So your premise is that the atmosphere is fragile, but the hydrosphere is not. Interesting.
If we take that premise, have you not read about the air quality issues they have in China? Per your premise, that would affect us but as "developing nations", India and China are not obligated to reduce greenhouse emissions under Kyoto.
Here's an article that disputes your premise that the pollution in India and China only affects them: Hydrosphere
Here's an article citing that trees in urban areas do better due to higher concentrations of CO2 and nighttime heat, if there is a study citing the benefits of mercury on fish, I can't find it. NYC Trees
And then there's the case of the shellfish neurotoxins: Neurotoxins
Domestically, we also have this problem called the dead zone in the gulf around the Mississippi delta, this is primarily caused by nitrogen runoff from farms and residential areas. The thing is this is a really easy problem to solve with riparian buffers that are also beneficial to wildlife as crucial habitat. Besides the nitrogen, we don't know what the long term effects of other farm chemicals will be. A much bigger potential problem than CO2 which can resolve itself if the earth warms and we have more plant life to absorb it.