, trucks and buses, for example, is only about 14% efficient.
Scientists are working on another fuel — hydrogen. There are a couple of advantages to using hydrogen as a fuel. Firstly, because two-thirds of the e surface is water and water is made of hydrogen and oxygen. There is an almost unlimited supply of hydrogen. Secondly, burning hydrogen does not cause global warming. Thirdly, it is much more efficient than carbon-based fuels.
Unfortunately there are problems with hydrogen at the present time：there is the problem of separating （分离）it from water c, and there is the difficulty of storing it. It can be stored under pressure but high pressure tanks are far from safe. It can also be stored as a liquid but only at extremely low temperatures. It seems likely, therefore, that there will have to be a completely new technology before hydrogen replaces fossil fuels. S these problems is an urgent （急迫的）matter. Although China, India and Australia have huge amounts of cheap coal, and there are still l oil and gas reserves（储藏量）elsewhere, the effects on the planet's climate will be bad if they are used.
