main natural sources greenhouse - itesm...greenhouse gases •the global warming potential (gwp)...

Main Natural Sources of Greenhouse Gases

Content

• Atmospheric Composition• Composition of the Earth’s Atmosphere• Greenhouse Gases• The Radiative‐Forcing bar chart: AR5 version• Natural Greenhouse Gases

• Water Vapor and Clouds• Carbon dioxide (CO2)• Methane (CH4)• Nitrous oxide (N2O)• Tropospheric Ozone (O3)• Halogen‐Containing Gases

Atmospheric Composition

• The main constituents of the dry atmosphere are nitrogen (78.084% by volume), oxygen (20.946% by volume) and argon (0.934% by volume), but much lower concentrations other noble gases can also be found.

• Concentrations of these gases do not vary substantially in time and space (in the lower 80 km layer of the atmosphere) and therefore they are called permanent gases.

Composition of the Earth’s Atmosphere

Greenhouse Gases

• A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range.

• This process is the fundamental cause of the greenhouse effect.• The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.

Greenhouse Gases

• When ranked by their direct contribution to the greenhouse effect, the most important are:

Compound Formula Contribution(%)

Water vapor and clouds H2O 36 – 72%

Carbon dioxide CO2 9 – 26%

Methane CH4 4–9%

Ozone O3 3–7%

Greenhouse Gases

• The global warming potential (GWP) depends on both the efficiency of the molecule as a greenhouse gas and its atmospheric lifetime.

• GWP is measured relative to the same mass of CO2 and evaluated for a specific timescale.

• Thus, if a gas has a high (positive) radiative forcing but also a short lifetime, it will have a large GWP on a 20‐year scale but a small one on a 100‐year scale.

• Conversely, if a molecule has a longer atmospheric lifetime than CO2its GWP will increase with the timescale considered.

• Carbon dioxide is defined to have a GWP of 1 over all time periods.

http://en.wikipedia.org/wiki/Greenhouse_gas

Climate Change 2013: IPCC AR5 WG1 SPM, Fig. SPM ‐05

The Radiative‐Forcing bar chart: AR5 version

Natural Greenhouse Gases

• The Natural Greenhouse Gases are:• Water Vapor and Clouds• Carbon dioxide (CO2)• Methane (CH4)• Nitrous oxide (N2O)• Tropospheric Ozone (O3)• Halogen‐Containing Gases

Water Vapor and Clouds

• The most important and most abundant atmospheric greenhouse gas is water vapor.

• Human sources have only a small direct influence on tropospheric water vapor concentrations, because they are largely controlled by local temperatures.

• The water vapor concentration can be several percent over warm tropical seas and very low over frigid ice fields at the poles.

• As planetary warming occurs, water vapor concentration increases and adds to the warming effect.

Natural Sources of Carbon Dioxide (CO2)

• The natural sources of carbon dioxide (CO2) are:• decomposition, ocean release, respiration and volcanoes.

• 42.8 percent of all naturally produced CO2emissions come from ocean‐atmosphere exchange.

• Other important natural CO2 sources include plant and animal respiration (28.56%) as well as soil respiration and decomposition (28.56%).

• A minor amount is also created by volcanic eruptions (0.03%).

http://whatsyourimpact.org/greenhouse‐gas‐sources


Ocean‐atmosphere exchange• The largest natural source of carbon dioxide emissions is from ocean‐atmosphere exchange. This produces 42.84% of natural carbon dioxide emissions. The oceans contain dissolved carbon dioxide, which is released into the air at the sea surface. Annually this process creates about 330 billion tons of carbon dioxide emissions.

• Many molecules move between the ocean and the atmosphere through the process of diffusion, carbon dioxide is one of them. This movement is in both directions, so the oceans release carbon dioxide but they also absorb it. The effects of this movement can be seen quite easily, when water is left to sit in a glass for long enough, gases will be released and create air bubbles. Carbon dioxide is amongst the gases that are in the air bubbles.



Plant and animal respiration• An important natural source of carbon dioxide is plant and animal respiration, which accounts for 28.56% of natural emissions. Carbon dioxide is a byproduct of the chemical reaction that plants and animals use to produce the energy they need. Annually this process creates about 220 billion tons of carbon dioxide emissions.

• Plants and animals use respiration to produce energy, which is used to fuel basic activities like movement and growth. The process uses oxygen to break down nutrients like sugars, proteins and fats. This releases energy that can be used by the organism but also creates water and carbon dioxide as byproducts.



Soil respiration and decomposition• Another important natural source of carbon dioxide is soil respiration and decomposition, which accounts for 28.56% of natural emissions. Many organisms that live in the Earth's soil use respiration to produce energy. Amongst them are decomposers who break down dead organic material. Both of these processes releases carbon dioxide as a byproduct. Annually these soil organisms create about 220 billion tons of carbon dioxide emissions.

