At a time when climate change is increasingly recognised as one of the most important challenges humanity will ever face, this statement may at first seem contradictory. But in reality it is not. The greenhouse effect is what keeps our planet’s temperate at a level where life can be sustained – very much like an actual greenhouse ensures that our protected plot of land is warm enough for our plants to grow during the cold winter months, the greenhouse effect ensure that our planet’s temperature is kept at an average of 59 degrees Fahrenheit or 15 degrees Celsius so that life can flourish.
While our greenhouse has a layer of glass blocking the heat from escaping, the Earth has greenhouse gases which absorb the Sun’s energy from escaping. These molecules are able to capture heat so that it stays within the Earth’s atmosphere. More specifically, the greenhouse effect heats the Earth because greenhouse gases absorb outgoing radiative energy, heating the atmosphere which then emits radiative energy with some of it going back towards the Earth[sc:1]. Greenhouse gasses include water vapour, methane, ozone, nitrous oxide, and carbon dioxide[sc:2].
Without its atmosphere and the greenhouse effect, the average temperature on the surface of the Earth would be zero degrees Fahrenheit or -18 degrees Celsius. Under these conditions, life on Earth would not be possible[sc:2][sc:comma][sc:3].
Greenhouse gases and their global warming potential
Not all greenhouse gases are the same and this also means that they have different characteristics in terms of how long they remain in the atmosphere and how much they can warm up the planet, otherwise known as their global warming potential. For example, the most abundant greenhouse gas is water vapour but the greenhouse gas most emitted by human activities is carbon dioxide[sc:3]. Similarly, carbon dioxide may be the biggest contributor to climate change among the greenhouse gases emitted from people’s activities, but it is not the most potent one; methane is. Methane traps about 21 times as much heat as carbon dioxide[sc:4].
Having said that, too many greenhouse gases can cause the temperature to increase out of control. Increasing the concentration of the gases also increases the amount of absorption and re-radiation, and thereby further warms the atmospheric layers and ultimately the Earth’s surface below[sc:1]. As the case of our neighbouring planet Venus illustrates, where there are abundant greenhouse gases, the average temperature at the surface is so high that no life can be sustained there either – the temperature on Venus’s surface is more than 855 degrees Fahrenheit or 457 degrees Celsius[sc:2].
Climate change and greenhouse effect
Our planet can naturally capture some greenhouse gases to maintain an equilibrium through various natural “sinks” which are part of the carbon cycle. This includes our forests, oceans as well as a number of other ecosystems that can absorb and capture carbon dioxide.
In this context, the fact that anthropogenic activities since the beginning of the Industrial Revolution in the 18th century have produced a 40% increase in the atmospheric concentration of carbon dioxide is worrying in terms of the long-term impacts on temperature change[sc:3].
So essentially, the problem with climate change is not the greenhouse effect itself or the presence of greenhouse gases but rather the increase of greenhouse gases due to human activities which in turn increases temperatures leading to global warming. Isn’t our planet just wonderfully complex?