There's something of an assumption among the climate-change-scoffists that mankind is far too insignificant to effect climate change. I've long thought this position both underestimates our innate troublesomeness and overestimates the climate's robustness. See, our carbon contributions don't have to effect the entire planet, just the air and water. Considering how tiny a percentage each contributes to the mass of the entire globe might make the vulnerability of the climate system a little easier to visualize.
Left: All the water in the world (1.4087 billion cubic kilometres of it) including sea water, ice, lakes, rivers, ground water, clouds, etc. Right: All the air in the atmosphere (5140 trillion tonnes of it) gathered into a ball at sea-level density. Shown on the same scale as the Earth.