On this page, we look at the enhanced greenhouse effect including the human activities that cause it.
Key terms: GE, EGE, GCC and GW
The Greenhouse Effect (GE) is the warming of the Earth’s atmosphere that occurs thanks to gases such as carbon dioxide, nitrous oxide and methane that natural occur in the atmosphere.
The Enhanced Greenhouse Effect (EGE) is the increased severity of this natural effect after it has been enhanced by human activity which has added to the concentration of these gases in the atmosphere.
Global Climate Change (GCC) is the term given to the effects of the EGE. Climate change incorporates many aspects of climate, including:
- Average temperatures
- Wind patterns
- Wind speeds
- Humidity levels
- Seasonal variations in weather
- The intensity and frequency of severe weather events
Global Warming (GW) is just one aspect of Global Climate Change. Owing to the current climate forcings, many parts of the world will see an increase in temperatures. However this is not uniform. Some parts of the world will experience cooling or stable temperatures, while other climatic variations such as the intensity of rainfall will vary. For this reason, Geographers avoid the term Global Warming’ as it is an oversimplification of the climate and suggests the only outcome of the EGE is higher temperature.
An important note about climate and weather
Climate and weather are not the same thing. Climate is the average conditions of the atmosphere, while weather is the short-term changes in the atmosphere. Weather is a ‘snapshot’ of what is going on over a short period of time – e.g. whether it rains on any given day. But climate is a much longer average. It is usually taken over a minimum period of 30 years and can be an average of atmospheric conditions over much longer periods.
The Enhanced Greenhouse Effect
As stated above, the EGE is a stronger version of the natural greenhouse effect.
The greenhouse effect
The surface of the earth is much cooler than the sun so the wavelength of the radiation is much longer, i.e. longwave radiation. It can’t pass through the atmosphere as easily, so a lot of it is absorbed and then reradiated back to earth. It gets stored long enough to raise the temperature of the atmosphere. This is the natural greenhouse effect and is shown in the diagram below.
- The Greenhouse Effect. Souce: Trenberth, Fasullo and Kiehl, 2009. Reproduced under Creative Commons licence for reuse.
The most prominent greenhouse gas is carbon dioxide. Carbon dioxide levels are at a historic high as shown on the graph below.
- Historic variations in the amount of carbon dioxide in the atmosphere. Source: NASA, 2018a.
The result of this increase in greenhouse gases is higher atmospheric temperatures. However, just because the average temperature is rising does not mean that temperatures everywhere will rise; also, the temperature is just one aspect of climate change in addition to things like wind, humidity and preciptiation.
- Historic variations in the temperature of the atmosphere. Source: NASA, 2018b.
General causes of the EGE
The reason for the extra gases in the atmosphere is believed to be human activities. There is a scientific consensus that human activities are causing the vast majority of the current period of warming. (See Bloomberg graphics for an excellent visualisation of the level to which natural climate forcings may be responsible versus human activities that increase greenhouse gases (Roston and Migliozzi, 2015).)
Human activities that cause the increase in greenhouse gases, and therefore climate changes, are known properly as anthropogenic causes. These include:
- Burning fossil fuels for electricity
- Burning fossil fuels for transport
- Deforestation and the loss of a key carbon sink
- Arable agriculture
- Pastoral agriculture
The graph below shows the emissions by humans by types of gas. The amount of gas being released into the atmosphere is steadily increasing over time, with the majority made up of carbon dioxide from burning fossil fuels.
- Anthropogenic greenhouse gas emissions. Source: Plumer, 2014.
In the United States, most of these gases are from transport, industry and electricity production, as shown on the graph below.
- Sources of Greenhouse Gas Emissions in the USA. Source: EPA, 2015
Similar proportions are to be expected in most High Income Countries (HICs). These are discussed in more depth in the next section of this site.
Specific causes of the EGE
Burning fossil fuels for electricity and transport
Fossil fuels are:
- Natural gas
Fossil fuels are the fossilised remains of living organisms, all of which are carbon-based. They are formed over millions of years due to compression in the Earth’s crust. When these fuels are burned, the carbon that was ‘locked up’ inside them underground is released, where it joins oxygen to form carbon dioxide (among other greenhouse gases).
