Which gas is responsible for the green house effect and why?

Answer 1

There are multiple gasses that are responsible for the "greenhouse effect"; however, water vapor and carbon dioxide are the gasses that cause the most significant effect.

The reasons for this are rather complex. However, the layman's explanation is that the sun emits radiation to the Earth. This radiation is converted to heat energy and infrared radiation. Normally, this radiation bounces off of the Earth and exits into space. However, greenhouse gasses have the ability to absorb this radiation and re-emit them back to Earth, causing an additional source of heat. Over time, this can have a cumulative effect, causing climate shifts.