The enhanced greenhouse effect and global warming

Ecology and the environment · Human influences on the environment · note 3 of 6

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The enhanced greenhouse effect and global warmingSpec 4.15

In short

The enhanced greenhouse effect is the extra warming caused when human activities increase the amount of greenhouse gases. These gases absorb infrared radiation given out by the Earth and radiate it back, so more heat is trapped and the average surface temperature rises, called global warming. Consequences include rising sea levels, extreme weather and changes in species distribution.

Some greenhouse effect is natural and necessary. The enhanced greenhouse effect is the extra warming caused by human activities that increase the amount of greenhouse gases.

Radiation from the Sun passes through the atmosphere and warms the surface of the Earth.
The warm Earth gives out infrared radiation (heat) towards space.
Greenhouse gases in the atmosphere absorb some of this infrared radiation and radiate it in all directions, including back towards the Earth. This keeps the Earth warm.
When humans increase the amount of greenhouse gases, more infrared radiation is absorbed and sent back to the Earth. This is the enhanced greenhouse effect.
The average temperature of the Earth's surface rises. This is global warming.

Possible consequences of global warming

Ice caps and glaciers melt and the oceans expand as they warm, so sea levels rise. Low-lying coastal land can flood.
Weather patterns change, with more extreme events such as droughts, floods and storms.
Habitats change, so the distribution of species changes. Species that cannot move or adapt may become extinct, so biodiversity falls.
Crop yields may change in some regions, which affects food production.

Common mistake:

The greenhouse effect is not the same as the hole in the ozone layer. Do not mention ozone when explaining global warming.

Two panels: in the greenhouse effect, radiation from the Sun warms the Earth, some infrared radiation escapes to space and some is absorbed by a thin layer of greenhouse gases and radiated back to the Earth; in the enhanced greenhouse effect, a thicker layer of greenhouse gases sends more infrared radiation back and less escapes. — More greenhouse gases absorb more infrared radiation, so more heat is trapped and the Earth warms.

Written and checked against the Edexcel IGCSE Biology (4BI1) specification · Updated October 2026

Frequently asked questions

What is eutrophication and what causes it?

Eutrophication happens when too many mineral ions, such as nitrates and phosphates from fertilisers, are leached into lakes and rivers. Algae grow rapidly and block light, so plants below die. Decomposing bacteria feed on the dead material and use up the oxygen in aerobic respiration, so fish and other animals die.

How does deforestation affect the carbon cycle?

Biology only Deforestation raises the carbon dioxide concentration of the air. With fewer trees there is less photosynthesis, so less carbon dioxide is removed and less oxygen is released. Burning the felled trees releases carbon dioxide by combustion, and decay releases it by respiration of decomposers. This adds to the enhanced greenhouse effect.

How does the enhanced greenhouse effect cause global warming?

The Earth gives out infrared radiation, and greenhouse gases absorb some of it and radiate it back towards the Earth. Human activities, such as burning fossil fuels, increase these gases, so more infrared radiation is trapped. The average surface temperature rises, which is global warming, causing rising sea levels and more extreme weather.

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