The need for alternative energy sources

Now the main energy sources are fossil fuels, but I think alternative energy sources are needed for the following two reasons.
First,fossil fuels are not sustainable energy sources. If we would continue to use them as we use now, someday they would be depleted.
Second, fossil fuels emit much carbon dioxide and it causes air pollution. Also air pollution causes global warming,which would cause great disasters such as desertification, see level rising, and so on.
In conclusion, we should stop global warming as soon as we can.For this reason we should stop using fossil fuels and find alternative energy sources.

Thank you very much.