Yeah, and doubling the amount of a contaminant from the natural baseline has no effect. </sarc>
Even if we're adapted to the environmental levels, that doesn't mean doubling it has no effect. Oxygen is natural and has always been in our atmosphere, too, but if you double the concentration from about 20% to 40%, you'll notice effects on humans.
Well, dufus, if you and the rest of the global warming crowd think doubling the amount of mercury introduced by man somehow equates to doubling the natural baseline we see how the whole green scam advances in your thinking.
The percentage of mercury introduced by man is as tiny a percentage as the portion of CO2 that is introduced by man.
You toddle off to your earthday planning comittee and have a nice day. Don’t cry if anyone says anything mean.