Greenhouse gases are abundant in the atmosphere, a result of waiting so long to act. Of course, we did not always realize there was a problem. Just forty years back we worried about global cooling, and new ice sheets forming. So, the change in mindset by scientists was not at first unified, and the severity of the problem was not known.
The situation is greenhouse gases do not simply go away, except water vapor which precipitates out. The removal of greenhouse gases takes time, and the one we can easily discuss as within our control is carbon dioxide. Carbon dioxide is removed by plants. It is absorbed, the carbon used for plant growth, and the oxygen returned to the atmosphere. Yes, plants will have more carbon dioxide to breath in, but there are inadequate plants to handle the removal of the excessive amounts of carbon dioxide in a short period of time. So, the atmosphere will continue to absorb energy and reemit it back to the Earth for some time, even if we stop adding to the problem.
As an analogy, consider a greenhouse. Light passes into the greenhouse, is converted to infrared rays, and emitted back. A glass panel reflects infrared like a mirror. Even if we open the windows for a day, the greenhouse will heat up the next day after the windows are again closed.