Instead of going for global warming choose an easy topic such as Enviornment .you can start with like ‘what would happen if our environment was filled with pollution and dirt? would we be able to live in this type of environment ?No strictly a No only imagining about that type of environment is very horrifying' and then add on something from yourself!! hope it helps !!
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Environment means the thing by which we are surrounded.environment includes lithosphere,atmosphere,hydrosphere which are combined together and commonly known as biosphere. 
many things are happening around us and in the world which can damage our of the problem is global warming means rise in the temperature of the earth and its surface.main cause of global warming are human for our comfort we cut trees which leads to deforestation absorb carbon dioxide from the air.carbon dioxide plays a vital role in global warming.

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