What Are Greenhouse Gas Emissions?

The main GHG emissions are those from CO2, methane, nitrous oxide and chlorofluorocarbons. The biggest man-made sources are coal, petroleum, natural gas, wood and peat. Wildfires, soil and wetlands are major natural sources. We provide a full explanation.
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Greenhouse gas emissions from industrial plants. Photo: © Chris LeBoutillier/Unsplash

In the context of global warming, the term “greenhouse gas emissions” refers to man-made discharges of greenhouse gases that gather in the lower atmosphere, where they trap heat given off by the planet, in a process known as the “greenhouse effect.” Most of these heat-trapping gases are created by the burning of fossil fuels, like coal, peat, oil and natural gas, or through industrial processes such as the manufacture of steel. Cement industry CO2 emissions are also huge

The most common man-made greenhouse gas is carbon dioxide (accounting for about 82 percent of U.S. emissions), while others include methane (10 percent), nitrous oxide (6 percent), as well as a number of fluorinated gases (3 percent) such as hydrofluorocarbons and sulphur hexafluoride (SF6). 1

The excess heat trapped by greenhouse gases (GHGs) is the No 1 cause of our climate crisis, whose adverse effects include extreme weather events, wildfires, sea-level rise, loss of marine and terrestrial biodiversity, and disrupted water systems. 2

According to the IPCC, in order to limit rising temperatures to a relatively manageable 1.5°C, global greenhouse gas emissions must fall 45 percent (compared to 2010 levels), by 2030, and to ‘net zero’ by 2050. Right now, however, given the lack of any coherent climate change mitigation strategy by the global community, the planet looks set to reach 3°C by the end of this century. An outcome which is likely to have very serious effects on Planet Earth and its biosphere. 2

Read our article: How To Reduce Your Carbon Footprint.

Sources of Greenhouse Gases

Greenhouse Gas Emissions 2020
Total 59.1 billion tons of CO2 equivalent. 38.0 billion tons (72.6%) came from fossil fuels and industry; 9.8 billion tons came from man-made methane emissions (18.7%); 2.8 billion tons came from man-made nitrous oxide emissions (5.4%); and 1.7 billion tons came from fluorinated gases (3.3%). A further 6.8 billion tons came from deforestation and land use. Source: UN Emissions Gap Report 2020

Difference Between Natural And Man-Made Emissions?

When analyzing climate change, it’s important to understand the difference between natural greenhouse gas emissions and the man-made variety. Natural emissions include the discharge of carbon dioxide from plants (respiration) and forest fires, as well as methane from wetlands. These naturally occurring GHGs have been an important part of Earth’s climate balance for thousands of years. During this time they have kept the planet’s temperature at a cosy 15°C (59°F). Without this natural greenhouse mechanism, Earth’s average temperature would be a frosty minus 18°C (0 °F). So, the natural greenhouse effect along with the natural levels of GHG that make it happen, are fine. 3

But man-made GHGs are a different story. Their sudden appearance has upset the balance and triggered a rise in Earth’s temperature. This climate change hasn’t happened overnight – it has taken more than 250 years to get going – but now it’s beginning to pick up speed and we need to respond quickly, before it causes irreparable damage to the planet. What’s the best way to tackle the problem? By dealing with its No 1 cause – the burning of fossil fuels, like coal, peat, petroleum and natural gas, whose emissions of carbon dioxide (CO2) and other heat-trapping gases are doing such damage to our climate. 4 5

“Concentrations of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) now substantially exceed the highest concentrations recorded in ice cores during the past 800,000 years.”

Intergovernmental Panel on Climate Change. Fifth Assessment Report (2014)

What Causes Greenhouse Gas Emissions?

The primary cause of greenhouse gas emissions is the burning of fossil fuels. It all started with the Industrial Revolution (c.1750-1850). This revolution was built on two things: (a) the invention of new machines and engines that could do the work of hundreds of human workers; and (b) accessible supplies of fossil fuels, like coal, to power the machines. Later, the internal combustion engine revolutionized the transport process (then based entirely on boats and animal power) which opened up whole continents for the benefit of trade and personal movement.

During the course of two centuries (1750-1950), developments in industry and transport brought unimaginable progress to every corner of the globe. As a result, the world’s population soared. In 1760, it was 770 million; by 1900, it was 1.6 billion; by 2000, 6.1 billion.

