When clouds fill the sky, it gets cooler on the Earth because Water vapor is a Greenhouse Gas, it absorbs incoming Infrared Radiation (IR), from the sun preventing it from reaching the Earth’s surface. While water vapor is 100,000 more absorbing of IR than CO2, CO2 also absorbs incoming IR Sun heat and blocks it out. The Moon has no atmosphere and has a day time temperature of 250 degrees Fahrenheit, with no atmosphere to protect it from the Sun’s heat like the Earth does, it gets the full force of the Sun’s radiation. If we increase the amount of CO2 in the air, it will block out more incoming Sun heat and further cool the earth. While it will also help keep in more heat the Earth emits off its surface, the Earth gives off much less heat than the Sun. The Stefan-Boltzmann Law tells us that if the absolute temperature of the Earth changes, the heat emitted will also change by the amount of temperature changed taken to its Fourth Power. If we increase CO2 enough to block out one percent more of the current Sun heat, the S-B Law tells us the heat emitted by the Earth will fall by 4%. A 2% increase in CO2 will cause a 16% drop in Earth emitted heat.
It is simple for a physicist like Dr. Romm to lie to people who don’t know Physics. So just Google The Stefan-Boltzmann Law. There are some good YOUTUBE videos on it, take the time to learn the truth.
The only way to increase the Greenhouse Effect is to increase the surface temperature of the Earth, then with more heat, the Earth will be able to give off more heat. The greater amount of heat given off will have some of it sent back at the earth by the GHGs in the atmosphere. But if there is less GHGs in the air, then less heat will be reflected back., so you have to keep the GHGs at the same amount and increase the surface temperature. However I know of no actual way of doing that.
If there are no GHGs in the air, then there will be no Greenhouse Effect because there are no GHGs to absorb outgoing heat, but too much GHGs and too much of the Sun’s heat is block out, and no GHE as well.