One of the most recent one is this one the Bill Gates has reportedly dropped some cash into. What they fail to talk about is with less light. what will be the impact to crop yields? How long will it take to stop the effects of shooting seawater into the air should it turn out the raining salty water on everyone is a bad idea?
The last onie is the critical one to my mind, and should be boiled down to one question that should be answered about all these efforts:
"If we realize that is a bad idea, how long would it take to stop?"
Anything that's long then a week should just be scrapped.
The solution I would like to see researched would be to put giant sheets of material in orbit. Several squares that we can send up a piece at a time and have it automatically attached to another piece. So we are building it as needed. We could also decommission it a piece at a time. Or if it become s critical mistake, do commission it from orbit immediately. Or push it closer to the sun so it has less of an effect. You could even put up a material that only blocks specific frequency of light.
Also, we should be in a global effort to plan relocation of people and crops. This will take a long time, so make a plan and be ready.