However, to power this industrial progress and produce the billions of items needed to support developing societies, gargantuan amounts of fossil fuels have been searched for, mined and burned. In turn, this has created a massive accumulation of greenhouse gases in the atmosphere, a significant proportion of which (up to 20 percent) will remain there for thousands of years.

Cows produce methane emissions
Animal livestock are responsible for 14.5 per cent of global greenhouse gas emissions. The majority comes from beef and milk production, largely because cattle emit so much methane through flatulence and belching. Image: Livestock at the Irish National Ploughing Championships. CC-SA-3.0

At present, the most damaging activity is the burning of fossil fuels in power plants, factories and car engines. Other high-emission practices include: (a) cement manufacture (CO2); (b) livestock farming (methane); (c) the production, storage and transport of oil and gas (methane); and (d) the use of nitrogen-based fertilizers (nitrous oxide). All these activities lead to higher concentrations of GHG in the atmosphere, resulting in more heat being trapped and an accelerating rise in Earth’s temperature.

Carbon Emissions Statistics by Source

Carbon Dioxide Emissions per Unit of Energy

Carbon Dioxide Emissions per Unit of Energy
Carbon Dioxide Emissions of Different Fossil Fuels. Source: U.S. Energy Information Administration (2019) 6

How Do Greenhouse Gases Affect Feedbacks And Tipping Points?

Climate feedbacks are mechanisms that indirectly increase or reduce the impact of global warming. Take water vapor, for instance. This is a natural greenhouse gas and so does not cause warming. However, it does, indirectly, boost the effect of warming. Because warmer air holds more water, and more water in the air means more heat is trapped. Which raises the air temperature even more, and so on. In other words, as man-made greenhouse gases warm the atmosphere, they trigger feedbacks like extra water vapor that automatically boost the warming effect further.

Climate tipping points are irreversible changes in the climate system. Take the melting of polar ice sheets, for instance. Polar ice sheets are precious for two main reasons. First, their albedo reflects sunlight back out into space, thus contributing to the natural climate state. Second, they hold a gigantic supply of freshwater, which, if released (due to ice melt), would raise sea-levels and increase the risk of inundation in low-lying coastal areas around the globe.

Theoretically, there is a degree of ice-melt that forms an irreversible tipping point, beyond which nothing can stop all the ice melting. So even if man-made greenhouse gas emissions cease altogether, the ice will continue to melt until it is all gone. No one knows when this tipping point might be reached, which means we may cross it without realizing.

Other tipping points suggested by climate models include: the irreversible thawing of the northern permafrost triggering a gigantic release of methane gas, and the irreversible collapse of the Amazon rainforest biome along with its unique biodiversity and ecosystems. 7

Greenhouse gas emissions are acknowledged to be the main driver of climate change. 8 If they are not reduced quickly enough, they will trigger more climate feedbacks and may even cross a catastrophic tipping point.

What Determines The Effect of Greenhouse Gases?

The effect of each gas on global temperature is determined by three main factors: (a) How much of it is in the atmosphere? (b) How long does it remain active? (c) How much heat energy can it absorb and then re-radiate? The answers to these questions will determine the gas’s “global warming potential” (GWP). A gas’s GWP rating is usually assessed in relation to a specific time period, typically 100 years. In addition, all GWPs are measured in relation to carbon dioxide, which has a GWP of 1. Thus, if a gas has a GWP of 10, it means that it has 10 times the heat-trapping power of CO2.

Take methane gas, for example. Methane (CH4) is the second most prevalent man-made GHG in the atmosphere after carbon dioxide. But although methane’s active lifetime in the atmosphere (12 years) is much shorter than CO2’s, CH4 is much more efficient at trapping radiation than CO2. Indeed, CH4 has a GWP of 28, meaning it is more than 28 times more effective than CO2 over a 100-year period. 4

What Are Negative Greenhouse Gas Emissions?

The term “negative greenhouse gas emissions” refers to the REMOVAL of GHGs as opposed to the EMISSION of GHGs. It means taking GHGs out of the atmosphere instead of putting them in. It refers to a number of new carbon capture and storage technologies (such as “carbon capture and utilization”, “bio-energy with carbon capture and storage”) whose objective is the large-scale removal of CO2 from the atmosphere. (Note: CO2 is by far the most common GHG accounting for roughly 82 percent of man-made emissions; in addition, CO2 is the only greenhouse gas so far for which negative emissions are feasible at scale.)

