Wetlands act as a sponge to keep water where it fell and slow its movement to the main arterial rivers.
Habitat destruction is honestly something that concerns me much more than carbon emissions.
People also seem to forget the Red River basin (e.g., North Dakota, Minnesota, Manitoba) that flows north to Hudson Bay was a massive lake about 10,000 years ago called Lake Agassiz. So its periodic flood pattern is expected. The topography today is a flat flood plain. Because of the lake bottom history, the soil is extremely fertile. But the cities Fargo, Grand Forks, and Winnipeg are not well placed to avoid flooding. Floods happened in the early 1800s before the arrival of settlements, wetland draining, plowing, etc.
It is used on more than just wetlands, though in all cases it speeds the movement of waters to main arterial rivers.