I really feel sorry for the people that flap their mouths repeating the stuff they hear on "Faux News" thinking that they actually gain knowledge..
There are a lot of things that "greenhouse gasses" do... the name should give you a pretty good idea of what that is. If you go into a greenhouse, the temperature is much higher than the outside temperature.. The glass roof lets in sunlight and infrared, yet tends to contain the heat that comes from that from escaping back to outside. Greenhouse gases do the same thing, acting as the "window" to space, allowing heat in, but not as much out. This raises the overall average temperature of the surface of the earth. While there are many sources of these gases, the primary gas is CO2. The burning of fossil fuels, the elimination of forests, the industrial activity all serve to raise the level of CO2, which in turn raises the average temperature of the surface of the earth. The results of this warming trend are various, and not the topic of this question.
Greenhouse gasses don't cause global warming. There are natural greenhouse gases on our earth . Carbon dioxide is one of the gasses and when there are is too much co2 created by humans it heats the earth . This heat warms the earths overall temperatures.
Supposedly they prevent heat from leaving the atmosphere. However, we don't really know, and people only theorize on why the earth is warming. Many even theorize that the temperature of the earth is cyclical and not permanently warming at all.
The simple answer is that greenhouse gasses hold the heat produced by the sun in our atmosphere longer than otherwise would occur if the greenhouse gasses were not present in the atmosphere in such high amounts. Less greenhouse gasses, less retention of heat. Obviously some heat retention is good. Life could not flourish on earth without adequate heat. Earth will continue to exist if warming continues. Life will continue to exist, up to a certain point, too. The problem is that human life may not continue to exist or, at the very least and this is happening now, the quality of human life will suffer as the heat continues to rise.
The heat of the sunlight is way too much to sustain life and the dark space is too cold. The atmosphere of the Earth creates a shelter in between so the Earth can sustain a average temperature over the crust. The gas molecules that makes the atmosphere emits the radiation from sunlight and heats up during daytime. These gases that interfere with sunlight are called Greenhouse gases. in order for Earth to keep the ideal temperature part of the energy comes with the sunlight has to be reflected back into the space otherwise it would be too hot. The atmosphere has to be in a good balance in terms of the density of Greenhouse gases in order to achieve that. If the density of Greenhouse gases become too much, the sunlight that normally reflected back by the gases and off the surface of the Earth, couldn't reach outside the atmosphere enough and more energy would get trapped within, which would increase the temperature. Which is called Global Warming.
They really dont. Scientist are trying to scare people. They are simply saying this because some places on Earth are experiencing warmer temperatures. But really our "warmer" temperatures are lower than they were in the Middle Ages. Hope this helps!! God bless :)