If anyone tries to tell you that there’s no real evidence that humans are having much effect on the atmosphere, just show them this:

The graph represents carbon dioxide levels in the atmosphere, and the red line at the end—part of which is enlarged in the upper left of the graph—respresents the increase since the industrial revolution began.  So right now, CO2 levels are the highest they’ve been in, oh, nearly half a million years.

Hat tip to WorldChanging.