The global mean temperature has increased since 1750, which has been designated as the start of the industrial revolution. The mean global temperature has increased about 1.2̊C (2.16̊F). Atmospheric carbon dioxide has increased from 280 ppm to 412 ppm over a 270 year period.
Global warming is caused by the increased emissions of greenhouse gases into the atmosphere that are byproducts from increased burning of fossil fuels. The three primary greenhouse gases are carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O).
Energy from the sun drives the earth’s climate. The sun radiates energy at very short wavelengths at the visible and near visible (ultraviolet) part of the electromagnetic spectrum. The solar energy reaching the earth’s atmosphere that is facing the sun is about 1,365 Watts/m2 with greater amounts at the equator than at the north and south latitudes.
About 20% of this energy is reflected back to space by clouds and small aerosol particles, and about 10% of this energy is reflected by the earth’s cryosphere, the ice, snow, and glaciers. Collectively, this high reflectivity is called the earth’s albedo.
The suns energy not reflected back to space is absorbed by the atmosphere at about 78 W/m2 of latent heat, and is absorbed by the earth’s surface as heat at about 168 to 240 W/m2.
In order to balance the incoming solar radiation, the earth emits the same amount of energy as outgoing longwave radiation. If all of this longwave energy were permitted to escape into space, the average global temperature of the earth would be -19̊ C (-2.2̊ F) and all water would be frozen and no life could exist.
Fortunately, the earth is protected by a partial blanket known as the natural greenhouse effect made up of atmospheric water vapor as clouds and carbon dioxide that absorbs and reradiates some of the earth’s longwave radiation back to the earth resulting in a normal average earth temperature of around 14̊ C (57 ̊ F) in which some water is liquid and life as we know can exist.
These complex interactions of the earth’s systems maintained a stable global temperature for 10,000 years before the industrial revolution.
The activities of the industrial revolution disrupted the earth’s stable conditions causing increasing greenhouse gas emissions and a rising global temperature.
A substantial increase in terrestrial soil sequestration of atmospheric carbon dioxide can be as effective at reducing the rate of global warming as the primary objective to reduce emissions of carbon dioxide from fossil fuel burning.
Long term persistence of carbon storage in soils by the most promising biogeochemical processes requires a large active microorganism biomass, which strongly suggests the direction for the improved land management practices.
Terrestrial soils have stored a huge quantity of carbon at a level of 1.56 trillion tons SOC to a 1 meter depth. The terrestrial soil carbon storage is large and has been increasing because the increase of atmospheric carbon dioxide has increased terrestrial plant photosynthetic rates and plant growth biomass.
During the eighteen year period of 1990 to 2007, terrestrial soil carbon storage increased at a rate of 2.76 billion tons C/yr. During the eleven year period of 2007 to 2017, terrestrial soil carbon storage increased at a rate of 3.98 billion tons C/yr. These increases in soil carbon storage mean that, with the CO2 effect, terrestrial soils are removing CO2 from the atmosphere at a rate equivalent to all of the CO2 emissions from the soils plus about 33.7% of the CO2 emissions from all the fossil fuel burning per year.
This is the reason, the rate of global warming is increasing at a rate slower than expected.
The carbon storage in the oceans is important but has not changed much. During 1990 to 2007, oceanic carbon storage was at 2.54 billion tons C/yr. During 2007 to 2017, oceanic carbon storage was at 2.6 billion tons C/yr.
The total annual anthropogenic (human caused) carbon dioxide emissions increased during the decade of 2007 to 2017 compared to an earlier 18 year period of 1990 to 2007.
During 2007 to 2017, total annual carbon dioxide emissions were 11.77 billion tons/yr, an increase of 9.0%, emissions from fossil fuel burning increased 35.4%, from cement production increased 37.1%, and from tropical deforestation decreased 54.1% compared to the earlier period.
The quantity of atmospheric carbon dioxide increased by 5.19 billion tons/yr which was only 44.1% of the total annual carbon dioxide emissions.
The annual rate of carbon dioxide emissions added to the atmosphere did not increase as much as expected because the annual amount of carbon dioxide that was moved into terrestrial soils increased 44.4% compared to the earlier period as a result of the CO2 effect that increased plant photosynthesis.
Methane (CH4) emissions are produced by methanogenesis when decomposition of organic matter occurs under anaerobic conditions (without oxygen) in waterlogged soils. The total methane production in the world is at 160 million tons/yr, with 101 million tons/yr from natural wetlands and peatlands and 58 million tons/yr from rice fields. Some additional methane is emitted from landfills, biomass burning, and domestic sewage. Methane has an atmospheric residence time of about 10 years. In the atmosphere, methane is eliminated by reacting with hydroxyl radicals (OH).
Nitrous oxide (N2O) emissions are produced by industrial fossil fuel burning and biomass burning at about 13 million tons/yr and from agricultural cropland emissions at just over 4.4 million tons/yr caused by application of greater quantities of nitrogen fertilizer than needed by the plants. The total atmospheric nitrous oxide emissions are at about 17.6 million tons/yr for the world.
The worlds forest soils plus the wood in long lived trees hold about 774 billion tons of SOC which is about 49.6% of the worlds sequestered carbon. Forests occupy around 27.7% of the worlds land area.
The development of agriculture has permitted the development of an advanced human civilization. Increases in the amount of cropland to 12.6% the worlds land area required the conversion of natural forest and grassland ecosystems which has caused great losses of stored soil carbon at quantities of 44 to 99 billion tons of SOC.
The rate of re-carbonization of agricultural managed cropland is slow. Collectively, all cropland soils to 1 meter depth hold only 177 billion tons of SOC which is about 11.3% of the worlds sequestered carbon.
Pasturelands occupy around 23.8% of the worlds land area. Pastureland soils hold 484 billion tons of SOC to 1 meter depth which is about 31.0% of the worlds sequestered carbon.
Carbon dioxide, methane, and nitrous oxide emissions are still being added to the earth’s atmosphere and the climate is still warming, albeit, at a slower rate then expected.
The worlds forestlands are removing about as much carbon dioxide as they can.
However, the worlds cropland and pastureland soils have the potential to remove much more atmospheric carbon dioxide than they are at the present.
Agricultural producers should manage their cropland and pastureland to capture the greatest quantity of carbon dioxide by using the best management practices that can be implemented in order to assist the agricultural industry in saving the world during this global warming crisis.
