Plants as the climate saviors? That's right! Greening our roofs and facades definitely helps our climate. It binds CO2 and particulate matter, increases humidity, and contributes to lowering temperatures during hot summers. Cooler air (less hot air) means less air movement, means less whirled up dust and dirt... in short, greater conditions for life to flourish! Climbing plants, particularly those with full-face greening, are so important- especially for the micro-climate.
Climbing plants bind CO2 and form carbohydrates (sugar-- leaf fibers and wood pulp). But ultimately, the amount is quite minimal (seen in autumn leaves, the increase in stem/trunk thickness, and possibly the fruit). Only the dry mass is measured in kilograms; that means that per house wall, per year-- about 2-3 car tank fillings worth of CO2 will have been absorbed by the plants from the air.
A chemical by-product of the decomposition of CO2 and the binding of carbon (C) is the release of oxygen (O2), which spreads into the ambient air via the stomata on the undersides of the leaves.
When the sun's rays reach the dark green leaves, they are partly transformed into heat. But since the chemical process of binding the CO2 needs consistently low temperatures, the heat must somehow be dissipated: water then constantly evaporates from the leaves to keep the temperature stable, which helps humidify the air. The water collected by the roots, in turn, helps in drying out facades and foundations.
Green facades will "eat" unwanted heat in the summer and provide you with air and wall cooling benefits. How is this possible? One, it is the previously described evaporation process which consumes the (heat-) energy; two, it is the chemical processes around the carbon. The heat created during combustion of carbon to carbon dioxide is needed more or less again when captured and consumed, if the carbon is again involved in photosynthesis... So the surrounding air cools and 'descends,' similar to a forest with the palpable coolness one feels. But what is even more important is that the emergence of strongly heated air is slowed down and air velocities in the ground reduced. There will be less dust whirled up, which will then limit smog formation. This topic is now even the content of scientific study!
Leaves in the garden facade also absorb dust, especially most toxic particulate matter. Once "captured," these extremely small nano-particles are hardly dangerous and are then washed away with the next rain, or are composted during autumnal leaf-fall.