Let's look at some facts:
1) Life needs to toughen up, even oxygen created an extinction event. My ancestors were smart enough incorporate oxygen using their sheer will power to use an element that will burn in an open flame and reduce iron into oxidized piles of ash.
2) Carbon dioxide does trap a type radiation. And CO2 dissolved in water creates carbonic acid just like the CO2 in club soda.
3) Other types of radiation are able to pass through the atmosphere without being trapped
If the ocean is too acidic, then add some chalk. Using a lot of chalk in geoengineering will probably not be necessary. The carbonic acid will be neutralized in the ocean's shallowest regions first since the Earth's crust has a lot of calcium carbonate, like from where the underpaid postdoc took their samples in OP's article.
To manage the Earth's temperature and prevent infrared light from heating it then get with the oil industry to make plastic. That visible light that makes it to the Earth's surface is absorbed by the ground heating the planet and then some of the original visible light energy is emitted back into space as infrared light which is trapped by the CO2 in the atmosphere. There is a fancy concept called albedo which if increased will reflect more visible light back into space before the space invading radiation destroys the planet. One option to increase albedo would be white plastic tarps created by the oil lobbyists which would be stretched across farmland. An albedo of 0.9 will reflect 90% of the visible light back into space before the energy becomes infrared radiation. The white plastic tarps will also prevent farmland from desertification by covering the soil when the ground is fallow and most vulnerable to erosion.
As a bonus the reflected light will make the area colder and denser. As warm air passes over the cool region it may be forced to rise over the coolder air. This helps to create clouds and increases the likelihood of rain which is good for farmers.
TL;DR - American baseball chalk and tarps will save the world
