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why greenhouse effect is important

Greenhouse gases’ are crucial to keeping our planet at a suitable temperature for life. Without the natural greenhouse effect, the heat emitted by the Earth would simply pass outwards from the Earth’s surface into space and the Earth would have an average temperature of about -20°C.

Greenhouse gases

A greenhouse gas is called that because it absorbs infrared radiation from the Sun in the form of heat, which is circulated in the atmosphere and eventually lost to space. Greenhouse gases also increase the rate at which the atmosphere can absorb short-wave radiation from the Sun, but this has a much weaker effect on global temperatures.

The CO2 released from the burning of fossil fuels is accumulating as an insulating blanket around the Earth, trapping more of the Sun’s heat in our atmosphere. Actions carried out by humans are called anthropogenic actions; the anthropogenic release of CO2 contributes to the current enhanced greenhouse effect[1].

Which gases cause the greenhouse effect?

The contribution that a greenhouse gas makes to the greenhouse effect depends on how much heat it absorbs, how much it re-radiates and how much of it is in the atmosphere.

In descending order, the gases that contribute most to the Earth’s greenhouse effect are:

  • water vapour (H2O)
  • carbon dioxide (CO2)
  • nitrous oxide(N2O)
  • methane (CH4)
  • ozone (O3)

In terms of the amount of heat these gases can absorb and re-radiate (known as their global warming potential or GWP), CH4 is 23 times more effective and N2O is 296 times more effective than CO2. However, there is much more CO2 in the Earth’s atmosphere than there is CH4 or N2O.

Not all the greenhouse gas that we emit to the atmosphere remains there indefinitely. For example, the amount of CO2 in the atmosphere and the amount of CO2 dissolved in surface waters of the oceans stay in equilibrium, because the air and water mix well at the sea surface. When we add more CO2 to the atmosphere, a proportion of it dissolves into the oceans.

Anthropogenic greenhouse gases

Since the start of the Industrial Revolution in the mid-18th century, human activities have greatly increased the concentrations of greenhouse gases in the atmosphere. Consequently, measured atmospheric concentrations of CO2 are many times higher than pre-industrial levels.

Overview of global man-made greenhouse gas
Information iconOverview of global anthropogenic greenhouse gas emissions in 2017; figures here are expressed in CO2-equivalents. Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2015 (EPA, 2017).

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