Why are negative emissions so important? Because scientists don’t think that global warming can be stopped without it. We still need to make dramatic cuts in the amount of GHG we put into the atmosphere, but climate scientists think that these reductions won’t be enough to slow down the rise in temperature. Furthermore, in some sectors, like agriculture and aviation, reducing emissions to zero may not be feasible. So, the only approach is to extract sufficient greenhouse gases from the atmosphere in order to balance out the emissions that remain – an outcome known as “net-zero” emissions. In their Special Report on Global Warming of 1.5°C (2018), the IPCC outlines four options for limiting warming to 1.5°C. All use carbon dioxide removal techniques in order to achieve “net-zero” emissions as early as 2050.

How Is Carbon Dioxide Removed From The Atmosphere?

There are two main options: natural climate solutions (NCS) and negative emissions technologies (NETs). Neither is perfect. Natural climate solutions include tree planting (afforestation and reforestation), restoration of peat bogs and mangrove forests, and other CO2-trapping ecosystems.

The most controversial negative emissions technology is bioenergy with carbon capture and storage (BECCS). Plants are grown to absorb CO2 from the air. Then they are burned to generate electricity, and the CO2 given off is captured and stored underground. More plants are then cultivated, absorbing more CO2 from the air. This too is burned, and so on. Unfortunately, this technique is embroiled in land use controversy due to possible shortages in the amount of land available for planting.

Another NET is direct air capture (DAC), in which a chemical process extracts CO2 from the air.

Moringa trees being planted in Guinea to help absorb CO2 greenhouse gas emissions.
Moringa trees being planted by women in an agriculture cooperative on the Tristao Islands, Guinea. This reforestation helps remove CO2 from the air, supports biodiversity and helps prevent soil erosion. Photo: © UN Women/Joe Saade / (CC BY-NC-ND 2.0)

What Are The Effects of Greenhouse Gas Emissions?

Over time, rising concentrations of GHGs produce an increase in the Earth’s average surface temperature. This leads to extreme weather patterns, rising sea levels, ocean acidification, loss of animal habitats, and much more. These effects are known collectively as climate change. For more details, see our in-depth articles: What are the Effects of Global Warming? and What are the Effects of Global Warming on Humans? For facts and information about the impact of the coal, oil and gas industries on the planet, see: What are the Environmental Effects of Fossil Fuels?

When Did Man-Made Greenhouse Gas Emissions Start?

Britain was the world’s first large-scale emitter of greenhouse gases, beginning around 1750. Other European countries followed Britain’s lead shortly after, while America’s contribution only took off in the second half of the 19th century. Other regions, like Latin America, Africa and Asia, followed from the early 20th century onwards. For more on this topic, see: When Did Global Warming Start?

Analyzing GHG emissions during the present era, after peaking at 40 percent of all emissions in 1950, the USA has now been overtaken by China, with India, Russia, Japan and Brazil trailing some way behind. Asia is now the largest source of global emissions, mainly because it’s now the world’s No 1 manufacturer, making products that used to be manufactured in Europe and North America. However, it’s a firm principle of the United Nations Framework Convention on Climate Change that developing countries should be allowed to complete their economic development, even if it means that their emissions will rise in the interim.

How To Reduce Greenhouse Gas Emissions?

  • Invest more in fossil fuel replacements
    Institute a crash program of investment in renewable and sustainable sources of energy. The IPCC is calling for US$2.4 trillion to be invested in renewable energy, every year to 2035. 2
  • Switch to electrically powered vehicles
    When driven, electric vehicles (EVs) emit no pollution and, provided their batteries are recharged using clean sources of energy, account for zero carbon emissions.
  • Get tough with the big polluters
    In an interesting response to the IPCC’s Special Report on Global Warming of 1.5°C (2018), Kevin Anderson – Professor of Energy and Climate Change at the University of Manchester and a former Director of the Tyndall Centre for Climate Change Research – states that nearly half of all global CO2 emissions are caused by the activities of about 10 percent of the population. If we imposed a limit on the per-capita carbon footprint of these top 10 percent of global emitters – roughly equivalent to the footprint of an average European citizen – Anderson believes that global emissions could be reduced by one third in a matter of a year or two. 9
  • Carbon taxes
    Provided cleaner energy alternatives were in place, carbon taxes provide obvious incentives for companies and consumers to choose greener behaviors. Revenues from carbon pricing can be used to increase investment in climate change adaptation measures, including energy conservation, thus making the taxes more socially acceptable. 10 There is a consistently high level of public support for this approach. 11
  • Conservation measures
    This type of climate change adaptation is extremely important over the long term. The more energy we can conserve, or avoid using, the less energy (and emissions) we need to produce. A proper conservation campaign must involve the whole community (country or even world). Schools need to promote a more energy conscious attitude; manufacturers and retailers need to rely less on throwaway materials in packaging and point of sale. Homeowners and landlords should be encouraged to insulate their buildings and switch to clean energies. Energy consumption also needs to be tackled, which won’t be easy. But with 3.5 billion newcomers expected on the planet by 2100, the freedom to consume needs to be moderated, for the sake of everyone. 

