What are greenhouse gases (GHGs)?

Greenhouse gases are a set of gases called such because they trap heat in the Earth’s atmosphere, contributing to the “greenhouse effect” which leads to global warming. They do this by absorbing sunlight that bounces back off the Earth as heat, trapping this heat close to the planet instead of it being reflected back into space.

GHGs are emitted from various different sources, both natural and as a result of human activity. However, human activity since the industrial period (in the mid-19th century) has greatly increased the amount of these gases in our atmosphere, significantly contributing to global warming and subsequent climate change. For their role in accelerating climate change, GHGs are therefore a form of air pollution that is a crucial environmental concern. However, given their significance to global environmental change, they are often treated as a separate issue to other air pollutants, which have more local effects on health and environment.

Main GHGs include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases (or F-gases).

Where do they come from?

Natural sources include decomposition of organic matter, wetlands (methane), respiration, and soils. Fluorinated gases are the only GHGs that are purely human-generated.

Various human activities generate GHG emissions. Burning fossil fuels is a key contributor which is commonly targeted by environmental policies. Sectors that significantly contribute to emissions include:

• Electricity generation
• Transportation
• Industry
• Commercial and residential (heating, etc)
• Agriculture
• Land use and forestry

How do they affect our health?

Individual GHGs can have detrimental health effects, such as the risks CO2 poses in high indoor concentrations. However, grouped together on the basis of their contribution to the greenhouse effect, GHGs mainly pose a health threat through their contribution to climate change, which may radically alter our planet’s environment in detrimental ways to human life. Some health threats posed by climate change include heat waves, tainted drinking water supply, displacement of people, and the dangers of flooding.

Environmental effects?

GHGs’ contribution to the greenhouse effect, global warming and climate change has severe environmental consequences which will affect the planet and humans alike. Rising global temperatures mean ice caps and glaciers will melt, causing sea levels to rise and potentially displace huge numbers of people. Other consequences of climate change include increased likelihood and severity of forest fires; extended droughts; flooding; a threat to existing ecosystems and species’ survival under new climate conditions; and disruption of the global food supply.

Climate change is also predicted to increase concentrations and lingering durations of ground-level ozone pollution.

Read more about the interaction between climate change and air pollution here.