The most important sink for the excess C02 is th ocean. The problem is that as the oceans absorb more CO2 they become more acid and could evenually be come dead acid lakes.
Over the last 250 years, roughly coinciding with the Industrial Revolution, oceans have absorbed 503 billion tons of CO2, causing a 30 percent increase in ocean acidity. At current rates, ocean acidity is predicted to more than double by 2100.
acidification has been shown to significantly reduce the ability of reef-building corals to produce their skeletons.
Petropods, an importan link in the food chain, that may not be able to build shells in acid ocean:
So the seas rise, and the temperature gets warmer by a few degrees, no big deal right?
It doesn't seem like a global rise in temperature by 2° would have that big of an impact, but here are some of the effects:
Crop yield reduction of 5 to 15%
Risk of floods from a 3 to 10% increase in annual precipitation
A decrease of some fresh water river basins of 5 to 10%
An increase in the areas burned by wildfires of 200 to 400%(source)