• Any respiration that occurs below‐ground is considered soil respiration. Plant roots, bacteria, fungi and soil animals use respiration to create the energy they need to survive but this also produces carbon dioxide. Decomposers that work underground breaking down organic matter (like dead trees, leaves and animals) are also included in this. Carbon dioxide is regularly released during decomposition.



Volcanic eruptions• A minor amount carbon dioxide is created by volcanic eruptions, which accounts for 0.03% of natural emissions. Volcanic eruptions release magma, ash, dust and gases from deep below the Earth's surface. One of the gases released is carbon dioxide. Annually this process creates about 0.15 to 0.26 billion tons of carbon dioxide emissions.

• The most common volcanic gases are water vapor, carbon dioxide, and sulfur dioxide. Volcanic activity will cause magma to absorb these gases, while passing through the Earth's mantle and crust. During eruptions, the gases are then released into the atmosphere.


Natural Sources of Methane (CH4)

• The main natural sources include wetlands, termites and the oceans.

• 78% of natural CH4 emissions are produced by wetlands.

• Other natural CH4 sources include termites (12%) and the oceans (10%).



Wetlands.• Wetlands are the largest natural source of methane. This produces 78% of natural methane emissions. The water‐logged conditions of wetlands are perfect for microbes who require environments with no oxygen and abundant organic matter.

• While part of wetland related emissions is absorbed by methane‐consuming microbes, a large percentage escapes into the atmosphere. Wetlands create 147 million tons of methane each year.



Termites.• Termites are a significant natural source of methane. During the normal digestion process of a termite, methane is produced. Termites eat cellulose but rely on micro‐organisms in their gut to digest it which produces methane during the process. This is responsible for 12% of natural methane emissions.

• Each termite produces very small amounts of methane on a daily basis. However, when this is multiplied by the world population of termites, their emissions add up to 23 million tons of methane annually.



Oceans.• Another significant natural source of methane comes from the oceans. Methane producing microbes living in the ocean create these emissions. This creates 10% of natural methane emissions. Globally, oceans create 19 million tons of methane annually.

• The majority of oceanic methane emissions gets produced in deeper sediment layers of productive coastal areas. This accounts for 75% of the oceans methane emissions. The methane created by these microbes mixes with the surrounding water and is emitted to the atmosphere from the ocean surface.


Natural Sources of Nitrous Oxide (N2O)

• The main natural sources are soils under natural vegetation and the oceans.

• 60% of natural N2O emissions are produced by soils under natural vegetation.

• Other natural sources include the oceans (35%) and atmospheric chemical reactions (5%)



Soils under natural vegetation.• The largest natural source of nitrous oxide is from soils under natural vegetation. This produces 60% of natural emissions. Uncultivated soils make up the majority of the Earth's land surface. So the nitrous oxide produced by microbes that break down nitrogen in these soils are considered natural sources.

• Riparian and tropical rainforest soils are important contributors to this source because they have higher nutrient availability and moisture levels. This facilitates microbial nitrification and denitrification. Soils under natural vegetation create 6.6 million tons of nitrous oxide each year.



Oceans.• An important natural source of nitrous oxide emissions comes from the oceans. Nitrous oxide producing microbes living in the ocean create these emissions. This produces 35% of natural emissions which equals 3.8 million tons of nitrous oxide annually.

• Much of the nitrous oxide in the oceans arises from microbial activity in and around sinking particles, such as fecal pellets. These particles provide the anaerobic conditions necessary for denitrification, a process which creates nitrous oxide as a by‐product.



Atmospheric chemical reactions.• Chemical reactions in the atmosphere produce a significant amount of nitrous oxide emissions. The atmosphere acts as a source for nitrous oxide through the oxidation of ammonia which is responsible for 5% of emissions.

• Ammonia is a natural occurring gas in the atmosphere. The oceans, manure from wild animals as well as aging and rotting plants form the most important natural sources of ammonia in the air. The oxidization of ammonia from natural sources creates 600,000 tons of nitrous oxide annually.


Natural Sources of Tropospheric Ozone (O3)

• Gases, such as CO and CH4, which are emitted by natural biological processes and human activities, can react in sunlight to form O3 in the troposphere.

• Tropospheric O3 only lasts for a few days or weeks in the atmosphere, so its distributions are variable.

Natural Sources of Halogen‐Containing Gases

• Almost all of the long‐lived halogen‐containing gases in the atmosphere are synthetic and did not exist in the atmosphere before the industrial era.

• Only a few such gases, for example, methyl bromide, methyl chloride, and tetrafluoromethane (CF4), occur naturally.

Main Natural Sources of Greenhouse Gases

main natural sources greenhouse - itesm...greenhouse gases •the global warming potential (gwp)...

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