Greenhouse Gases

The subjects of what constitutes a greenhouse gas, and what the term greenhouse effect means are reviewed. The greenhouse effect comprises two parts; the primary effect which has been in existence for thousands of years and gives Planet Earth its hospitable average temperature of c. 17 oC and the smaller secondary effect which has been in existence for only 250300 years and is caused by an increase in concentration of greenhouse gases. Much of this increase is probably due to mankind’s activities on the planet. It is the latter effect that has caused the temperature of Planet Earth to increase by c. 1 oC since the middle of the 19th century and, following the Paris 2015 COP21 convention, it is hoped the increase can be limited to 1.5 to 2.0 oC by the end of this century. The two most significant secondary greenhouse gases are CO2 and CH4, and together they contribute c. 80-85% of the secondary effect. This percentage has not changed for the last 2030 years, but the total radiative forcing which causes the increase in the planet’s temperature has increased consistently over this time window. Despite a few unexplained observations and inconsistencies, the huge majority of the world’s scientists now accept that the increase in Planet Earth’s temperature, or global warming, is real, and will have a disastrous impact on our ecosystem and environment unless everyone can adapt their lifestyles.