Not to shake the hornet's nest, but CO2 and other GHG are pollution.

As the capacity of natural systems to absorb industrial excesses declines, pollution will become more visible. E.g., oceanic dead zones, acidification, and coral bleaching. Then add indirect effects like increasing methane release from melting tundra.

-- Philip B. / Washington, DC

For ecosystems, as for individual life forms, there are many things that are essential but are toxic in sufficient quantity (e.g. water, oxygen). The issue is the dose. Pollution is set in the public mind as referring to stuff that has no positive value at any dose.