The greenhouse effect is the natural warming of the Earth’s atmosphere. Solar radiation enters the atmosphere mainly as light, and some of that radiation is absorbed by the Earth’s surface then changed to heat that is re-radiated into the atmosphere where it is absorbed by greenhouse gases then re-radiated back to Earth again.
How does warming of the Earth’s atmosphere occur?
The greenhouse effect occurs naturally, and without it, the Earth would be -19ºC on average.
Total solar radiation entering the atmosphere is 342 Watts per square metre (W/m-2). This is mainly visible light (short wave radiation) but also some ultra-violet radiation and infra-red radiation (heat or long wave radiation).
Of the incoming solar radiation
- 31% is reflected back to space by clouds, aerosols, the Earth’s surface and atmosphere
- about 20% is absorbed by the atmosphere
- 49% is absorbed by the Earth’s surface then transformed to infra-red radiation (heat) and re-radiated into the atmosphere
Some heat is lost to space, while the rest is absorbed by greenhouse gases, warming the Earth’s atmosphere to an average 14ºC.
Which are the greenhouse gases?
The main greenhouse gases are:
- water vapour (H20)
- carbon dioxide (CO2)
- methane (CH4)
- nitrous oxide (N2O)
- ozone (O3)
- fluorocarbons
- chlorofluorocarbons
- sulfur hexafluoride (SF6)
What makes them greenhouse gases?
These gas molecules, in particular, are all bound loosely enough to absorb heat. Once heat is absorbed, the molecule vibrates and heat is released and absorbed by another molecule.
Do all greenhouse gases have the same effect?
Each gas differs in its effectiveness at absorbing heat, the effect it has on other greenhouse gases, and the average time it stays in the atmosphere and consequently its potential for warming over time.
Reflection of solar radiation by clouds
The greenhouse effect is the natural warming of the Earth’s atmosphere. Solar radiation enters the atmosphere mainly as light, and some of that radiation is absorbed by the Earth’s surface then changed to heat that is reradiated into the atmosphere where it is absorbed by greenhouse gases then reradiated back to Earth again.
Of the incoming solar radiation, 31% is reflected back to space by clouds, aerosols, the Earth’s surface and atmosphere, about 20% is absorbed by the atmosphere and 49% is absorbed by the Earth’s surface then transformed to infra-red radiation (heat) and re-radiated into the atmosphere.
Methane, for instance, is considered to be 28 times more effective at warming than carbon dioxide over 100 years! Although methane lasts about 10-12 years in the atmosphere, whereas carbon dioxide lasts for 50–200 years, methane indirectly affects ozone and water vapour, making it a more effective greenhouse gas. Methane comes from many sources – in New Zealand, our many cows and sheep are responsible for high methane production.
The table below shows the global warming potential (GWP) of some greenhouse gases. (The values are from the IPCC Report, 2014).
| Table 1. Global warming potential (GWP) for greenhouse gases over 100 years | |
|---|---|
| Gas | GWP |
| Carbon dioxide (CO2) | 1 |
| Methane (CH4) | 28 |
| Nitrous oxide (N20) | 265 |
| Hydroflurocarbons | 4-12,400 |
| Sulfur hexafluoride (SF6) | 23,500 |
Changes in atmospheric gas composition
Earth’s atmospheric composition has changed throughout its existence. Initially, there was very little oxygen and the atmosphere consisted mainly of carbon dioxide and nitrogen with a little methane, ammonia and sulfur gas. When blue-green algae evolved several billion years ago, they used sunlight, carbon dioxide and water to produce carbohydrates and released oxygen as a byproduct (i.e. photosynthesis). Slowly the atmosphere accumulated enough oxygen for oxygen-breathing organisms to survive.
Today, Earth’s atmosphere is composed of:
- 78% nitrogen
- 21% oxygen
- 0.9% argon
- 0.04% carbon dioxide
- neon, helium, methane, krypton and hydrogen in smaller proportions
- water vapour in varying amounts
What evidence is there that greenhouse gases affect the Earth’s temperature?
It has been learned from ice core data from Antarctica and Greenland that, over the past 400,000 years at least, temperatures were warmer when there were more greenhouse gases in the atmosphere, and vice-versa.
Is global warming the same as the greenhouse effect?
The Earth goes through natural cycles of temperature increase and decrease due to changes in the Earth’s orbit called Milankovitch cycles. However, since 1880, the increase in global temperature by a little more than 1°C is considered by the Intergovernmental Panel on Climate Change (IPCC) to result mainly from increased greenhouse gas concentrations. From 1750 to 2019, there was an increase of 45% carbon dioxide, 150% methane and 15% nitrous oxide concentration in the atmosphere. This is due to an increase in the burning of fossil fuel, change in land use and agriculture, and decrease of carbon sinks such as forests through deforestation.
Related content
Climate change resources – planning pathways provides pedagogical advice and curriculum links to help educators with their planning. It includes an interactive that groups Hubs resources according to key teaching topics. The article Thin Ice in the classroom introduces the film Thin Ice – The Inside Story of Climate Science, which looks at our planet’s changing climate, and suggests a range of Science Learning Hub resources designed to support its use in the classroom.
Climate change – a wicked problem for classroom inquiry provides pedagogical suggestions on ways to approach this issue in ways that help to avoid overwhelming students.
See our climate change collection – full of annotated resources to unpack the science of climate change and associated socio-scientific issues.
Antarctica tipping points looks at the irreversible changes we could be facing if we fail to keep global warming below 2℃.
Activity ideas
Greenhouse simulation – use a plastic soda bottle to make and test the temperature of a bottle ‘greenhouse’ and demonstrate how light energy is transformed into heat energy.
Climate change – challenging conversations uses concept cartoons designed to to support student discussions with whānau and/or others.
Useful links
Animation explaining the greenhouse effect.
NIWA scientists are investigating climate variability which includes measurement of greenhouse gases at Baring Head near Wellington, New Zealand.
