An argument is a series of statements or propositions that support an overall conclusion. If your topic is the human impact on global warming and climate change, you will gather those statements that support your position on the matter, whether in support of or against. If you are making the case that human activity contributes to global warming, this will be your conclusion. All your statements should support your conclusion.
Supporting your conclusion are premises. These are statements, or reasons, that explicitly state supporting facts for your conclusion. In the case of human activity contributing to climate change, you might select such premises as statistics that demonstrate an increase in carbon dioxide in the atmosphere following the Industrial Revolution, as well as how deforestation gets rid of the trees that absorb these higher levels of carbon dioxide. If you select an oppositional statement as your premise, follow it with a statement that indicates why the statement may be false.
Your premises are statements commonly indicated by words like "therefore," "because," "given that" and "for this reason." In your argument that human activity contributes to global warming, you might construct a premise by saying, "The amount of carbon dioxide in the atmosphere has nearly doubled since the Industrial Revolution, therefore it is likely that burning fossil fuels has exacerbated the greenhouse effect that contributes to global warming."
Because your premises support your conclusion, your conclusion is only as strong as its supporting evidence. This will validate your point with facts and statistics, and you may use as many or as few as you feel need be made to serve your point. In the case of global warming, select scientific statistics from reputable sources, such as the National Oceanic and Atmospheric Administration, as part of your premises for your argument. This helps you present a strong argument that can be more effective as a persuasive communications tool.