The greenhouse effect: Counting gases and why it matters

What is the greenhouse effect?

The sun radiates energy, part of which is absorbed by Earth, and the rest bounces back into space. However, greenhouse gases in the Earth’s atmosphere trap some of this reflected energy, preventing it from entirely escaping into space, and thereby contributing to the heating of our planet. This natural warming process can be observed on Earth and on other planets within our solar system. This is a very simple greenhouse effect definition. Let’s dig a little deeper into what causes the greenhouse effect?

How does the greenhouse effect work?

The greenhouse gas effect is caused by certain gases called greenhouse gases. The molecules of greenhouse gases absorb and reemit thermal radiation, much like a tuning fork absorbs and reemits sound waves tuned to its frequency. Greenhouse gas molecules release some of this thermal radiation back to Earth’s surface, contributing to the build-up of heat. A simple greenhouse effect diagram can be helpful to describe the greenhouse effect, and what greenhouse gases are doing to the Earth’s atmosphere.

What are greenhouse gases?

Greenhouse gases are – for the most part – a natural phenomenon; they trap heat from sunlight reflecting off Earth’s surface. For more than ten thousand years, during the epoch that saw humanity evolve from hunter gatherers to agricultural and urban civilizations, the concentration of greenhouse gases in the atmosphere remained relatively stable, maintaining Earth’s surface temperature at a warm level.

So, which gases contribute to the greenhouse effect? While they come in many forms, the following are the main examples of greenhouse gases:

• Carbon dioxide (CO₂): Accounting for almost 80 % of global human-caused emissions, carbon dioxide can stick around for quite a while. Some CO₂ is absorbed quickly, but some will remain in the atmosphere for thousands of years.
• Methane (CH₄): Methane persists in the atmosphere for around 12 years, which is less time than carbon dioxide, but it is much more potent in terms of the greenhouse effect.
• Nitrous oxide (N₂O): Nitrous oxide is a powerful greenhouse gas. It has a global warming potential which is around 270 times that of carbon dioxide on a hundred-year time scale, and it remains in the atmosphere, on average, a little more than a century.
• Fluorinated gases: Emitted from a variety of manufacturing and industrial processes, fluorinated gases are human-made. There are four main categories: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF₆), and nitrogen trifluoride (NF₃).
• Water vapour (H₂O): This is by far the most abundant greenhouse gas. Water vapour differs from other greenhouse gases in that the changes in its atmospheric concentrations are not linked to human activities directly, but rather to the warming that results from the other greenhouse gases we emit.

By increasing the concentration of greenhouse gases in the atmosphere, we’re amplifying Earth’s natural greenhouse effect and turning up the dial on global warming and climate change.

Why does a car get hot in the sun?

Let’s take a couple of greenhouse effect examples: the sun warming a car and the sun warming a greenhouse. Visible light penetrates through the glass and warms the objects within. These objects absorb the light, and then radiate back to the air infrared light, as a way to release the energy. This infrared light, which can be felt as heat, has too long of a wavelength to pass back through the glass, getting trapped inside the car or greenhouse. This phenomenon is known as infrared radiation, and it explains why a car gets hot when it sits in the sun.

So, is the greenhouse effect good for us as human beings? Greenhouses work well to offer a good habitat for growing plants because they let the visible light in but trap the residual heat. However, trapping too much heat can be dangerous, the single most important example of this being global climate change.

What do we mean by a runaway greenhouse effect?

We can learn a lot about climate change from our sister planet Venus, Earth’s nearest neighbour. Venus currently has a surface temperature of 450 °C (hot enough to turn lead to liquid, NASA scientists say) and an atmosphere dominated by 96 % carbon dioxide – making it a burning inferno. But it wasn’t always that way. In fact, at one time, it may have had an Earth-like climate.

What happened on Venus? Several billion years ago, a runaway greenhouse effect turned all surface water into vapour, which then leaked slowly into space. This occurs when a planet absorbs more energy from the sun than it can radiate back to space.

Could this scenario happen on Earth? Even burning all of the planet’s fossil fuel resources, according to some scientists, would not necessarily take us down the road toward a climate meltdown. By studying why Venus’s climate went in such a different direction with regard to habitability, we can probably learn valuable lessons about climate change – and avoid reaching the point of no return.

In simple terms, “tipping points” in climate change are synonymous to a seesaw. Just as a little weight can tip a seesaw and make it difficult to return to its original position, in the climate system, tipping points represent critical levels where small changes can lead to big and often irreversible shifts in weather patterns. Once these points are crossed, they can cause a chain reaction, with more emissions entering the atmosphere. For example, thawing permafrost releases methane, and wildfires increase carbon dioxide levels.

Standards solutions

To avoid unpredictable and uncontrollable changes in climate, humanity needs to act swiftly and in coordination, implementing comprehensive strategies to reduce carbon emissions, conserve biodiversity, and transition towards sustainable living globally. An important tool for informed action is to monitor Earth’s temperature and greenhouse gas emissions carefully.

The good news is governments and organizations can now back net-zero commitments by credible action using ISO standards. For example, ISO 14064 is an International Standard for greenhouse gas accounting and verification. It provides organizations with a framework for measuring and reporting greenhouse gas emissions, as well as for verifying emission reductions and removals. This multi-part standard is an important tool to ensure transparency and uniformity across global efforts to combat climate change.

• ISO 14064-1:2018Greenhouse gases
• ISO 14067:2018Greenhouse gases — Carbon footprint of products
• ISO 14068-1:2023Climate change management — Part 1: Carbon neutrality

Avoiding greenhouse effect chaos

Today, concentrations of human-caused greenhouse gases in the atmosphere are higher than ever and the planet is heating up. The good news is that we have the ability to rein in greenhouse gas emissions – by overhauling our energy systems, habits and lifestyles.

Understanding the greenhouse effect and the role of different gases is pivotal to mitigating the impacts of climate change. By adhering to International Standards to measure and report our emissions, we guarantee that our efforts are as effective and coordinated as possible. For just as the greenhouse gas emissions from a century ago still contribute to the climate change we see today, the emissions we release today will continue to impact us long into the future.