What is the greenhouse effect?
A natural phenomenon in which, after the Earth absorbs energy from the sun and re-emits it as heat (infrared radiation), greenhouse gases in the atmosphere absorb part of that heat and send it back toward the surface, raising the temperature. It is called the "greenhouse effect" because it works similarly to how the glass or plastic of a greenhouse traps heat to raise the temperature inside. This phenomenon itself is a natural and essential process that keeps Earth at a temperature suitable for life.
Major types of greenhouse gases
Carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), water vapor, ozone, and chlorofluorocarbons (CFCs) are considered the main greenhouse gases. Of these, water vapor naturally makes up the largest share, but carbon dioxide and methane β whose emissions have risen sharply due to human activity β are the most heavily discussed in recent conversations about warming. Each gas differs in its heat-trapping ability (global warming potential) and how long it stays in the atmosphere.
Natural greenhouse effect vs. human-enhanced greenhouse effect
Without the natural greenhouse effect, Earth's average temperature would be far lower than it is today, making it a difficult environment for life to survive in. The real problem is not the greenhouse effect itself, but the "enhanced greenhouse effect" β the far faster-than-before rise in greenhouse gas concentrations since industrialization, driven by fossil fuel use and deforestation, which is warming the planet beyond what is needed. For this reason, the greenhouse effect and global warming are related but are not the same thing.
How much has CO2 concentration increased?
Before industrialization, atmospheric CO2 concentration was around 280 ppm, but by the 2020s it is reported to have risen to around 420 ppm. This figure is continually updated through ongoing observation and can vary somewhat by season and measurement time, so for the most accurate and current figure, it's best to check the latest data from an authoritative source such as the Mauna Loa Observatory in Hawaii. Regardless, it is a widely agreed-upon fact that the level is significantly higher than before industrialization and continues to trend upward.
Feedback effects that accelerate warming
As temperatures rise, melting ice reduces sunlight reflectivity, and methane is released from thawing permafrost β these are examples of chain reactions discussed as further accelerating warming. Such feedback effects are considered an important topic in climate research, because rising temperatures and rising greenhouse gas concentrations can reinforce each other, potentially making the pace of change faster than expected.
Why it's easy to confuse this with ozone layer depletion
The greenhouse effect (a problem of trapping heat) and ozone layer depletion (a problem of a thinning UV shield) are two separate environmental issues with different causes and effects. However, some substances, such as CFCs, both deplete the ozone layer and are also powerful greenhouse gases, which is why the two issues are often mentioned together and easily confused. It helps to remember that ozone depletion is mainly linked to UV-related risks like skin cancer and cataracts, while an enhanced greenhouse effect is mainly linked to rising temperatures and extreme weather.
What would happen without the greenhouse effect at all?
If the atmosphere had no greenhouse gases whatsoever, Earth would be unable to retain heat, and its average temperature would be explained as far lower than today β an environment difficult for life to survive in. In fact, the Moon, which has almost no atmosphere, experiences an enormous temperature difference between day and night. This comparison helps illustrate that the greenhouse effect itself is not inherently bad β the problem is when it becomes excessively strong beyond a "proper" degree.