However, the combined contribution of these sources to the increase of this gas in the atmosphere is thought to be minor. The use of nitrate and ammonium fertilizers to enhance plant growth is another source of nitrous oxide. Accurate measurements of how much nitrous oxide is being released from fertilization have been difficult to obtain. Ozone's role in the enhancement of the greenhouse effect has been difficult to determine scientifically. Concentrations of ozone gas are found in two different regions of the Earth's atmosphere.
Ozone is also highly concentrated at the Earth's surface.
Most of this ozone is created as an artificial by product of photochemical smog . In summary, the greenhouse effect causes the atmosphere to trap more heat energy at the Earth's surface and within the atmosphere by absorbing and re-emitting longwave energy. Without the greenhouse effect the Earth's average global temperature would be -18 degrees Celsius, rather than the present 15 degrees Celsius. In the last few centuries, the activities of humans have directly or indirectly caused the concentration of the major greenhouse gases to increase. Scientists predict that this increase may enhance the greenhouse effect making the planet warmer.