Humans emit only 3% of natural carbon dioxide emissions?

As with many talking points of those dismissive of climate science, this one starts with a kernel of truth but quickly obscures it by withholding key information. 

What is the kernel of truth?  Biological activity each year really does put around 30 times as much carbon dioxide into the air as people do.  But just what is that biological activity?  Decay.  During autumn and winter, vegetation dies and decays, releasing a lot of carbon into the air.

What this talking point hides is the fact that spring and summer exist, during which time biological activity again removes carbon dioxide from the air.  This is a seasonal effect only.  Seasonal increase is offset by seasonal decrease.  On a net basis, natural influences are pretty stable.  Decade by decade, decay is responsible for ZERO increase in CO2 levels.

Meanwhile, decade by decade, human activity is responsible for ALL the increasing CO2.

You can see both these effects in this graph, called the Keeling Curve, which shows both the natural, seasonal variation and the human-caused, long-term increase.