What You’ll Learn In This Module
- What are greenhouse gases?
- Which is the most common greenhouse gas?
- Which greenhouse gases are most powerful? and how long do greenhouse gases remain in the atmosphere?
- What is producing greenhouse gases?
- What factors other than greenhouse gas might change the earth’s atmosphere?
- Are we sure that its greenhouse gases that are heating the earth?
What are greenhouse gases?
Greenhouse gases are gases in the Earth’s atmosphere which trap heat and warm the planet. They cause the greenhouse effect and climate change. The major greenhouse gases are:
- Carbon dioxide (CO2)
- Methane (CH4)
- Nitrous oxide (N2O)
- Fluorinated gases (F gases)
- Water vapour
Their impact depends on the quantity in the atmosphere, how long it remains there, and how much heat it absorbs or radiates back towards the Earth.
Many greenhouse gases occur through natural processes, but human activity is increasing the amount of them in the atmosphere.
This is especially true for carbon dioxide (CO2), methane, nitrous oxide and fluorinated gases.
The amount of water vapour in the atmosphere is reasonably constant, and any increase comes back down as rain.
Which is the most common greenhouse gas?
The chart below shows the proportions of the main greenhouse gases which are released into the atmosphere globally.
Carbon Dioxide (CO2) is the most abundant greenhouse gas and the largest contributor to global warming and climate change.
It makes up about 65% of the total global greenhouse emissions.
It’s naturally occurring and is transferred between plants, soils, the atmosphere, oceans and ice in a cycle called the carbon cycle.
But the natural amount of carbon dioxide in the atmosphere is about 280 parts of CO2 per million.
By 2020, the atmospheric concentration of CO2 had increased by 48 percent compared to its level in 1750.
The concentration of carbon dioxide in the air now stands at over 400 parts per million.
This vast increase has been because of human activity, mainly the burning of fossil fuels (like coal, oil and natural gas) which releases greenhouse gases into the atmosphere.
Which greenhouse gases are most powerful? And how long do they remain in the atmosphere?
Carbon dioxide emissions remain in the atmosphere for about 200 years and during this time they cause the planet to warm up via the greenhouse effect.
Methane, another potent greenhouse gas, is 21 times more powerful in its warming effect than Carbon Dioxide. But it has a shorter atmospheric lifetime of 25 years.
Nitrous oxide is also a long-lived greenhouse gas that accumulates in the atmosphere over decades or even centuries.
Finally, fluorinated gases are only a small proportion of the total, but are very potent gases. Some of them have 23,000 times more potential to warm the atmosphere than carbon dioxide.
If we want to stop the temperatures on earth rising more – to limit global warming e.g. to an increase of 1.5 degrees centigrade relative to preindustrial times – we have to stop (net) greenhouse gas emissions.
Since greenhouse gases remain in the atmosphere for many years, it will still take many years from the point that we stop polluting for the warming of the planet to slow down.
What is producing greenhouse gases?
According to the Intergovernmental Panel on Climate change, the major source of CO2 in the atmosphere is the burning of fossil fuels such as coal, oil and gas.
The world’s people and economy are highly dependent on fossil fuels. Currently, most of our energy comes from them.
We use them to power energy generation, to heat our homes, to make things in our factories and to power our cars, trains, planes and ships so that we can travel and transport things around the world.
The chart below shows the proportions of global CO2 emissions by economic sector.
Three-quarters of global CO2 comes from energy production, industrial processes and transport, which are all based on fossil fuels.
- Electricity generation and heat include the burning of coal, which is a particularly large contributor to global greenhouse gas emissions.
- The high carbon emissions from industrial processes include manufacturing and refining, which typically use a lot of fossil fuels.
- Important human sources of nitrous oxide include the burning of fossil fuels and industrial processes.
- Transport emissions come from the use of e.g. cars, vans and heavy goods vehicles, which burn petrol and diesel.
- Aviation, particularly long-haul flights, is a vast source of emissions as carbon dioxide and other greenhouse gases come from burning aviation fuel.
- Shipping emissions are released from the fuel that’s burned in ships and boats, for example, as goods we buy are transported around the globe.
Buildings create around 6% of global CO2 emissions.
- These come from burning fossil fuels such as oil, coal and natural gas to heat homes, retail premises and public sector buildings.
- Fluorinated gases insulate well and are used as refrigerants, aerosols and extensively in e.g. pipe insulation.
One-third of global emissions result from agriculture, forestry and land use.
- These emissions come mainly from the development of agriculture to produce the food we eat.
- Methane is produced naturally through the breakdown or decay of organic material and the digestion of food by cattle and sheep.
- Human activities creating methane include fossil fuel production, industrial livestock management, rice cultivation and waste management.
- The decomposition of biodegradable waste in landfills caused by food waste also creates methane.
- Carbon is released into the atmosphere when trees are burned or decompose and when the soil is dug and worked.
- Natural sources of nitrous oxide are largely from bacteria in the soils under natural vegetation and in the ocean.
- Important human sources include nitrous oxide fertilizers, soil cultivation in agriculture and livestock manure.
Reducing carbon emissions is an enormous challenge.
To effectively fight climate change, emissions need to be cut from almost all parts of the economy.
What factors other than greenhouse gases might change the earth’s atmosphere?
Other natural factors affecting the atmosphere include volcanic eruptions and changes in the amount of solar radiation.
When volcanos erupt, they spew volcanic dust and other particles into the atmosphere, blocking sunlight from entering the Earth’s atmosphere.
They contribute to cooling the planet, with the effect lasting up to 2 years.
The angle of the Earth’s orbit around the sun is changing slightly about every 20,000 years. Gravitational forces also slowly change the Earth’s orbit over hundreds of thousands of years.
Changes in the Earth’s orbit affect the amount of solar radiation from the sun reaching the Earth.
This causes more, or less, warming of the Earth’s surface.
Factors resulting from human activities, such as greenhouse gas emissions, industrial pollution, and changes in agricultural land use, also affect the Earth’s atmosphere.
These are the factors that are leading to global warming and climate change.
Are we sure that it’s greenhouse gases that are heating the earth?
Yes. Scientific evidence is now conclusive.
In recent times, we have been significantly adding to the greenhouse gas concentrations in the atmosphere, feeding the greenhouse effect.
There is now a nearly one-to-one relationship between the amount of greenhouse gases in the atmosphere and the temperature on the earth’s surface.
The level of carbon dioxide in the atmosphere now stands at 413 parts per million, well above anything we have seen in the last million years.
Look at some scientific calculations which split global warming into its natural and manmade origins.
In the graph below, you can see three lines.
The top black line shows the actual increases in average global temperatures.
The bottom grey line is the amount of global warming that is explained by natural drivers – volcanos and changes in solar radiation from the sun.
You can see that this grey line stands at a much lower level of global warming than we see in reality. Natural drivers can only explain a small part of the temperatures experienced.
Only when we include the human drivers – shown by the second, higher grey line – does the level of global warming closely match the black line of reality.
We are warming the planet. Scientific evidence is now conclusive on that.
If we continue to increase the amount of greenhouse gases emitted to the atmosphere, it will continue to warm up through the greenhouse effect.
Of this, scientists are certain.
To keep warming below 1.5 degrees C above pre-industrial levels means that we have to reduce greenhouse gas emissions to net zero as soon as possible.
Read on to discover which countries are producing the most emissions, what net zero is and how for we have to go.