Terraforming of Mars utilises Resslin Atmospheric Processors (or RAPs for short). RAPs are massive structures that resemble a large pinecone. Each of the ‘leaves’ that give the RAP its unique appearance contain a series of atmospheric scrubbers and converters that take in carbon dioxide and release oxygen. Filters work to scrub other aspects of the atmosphere until those elements have been reduced to a point that is safe for humans to breathe. Pumps deep inside drive the cleaned and scrubbed atmosphere up through a series of cables to a distribution node that flies two miles up. The process of terraforming requires decades to complete. As the atmosphere is scrubbed, basic forms of algae are introduced that help convert the atmosphere. Dozens of RAPs are positioned evenly across the surface of the world to accelerate the conversion.
Many RAP Towers have associate PFC mining units, which additionally pump these Greenhouse Gases into the upper atmosphere. The buildup of carbon dioxide and oxygen in the atmosphere will eventually trigger a greenhouse effect, raising temperatures and increases in atmospheric pressure. The melting of the permafrost will increase this trend, transforming Mars into a waterworld again.
In the depths of the Valles Marineris these changes are already starting to occur to the extent that pressure suits are no longer required. As the process advances they will not be needed at all.