A natural phenomenon that becomes harmful due to carbon emissions is

The greenhouse effect is a natural warming of the planet by heat-trapping gases, but rising carbon emissions strengthen it into a harmful, excess warming.

Global warming is the outcome of the intensified effect rather than the underlying natural phenomenon itself.

Ecological balance is the stable interplay of organisms and environment, not a process turned harmful by carbon.

Desertification is land degradation into desert and is a consequence of climate change, not the natural phenomenon in question.

Without any natural greenhouse effect the Earth would be far colder and largely frozen.

Extra carbon dioxide and methane are the main forces amplifying it today.