The coronavirus shutdowns during the spring and summer of 2020 led to dramatic falls in greenhouse gas emissions over China, India and elsewhere. However, any beneficial effect of COVID-19 on climate change is not likely to be permanent.

How To Reduce Emissions of Carbon Dioxide?

  • Phase out subsidies for fossil fuels
    To scale back emissions of carbon dioxide, we need to stop encouraging the development, production and use of all fossil fuels. The only subsidies worth maintaining are those relating to environmental clean-up and disposal of contaminated waste. The oil industry’s tar sands developments in Alberta Canada are a particular case in point.
  • Provide financial incentives for new CO2 technologies
    Power plants emit huge amounts of CO2, as do cement factories and other industries. Capturing carbon dioxide from the stacks of a coal-fired or gas-fired power plant before it enters the atmosphere, is a vital part of any program to reduce industrial emissions. But investment in it lags. Governments need to find ways of boosting investment in this area.
  • Provide financial incentives for renewable fuels
    Although solar energy, offshore/onshore wind power, organic biomass, underground geothermal energy and hydropower are now well established, the continuing development of renewable energy from wave power and tidal power, as well as hydrogen-based fuels, must remain a top priority. We must remember that the technologies that ultimately prove successful may not yet exist. To find them requires a major effort which is best coordinated by national authorities.
  • Switch to electric vehicles (EVs)
    Electric buses and other public utility vehicles are fast becoming a regular sight in many urban areas. However, until a comprehensive network of battery charging points is established, many consumers are unlikely to switch to fully electric cars. What’s more, it remains to be seen whether current reserves of lithium or other similar metals will be sufficient to meet global demand for EVs. Some calculations suggest these may last less than 20 years. 12

How To Reduce Emissions of Methane?

  • Methane from livestock digestion can be reduced through modifications in animal feeding practices. 13
  • The oil and gas industries need to introduce wide ranging upgrades to their infrastructure (wells, refineries, storage tanks and pipelines) to reduce the huge financial and environmental costs of methane leakage. 14
  • Methane from landfill waste sites can be neutralized using carbon capture technologies.

How To Reduce Emissions of Nitrous Oxide?

Emissions of nitrous oxide from nitrogen fertilizers can be reduced by switching to more chemically benign formulae, and by improving animal manure management. Also rice agriculture needs more careful management. 15 Since nitrous oxide is also a by-product of fuel combustion in motor vehicles, switching to electric cars and buses should also reduce N2O emissions. 

How To Reduce Emissions of F-Gases?

  • Emission of F-gases (fluorinated gases) from refrigerants can be reduced through the introduction of substitutes with lower global warming potential. These include: HFCs with lower GWP, such as R32; hydrofluoroolefins (HFOs) and HFC-HFO blends. 16
  • Industrial users of F-gases can lower emissions by upgrading their gas recycling and destruction procedures, and replacing these gases with more environmentally friendly alternatives.

What Are The IPCC Targets For Greenhouse Gas Emissions?

How much greenhouse gas is safe? Unfortunately, no one knows for sure. Besides, given the ever-expanding global population, it is hard to predict the level of economic activity needed to sustain a reasonable standard of living within the world community.

In order to avoid catastrophic climate change, the IPCC state that global emissions of carbon dioxide must fall by about 45 percent (compared to 2010 levels), by 2030, and to “net-zero” by 2050. This should ensure that global warming does not exceed 1.5°C (above pre-industrial levels). A fall of 25 percent by 2030, and to “net zero” by 2075, would limit the rise to 2°C.

These “manageable” levels still spell disaster for many of the planet’s animals, life-forms and ecosystems. A rise of 2°C will extinguish 100 percent of the world’s coral reefs. A rise of 1.5°C will extinguish 90 percent.

