Top Three Greenhouse Gases on Earth

Top Three Greenhouse Gases on Earth
Sketch of Greenhouse Effect on Earth courtesy of A Loose Necktie under CC BY-SA 4.0

Top three greenhouse gases include carbon dioxide and methane. Water vapor (H2O – see above cartoon sketch) is a major greenhouse gas NOT usually mentioned in newscasts and radio news spots on global warming. It is often overlooked! Water vapor is one of the three major greenhouse gases in Earth’s atmosphere; carbon dioxide and methane are the other two. In this post, we review Earth’s top three greenhouse gases that contribute to Earth’s global warming. To reduce global warming, we make suggestions that you, an Earthling, can take.

Dr. MMM of AstroPicionary has taught astronomy to 10,000+ students over 15+ years at a USA Carnegie Level R1 University. Dr. MMM continues to teach astronomy and physics. She authors textbooks in astronomy that are in use worldwide. Here, Dr. MMM discusses a hot topic in today’s news – greenhouse effect, greenhouse gases, and global warming. Her goal here is to help put water vapor back in the top three list of major greenhouse gases. Another goal is to determine whether water vapor emissions by humans is a major contributor to global warming.

Greenhouse Effect – What Is It?

The cartoon sketch above depicts the greenhouse effect on Earth: Sunlight (yellow wavy lines) enters Earth’s atmosphere, and infrared radiation (upward pointing orange wavy lines) tries to leave Earth’s atmosphere. Molecules within Earth’s atmosphere prevent some infrared radiation from leaving: This blocking reflects infrared radiation downward to Earth’s surface (downward pointing orange wavy lines), warming the atmosphere. This warming is a consequence of the greenhouse effect.

The AstroPictionary YouTube video below explains the term greenhouse effect for any star and atmosphere of a celestial body. The video uses Sun and Earth as an example.

Video on greenhouse effect in AstroPictionary YouTube Channel

Greenhouse effect is good for planet Earth. It keeps Earth’s lower atmosphere warm.

Can you imagine if Earth did not have this greenhouse effect? Earth’s global temperature would be around -20 oC or –4 oF. Brrrrr, days would be cold everywhere on Earth; nights would be even colder! The sketch below depicts what frozen Earth might look like.

Cartoon of a frozen Earth courtesy of Kevin M. Gill under CC BY 2.0

Greenhouse Gases (GHGs)

The sketch at the top of this post lists three chemical compounds that are in Earth’s atmosphere: H2O, CO2, and CH3. H2O is the chemical compound for water vapor; CO2 is the chemical compound carbon dioxide; CH3 is the chemical compound for methane. Water vapor, carbon dioxide, and methane are the top three greenhouse gases (GHG) in Earth’s atmosphere. Of these three, water vapor is most abundant. Carbon dioxide is second, and methane is third most abundant. Let’s look at each of these.

Water Vapor

One GHG in Earth’s atmosphere is water vapor. Let’s look Earth’s water cycle to see how water vapor is put into Earth’s atmosphere.

The diagram below shows Earth’s water cycle: Heat from the Sun causes water vapor to evaporate from oceans, seas, rivers, etc. Plants absorb water; after some time, they transpire water vapor into the atmosphere. Of evaporation and transpiration, water transpiration contributes the least amount, only about 10%.

Diagram of water cycle courtesy of Ehud Tal under CC BY-SA 4.0

The next step in the cycle is condensation: Water vapor condenses onto particles; particles include floating dust and sea salt. Accumulation of water droplets forms into clouds in Earth’s atmosphere; keep in mind that not all water vapor in Earth’s atmosphere forms into clouds.

The next step in the cycle is returning water to Earth: Clouds can produce rain, ice, or snow. The water cycle starts anew.

Water vapor contributes about 50% towards Earth’s GHGs. It is the single largest component to Earth’s GHGs.

Water vapor is a condensing GHG. Methane and carbon dioxide are non-condensing GHGs. Let’s look at methane next.


Graphic of methane cycle courtesy of The Global Carbon Project under CC BY 4.0

As shown in the above graphic, methane is in Earth’s atmosphere. Methane comes from several sources. These sources include fossil fuels, agriculture, waste, bio burns, wetlands, and natural emissions. Let’s look at each of these sources.

  • Fossil fuels include wood, coal, gas. Extraction processes release methane to the atmosphere. Natural gas, a fossil fuel, has methane as its primary component.
  • Agriculture includes cattle, goats, and sheep. Digestion in stomachs of agriculture releases methane. Digestion in stomachs of camels, buffalo, and termites too releases methane inside the animal’s body. Exhaling and belching releases this methane to the atmosphere.
  • Waste is in landfills. Decomposing organic waste releases methane.
  • Biomass is material that has a plant-base. Examples include woodlands and savanna. Biofuel is biomass burning to generate heat and electricity. Examples of biomass biofuel include agricultural waste and peat moss.
  • Wetlands include water soaked rice paddy fields. Wetlands have microbes, which produce methane via anaerobic respiration.
  • Natural emissions of methane include permafrost melting; decomposition of wild vegetation; and aeration from lakes, wetlands, seas, and oceans. Aeration is a mixing of air and water, which naturally removes methane from wetlands, lakes and oceans.

