What is the greenhouse effect?

The greenhouse effect is a natural process whereby the Earth’s atmosphere insulates the planet and keeps it warm. (Space is really, really cold.)

The Earth is warmed by a combination of incoming and outgoing radiation. Like Baby Bear’s porridge, it’s just right – not too hot and not too cold. That’s one reason why it’s comfortable for so many different life forms, unlike other planets in our solar system, which are either scorching or freezing.

However, keeping the outgoing and incoming radiation roughly equal is a delicate balancing act.

The incoming radiation is mostly generated by the sun, in the form of visible light, plus invisible types of radiation such as ultraviolet (UV) and infrared (IR).

Nearly a third of this solar radiation is immediately reflected back into space as outgoing radiation, by clouds, sand, ice, snow and any other reflective surfaces. That’s why some scientists trying to lessen the impact of global warming [link to new ‘How to stop global warming’ article] suggest that we paint all roofs white, and use light-coloured materials to surface roads and pavements, so that we create more reflective surfaces.

The rest of the incoming radiation is absorbed into the sea, land and air, heating them up. They release this heat as infrared thermal radiation, and send it back into space.

However, our planet is wrapped in a layer of gases – the so-called ‘greenhouse gases’. The effect of these greenhouse gases is to make sure some of this heat stays within our atmosphere to keep us warm and safe. This natural phenomenon makes our planet habitable.

Greenhouse gases don’t absorb visible sunlight, but can absorb and emit infrared radiation. That means most of the sun’s energy can pass through the covering to warm the Earth’s surface. However, this energy is unable to pass back through the gases into the universe – so the planet stays warm. This is what’s called the greenhouse effect, and without it, Earth could eventually become too hot or too cold to sustain life.

It’s defined as the greenhouse effect because it works in much the same way as a greenhouse’s glass walls. Incoming ultraviolet light can pass easily through greenhouse glass and then be absorbed by the plants inside as heat. However, the outgoing radiation is much weaker and can’t get back through the glass walls. So it’s trapped inside, creating a warm atmosphere for the plants.

Why is the greenhouse effect no longer a good thing?

Unfortunately, human activity is creating too many greenhouse gases, and they are creating an enhanced greenhouse effect. This is adding to the insulation of the planet, warming it overall and causing changes in the climate that we can’t predict.

What are the greenhouse gases?

The greenhouse gases include:

  • Carbon dioxide (CO2)
  • Chlorofluorocarbons (CFCs)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • Ozone (O3)
  • Water vapour

These gases occur naturally in the environment, but human activity is increasing their concentration and scientists are particularly concerned about the impact carbon dioxide is having on the greenhouse effect.

Humans do things like burning coal and oil – which creates carbon emissions (see below) – and cutting down trees that absorb carbon dioxide, so there are an increasing number of greenhouse gases in the atmosphere. The more greenhouse gases in the atmosphere, the thicker the layer around the Earth becomes, and the higher the average temperature of the planet becomes.

The greenhouse gas effect is a key driver in climate change, which is the large-scale, long-term shift in the planet’s weather patterns and average temperatures. While planet Earth has seen fluctuations between tropical climates and ice ages over its 4.5-billion-year history, Earth’s average temperature is now rising rapidly. The knock-on effects of this include changing weather patterns, melting ice caps, rising sea levels and changes to ecological environments, which could have serious effects on the habitability of the Earth for humans in future.

What are carbon emissions?

When working out the carbon footprint [link to new ‘What is a carbon footprint?’ article] of a person, activity, item, company, lifestyle or nation, we start by working out how much carbon dioxide (CO2) it creates. We then consider whether it generates other greenhouse gases, like those shown above. Rather than showing the amount of each separate gas, the total amount is usually shown as CO2e – where ‘e’ stands for ‘equivalent’ and shows the effect of all these gases cumulatively. Together they are known as ‘carbon emissions’.

Driving, flying and warming our homes all affect the environment, because they generate carbon emissions, which scientists believe are a major cause of climate change

Can the greenhouse effect be slowed down or reversed?

Many governments around the world are trying to minimise the effect of climate change by introducing policies that will reduce the concentration of greenhouse gases in our atmosphere.

In the meantime, we can all do our bit by trying to reduce our individual carbon footprints. We can do this by cutting back on activities that increase carbon emissions, such as driving or using excess packaging, or by positive actions like recycling or installing solar panels.

Which activities cause most greenhouse gases?

According to Mike Berners-Lee ‘How bad are bananas? The carbon footprint of everything’ (Profile Books, 2010), some of the worst offenders are volcanos, The (football) World Cup, the world’s data centres, bushfires and wars, all of which generate over 1 million tonnes of CO2e or more*.

However, as an individual you don’t have much power to stop any of these things, particularly volcanos. So what are the activities you could cut back on?

It makes sense to try and reduce long-haul air travel, buy a second-hand car rather than a brand new gas-guzzler, stop wasting heat and energy in your home, and make sure you dispose of your rubbish properly.

Easy ways to reduce your carbon footprint

On the whole, the ways you can help to slow down the greenhouse effect are the same as the ways you can make your home more energy efficient and cut down your energy bills. So they’re beneficial for you as well as for the Earth’s atmosphere.

For example, you could:

  • Try to eat less meat, and choose local or organic products whenever possible.
  • Insulate your home – particularly your loft. Install double or triple glazing, fill cavity walls, and use draught excluders.
  • Rather than use your car, try to walk or bicycle, take public transport and look into car-sharing opportunities.
  • Replace your old light bulbs with energy-efficient ones.
  • Re-use and recycle as much as you can – if one household recycles at least half of its waste, that can save around 1.2 tonnes of carbon dioxide each year.
  • Think about slowing down from 70 mph to 60 mph on motorways.
  • Switch appliances off at the wall when they’re not in use.
  • Try turning down your heating thermostat by 1oC – you could put on an extra sweater instead.


*Mike Berners-Lee ‘How bad are bananas?’ Profile Books Ltd 2010

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