Can small changes in atmospheric composition have any effect?

Of course lead, cadmium, arsenic and radiation isn't the same as CO2, but that doesn't mean that there's not an upward limit on all of these things in the environment. Small changes can have a large effect. A small fraction more democratic votes in Florida would have kept George W. Bush in Texas. A few less gallons of water and the Titanic would have stayed afloat. Basically it's not the amount, but the effect. Currently our paper thin atmosphere contains 386ppm of CO2 and rising at the rate of 12 to 15ppm per decade. Science tells us that at 350ppm, a point ped in 1990 we we're on the ragged edge of significant warming. At 400ppm the 'hockey stick' is bent beyond any denial and at 450ppm you'll see a whale of a lot of people moving north. Americans crossing the border into Canada will be called 'sunbacks' and 'illegal aliens'. On the plus side, by then Sarah Palin will be back in Alaska, cool, but still clueless.