Name one way other than photosynthesis that carbon dioxide is removed from the ecosystem.
Oceans absorb vast amounts of carbon dioxide, providing a natural sink for CO2. When the partial pressure of CO2 at the ocean's surface is less than that in the atmosphere, CO2 will dissolve into the water to equilibrate its partial pressure. Subsequently, surface CO2 is carried by ocean currents deeper into the ocean, and the surface concentration is diluted, allowing the pumping action to continue. Also, CO2 can dissociate or combine with other elements further reducing the surface CO2 concentration.
Warm water can hold much less CO2 than colder water. This means that when deep ocean waters rise to the surface as part of normal ocean-circulation patterns, the water heats up and can release CO2, or slow the absorbtion of new CO2 into the oceans. Once dissolved into the ocean, a carbon atom will remain there on average for about 500 years.
Over half of all man-made CO2 produced since the beginning of the industrial age has been absorbed into the oceans and by plant life. About one quarter of current emmissions are entering the ocean.