The reason for burning these fuels is the thermal generation of electricity. Also the vast majority of vehicles – including cars, ships and aeroplanes – burn fossil fuels in the form of petroleum (oil). Fossil fuels are a popular energy source because they are reliable, relatively cheap and the technology is well understood around the world.
Deforestation and the loss of a key carbon sink
Deforestation can be defined as the loss of trees. Humans remove trees for many reasons including creating space for agriculture, to use the timber as a product, and for urbanisation including transport. When trees are burned, they release carbon. However, because they have absorbed that carbon relatively recently, the burning of an individual tree doesn’t make that much difference. This is why biofuels are a potential solution to climate change – the gas they release when burned has only been removed from the atmosphere a short time ago, so the overall impact is small. It’s when entire continents of forest are threatened that it becomes a problem.
This is mainly because forests are a carbon sink. A carbon sink is a store of carbon that is removed from the atmosphere. Forests are a carbon sink because they absorb carbon from the atmosphere and lock it up inside them. When this potential store of carbon is removed, the carbon is no longer absorbed from the atmosphere and can build up again in the atmosphere.
Arable and pastoral agriculture
Arable agriculture (farming crops like wheat and vegetables) has a huge impact on climate change, because rice fields are a huge source of methane gas. Pastoral agriculture (rearing animals, such as cows for beef and milk, and pigs for pork) is also a huge contributor because:
- Land must be cleared for the animals to graze
- Animals must be fed, so the impacts of arable agriculture must be added to their contribution
- Animals themselves are a large source of gases such as methane that is produced in the digestive system of animals
- Often the animals are reared a long way from where they are consumed, adding in huge transportation emissions
In addition to all these direct causes, humans also have indirect effects on the atmosphere due to feedback loops. Once more greenhouse gases heat up the atmosphere, there is a chain reaction of effects that further enhance the greenhouse effect. These include the melting of ice, the decrease in cloud, and the rise in sea levels which all affect the albedo of the planet. The decrease in albedo leads to further climate change.
EPA [United States Environmental Protection Agency], 2015. Sources of Greenhouse Gas Emissions. https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions Accessed 31 January 2018.
NASA, 2018a. Carbon Dioxide: Proxy (Indirect) Measurements. https://climate.nasa.gov/vital-signs/carbon-dioxide/ Accessed 22 February 2018.
NASA, 2018b. Scientific consensus: Earth’s climate is warming. https://climate.nasa.gov/scientific-consensus/ Accessed 22 February 2018.
Plumer, 2014. IPCC: We can still stop global warming — but it’s going to be tough. ttps://www.vox.com/2014/4/13/5610356/un-panel-heres-how-we-cut-emissions-and-avoid-a-climate-disaster Accessed 31 January 2018.
Roston and Migliozzi, 2015. What’s Really Warming the World? https://www.bloomberg.com/graphics/2015-whats-warming-the-world/ Accessed 31 January 2018.
Trenberth, K. E., J. T. Fasullo, and J. Kiehl, 2009: Earth’s global energy budget (PDF). Bull. Amer. Meteor. Soc., 90, No. 3, 311-324. This image viewed via https://commons.wikimedia.org/wiki/File:The_green_house_effect.svg Accessed 23 January 2018.
The enhanced greenhouse effect: Learning activities
- Define the following terms:
- Greenhouse effect 
- Enhanced greenhouse effect 
- Distinguish between global climate change and global warming. 
- Distinguish between the meaning of weather and climate. 
- Explain why many Geographers prefer not to use the term ‘global warming’ when discussing global climate change. 
- Describe the variation in carbon dioxide within the atmosphere over the past 400,000 years. 
- Define ‘anthropogenic’. 
- Identify four gases that are produced by humans. 
- Outline how these gases are produced. Refer to at least three human activities in your answer. [3+3+3]
- Explain how anthropogenic activities could continue to cause global climate change, even if they were all halted immediately. (Tip: This question is about feedback loops.) 
Right now, look around. Think very carefully about everything you can see, hear, smell, touch and taste. What impact are you having on climate change at this very moment? Describe each way in which you might be contributing to climate change and identify ways in which you could reduce your impact. Remember, for changes to be sustainable they must not only protect the environment but also create social and economic benefits too – so you can’t switch off your laptop and go and play hockey to save electricity, as that would reduce your educational success in the long run!