What Are The Latest Figures For Greenhouse Gas Emissions?

The latest statistics on global emissions are as follows: total emissions for the year 2019 (the last full year before COVID-19) amounted to 59.1 GtCO2e (billion tons of CO2 equivalent). Of these, 38.0 GtCO2e came from fossil fuels and industry; 6.8 GtCO2e came from land use change; 9.8 GtCO2e came from man-made emissions of methane; 2.8 GtCO2e came from man-made nitrous oxide; 1.7 GtCO2e came from F-gases. (Note: like all figures on GHG emissions, these are approximate figures only.) 17

Global GHG emissions need to be approximately 45 percent lower in 2030 (compared to 2010 emissions), reducing to “net-zero” by 2050, in order to limit global warming to 1.5°C. 10

Unfortunately, fossil fuel combustion and greenhouse gas emissions are both still on an upward trajectory. 18 19 20 See also: Greenhouse Gas Statistics Lack Consistency.

What Are The Latest Figures For Methane?

Levels of methane (CH4) rose again last year (2018), continuing the surge of the past few years that scientists still can’t explain why methane levels are rising. Atmospheric concentrations of CH4 climbed by 10.77 parts per billion in 2018, the second highest increase in the past two decades, according to a report released recently by US agency NOAA. The problem is, that if methane levels keep climbing then the goals of the Paris Climate Agreement (2015) – of pegging global warming to 2°C and pursuing efforts to keep it below 1.5°C – will be very difficult to meet.

Keith Shine FRS, Regius Professor of Meteorology and Climate Science at the University of Reading, says about the rise in CH4: “the fact that growth rates in the atmospheric concentrations of methane are approaching the levels we saw in the 1980s, after a period of relatively slow growth, is deeply concerning. The fact that we don’t understand the reasons for this surge deepen that concern.”

Dr Rebecca Fisher of the Department of Earth Sciences at Royal Holloway University of London says: “We still do not know whether the growth is primarily an increase in natural emissions, such as from warmer or wetter wetlands, or increased anthropogenic emissions such as rice agriculture or fossil fuels.” 21 To find out the answer, see: Why Are Methane Levels Rising?

What Is The Emissions Gap?

For the last nine years, UN Environment have compiled an in-depth assessment of the latest scientific studies on current and future emissions of greenhouse gases.

Graph showing predicted global greenhouse gas emissions gap by 2030
Projected global greenhouse gas emissions gap in 2030. Report conclusion: “Unless global greenhouse gas emissions fall by 7.6 per cent each year between 2020 and 2030, the world will miss the opportunity to get on track towards the 1.5°C temperature goal of the Paris Agreement.” Source: UN Emissions Gap Report 2018.

It compares (a) the level of greenhouse gas emissions that the world can afford in order to maintain global temperatures within safe limits (1.5°C), with (b) the levels that are likely to be achieved in reality – based on the pledges made and actions taken by countries. The difference between the two sets of figures is known as the Emissions Gap – and right now it’s huge.

The U.N.’s 2020 Emissions Gap Report records the largest gap yet seen between where we are and where we need to be. It also cautions against expecting any long-term reduction in greenhouse gas emissions due to COVID-19 shutdowns. 22

Despite international efforts to resolve our climate crisis through ongoing UN Climate Talks & Timeline, there is a growing feeling that our climate plan can’t cope, and that a more stringent approach is needed.

Why is the Public So Complacent About Greenhouse Gas Levels?

With so many governments and organizations shouting about the unprecedented levels of greenhouse gases, and the climate dangers of using fossil fuels, why are people so complacent about climate change? Why aren’t they demanding more effective climate action?

One of the reasons for this complacency is the gradualism of warming. Greenhouse gases don’t destroy the planet overnight. So, people think everything is pretty much okay.

The trouble is, greenhouse gases linger in the atmosphere allowing concentrations to build up slowly and surely over time. Which not only causes the acceleration in warming that we are seeing today, but also makes the effects difficult to stop.

A large amount of CO2, for instance, is going to stay in the atmosphere and continue to warm the planet for thousands of years, even if all CO2 emissions cease tomorrow. Which means that the full consequences of our behavior may not become apparent until much later (say 2100), by which time it might be too late.

Another reason, is the continuing deceptions being promoted by the climate change denial machine, who claim there is genuine scientific doubt about wheter global warming exists. For details, see our article: What is Climate Change Denial?


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