英语口语 话题是 what is the most serious problem in the world ? why do you think so?what can we do

I think the most serious problem in the world is environment,because ,as we all see,there are more and more natural disasters happening now ,many pepole in the world are suffering due to the increasing bad weather .and the earth is becoming more and more warm because of the CO2.what we can do is to limit the wasted gases emission and plant more trees ,the most important is to warn pepole that our earth is getting worse