The green house gases helps in trapping the heat and increasing the temperature of the atmosphere. The green house gases help in raising the temperature by 8 degrees on an average. If the green house gases were totally missing, the temperature would have been much lower than what it is today. The winter season would be more uncomfortable as the temperature will go below 0 degrees most of the time.
Another catastrophic effect might be extinction of humans and some animals. Carbon dioxide, which is one of the most important green house gas, is also the main component of photosynthesis. Without carbon dioxide, there will no plant on this earth and we can't get food. Since the primary source of food(plants) can't survive without carbon dioxide, human race will be extinct without it.
Another important thing is global warming would not happen without the green house gases.