Marco, thank you for the cancer, asthma, birth defects, mercury, dirty snow, smog, thanks.

Here is how we know humans are responsible for the rise in CO2 warming our atmosphere and acidifying the oceans.  Not all CO2 is created equal.  Naturally occurring carbon dioxide differs from that which was sequestered underground for millions of years.  CO2 picks up a radioactive isotope when it's created, but these decay, the half life of this isotope is 5,730 years.  The organic plants and animals buried for millions of years and transformed to oil gas and coal have long been depleated of this isotope.  When the air is sampled scientist can see how many carbon dioxide atoms belong to the natural cycle, and how many were thrown into the sky by human activity.  In this way we know the CO2 that has been increasing since the last years of the 1700's are all from burning fossil fuel.
Marco doesn't get it.  He also doesn't get the Cuba thing, or the immigrant thing, not ready 2 lead.