The science

Energy from the sun reaches the top of earth's atmosphere as solar radiation. As the direct solar radiation enters the earth's atmosphere and travels through it, a part of this radiation is absorbed by greenhouse gases in the atmosphere and the rest travels further to reach earth's surface. the radiation absorbed by the earth's atmosphere results in heat. Upon reaching the earth's surface, a part of the direct solar radiation is absorbed by the earth's surface elements and a part is reflected back to the atmosphere by different surface elements. on the way back, a part of the reflected terrestrial radiation is again absorbed by the greenhouse gases. Finally the radiation leaves the earth's atmosphere and goes to the space. 

Over the lifetime of earth, the greenhouse gas content of the atmosphere underwent fluctuations - reduced when absorbed by the biosphere through photosynthesis and increased when released by events like volcanic eruptions. A large amount of the atmospheric CO2, a component of the greenhouse gases was absorbed by the biosphere and were converted to their components. When the past biosphere fossilized,  the carbon got trapped inside the earth's mantle, leading to reduction of greenhouse gas content of the atmosphere, which contributed to reduction of the inferno (earth). These fossilized biosphere, over time, got converted into fossil fuels (petroleum, coal etc.) and remained trapped inside the earth for millenniums.

With the growth of industries, human discovered the utility of the fossil fuels to provide vital sources of energy. The dependency of humans on fossil fuels as the vital source of energy resulted in the release of this trapped carbon in massive amounts, leading to the increase of greenhouse gas content in the earth's atmosphere. The natural greenhouse phenomenon got affected by this anthropogenic forcing, which lead to the the ongoing global warming and climate change.