Of these sources to methane in Earth’s atmosphere, fossil fuels, agriculture, waste, and some bio burns have human influences. Aeration from wetlands, naturally occurring fires, and emissions from nature are examples of natural sources of methane into Earth’s atmosphere.

Carbon Dioxide

Carbon dioxide is a third GHG in Earth’s atmosphere. Like water, carbon dioxide has a cycle. This cycle is depicted in the graphic below.

Photosynthesis; plant respiration; microbial respiration and decomposition; and fossil fuel burning are sources to CO2 emission into Earth’s atmosphere from land. Aeration from a mixing of air and sea is a source of CO2 emission from water.

Removal of carbon dioxide from Earth’s atmosphere is from plant absorption and soils on land. Removal from water is from air-sea gas exchange.

Graphic of carbon dioxide cycle courtesy of US Government under Public Domain

The carbon dioxide cycle naturally puts carbon dioxide into Earth’s atmosphere and naturally takes carbon dioxide out. Human influences contribute to emissions. Human influences include fossil fuel burning for electricity and transportation and in manufacturing of cement.

Water Vapor – An Ignored Greenhouse Gas?

Pie chart of greenhouse gas emissions courtesy of EPA IPCC under Public Domain

Water vapor, carbon dioxide, and methane are the three largest sources of greenhouse gases in Earth’s atmosphere. These are not the only sources; nitrous oxide and Fluorinated (F) gases are others.

The pie chart at left shows the percentages of these gases emitted globally into Earth’s atmosphere. Carbon dioxide occupies most of the pie followed by methane, nitrous oxide, and F-gases. Notice that carbon dioxide is broken into fossil fuel and industrial processes and other land use.

Often charts like this one do not list water vapor. Humans do contribute to water vapor in Earth’s atmosphere via activities like boiling water. Yet, charts like these do not list water vapor emission.

A reason why water vapor is not listed on charts may be location. Water vapor emission by human activity is to Earth’s lower atmosphere. Water vapor importance as a greenhouse gas is in Earth’s upper atmosphere. An increase in water vapor to Earth’s lower atmosphere does not result in much increase heating of Earth’s atmosphere. Human activity in producing water vapor does not contribute much to global warming.

Actions To Minimize GHG Emissions

Here’s the bad news: Methane is a much stronger GHG. Carbon dioxide is not as strong of a GHG. The good news is that methane does not live very long in Earth’s atmosphere, only about 12 years; carbon dioxide lives much longer. Other good news is that methane is easy to remove from Earth’s atmosphere: Methane naturally breaks down in Earth’s atmosphere over about a decade. Carbon dioxide does not break down as easily in this same amount of time. As such, reducing methane production is the fastest way to reduce global warming.

Humans can do their part to minimize methane emissions:

  • Humans can reduce the amount of cow, goat, sheep, and buffalo meat intake. By reducing, agriculture quantities lower, thereby lower methane emissions.
  • Humans can reduce the amount of fossil fuels burned; turning to solar or wind or other non-fossil energy production reduces amounts of methane emissions.
  • Humans can reduce organic waste for landfills; reducing waste minimizes methane emissions.

These are just a few activities Earthlings can do to help reduce global warming. Why not try one to do your part!

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About the author

Michele M. Montgomery earned a B.S. Degree in Nuclear/Mechanical Engineering from the Pennsylvania State University, an M.S. Degree in Physics from The University of Alabama with a concentration in Solar Physics, and a Ph.D Degree in Physics from Florida Institute of Technology with a concentration in close binary star systems. She joined the faculty at The University of Central Florida Physics Department in 2004 where she regularly taught astronomy, astrophysics, and cosmology. In 2006, she noticed that a large, urban college nearby to UCF did not teach astronomy at one of their largest campuses. She began teaching astronomy at this East Campus of Valencia College, a college that has more than 60,000 students; she still teaches four courses of astronomy each fall, spring, and summer semesters. The astronomy program atValencia College East has grown significantly with several more faculty added who teach astronomy.

By 2019, Dr. Montgomery has taught astronomy to more than 10,000 college and university students, both online and face-to-face. Many of her students have gone on to take her astrobiology, astrophysics, and space physics courses. 

By 2016, Dr. Montgomery had co-authored several astronomy texts and quiz/exam banks. Her work appears in several domestic and international astronomy text books (e.g., Horizons by Cengage, Universe by Cengage, Foundations of Astronomy by Cengage) that are used both at the higher education as well as at the high school levels. Starting in Fall 2019, Dr. Montgomery switched gears to authoring digital textbooks and research full time, while still teaching 12 courses of astronomy and up to eight conceptual, algebra, and/or calculus-based physics courses each year. Her research interests are numerical simulations using Smoothed Particle Hydrodynamics of close binary star systems. She also regularly is granted telescope time on the NASA's Kepler space telescope for observing eclipsing binary star systems. She has also observed using Gemini South, Keck, and Kitt Peak ground-based telescopes. Her major teaching areas are Astronomy, Astrobiology, Astrophysics, Cosmology, Space Weather/Space Physics.