Green House Effect
The solar radiation absorbed by a planet’s atmosphere will make the planet surface temperature rise. This is similar to the mechanism how a greenhouse help plants to keep warm. Hence it is named “Greenhouse Effect”. The atmosphere is like the glass of a greenhouse, helping Earth to preserve a certain amount of heat. Otherwise, Earth would be too cold to live on.
Without greenhouse effect, the average temperature of Earth’s surface would be only -18°C. The greenhouse effect is credit for maintaining the Earth’s reasonable average temperature at 15°C. However, human activities have produced too much greenhouse gas, causing the temperature to keep increasing.
Green House Gases
Greenhouse gases in the atmosphere can capture sunlight reflected from the surface and convert it into heat. That is the key factor to help Earth maintain a certain temperature. They are originally a natural mechanism to protect Earth. There are many different greenhouse gases, and the three main ones are carbon dioxide, methane and nitrous oxide.
Based on the Global Warming Potential (GWP) of carbon dioxide, methane is 72 and nitrous oxide is 298 times stronger. In the long run, the GWP of carbon dioxide is not easy to decrease, while methane decreases faster and nitrous oxide decreases slower. This is because carbon dioxide structure is strongly linked and difficult to combine with other atoms to form new elements. It lasts for more than a thousand years. However, methane is more reactive and has a shorter life span.
Therefore, reducing the amount of methane in the atmosphere is the key to curbing global warming.
About Methane
Methane is the most dangerous of these three gases. It is also the main ingredient of natural gas, a common fuel that people use. Methane was once in large quantities in the primordial atmosphere when Earth was just formed. After billions of years of environmental evolution, the Earth’s temperature gradually dropped, and it was slowly fixed in the ground and under the sea. In the polar regions, it was frozen under the permafrost. Besides natural reserves, methane is also created in many conditions. Such as biogas produced in anaerobic decomposition, digestion process of animals (ex. cattle), and bacterial actions.
In 1953, the classic experiments of Harold Urey and Stanley Miller discovered the origin of lives. A mixture of methane, ammonia, hydrogen, and water turned into many organic compounds when charged. The essential ingredients for life — amino acids, was also included. This is why animals emit methane, because it is one of the components of animal’s body.
Methane is colorless and odorless under normal temperature and pressure. But it can be easily ignited or exploded when the content in the air rises to only 4.4-17%. If the temperature is too high, the permafrost layer and the Earth’s crust will melt or become unstable for methane to be fixed. If methane is mass released, the consequences will be disastrous. And methane is now gradually released into the atmosphere because ocean temperature rises and permafrost melts due to global warming. The most dangerous domino is tilting.
All animals produce greenhouse gases. Besides the original population and animals on Earth, additional livestock in large numbers will cause a dramatic increase in greenhouse gases. The report of United Nations Food and Agriculture Organization (FAO) in 2006 states that (P.112-114) livestock activities account for 18% of global anthropogenic greenhouse gas emissions. This is a higher share than 13%, the total of all transportation.
Sources of Three Main GHG
The sources of three main greenhouse gases are:
Carbon Dioxide: The livestock sector accounts for 9% of global anthropogenic CO2 emissions. The largest share of this derives from land-use changes. Especially deforestation for expansion of pastures and feed-crops.
Methane: The livestock sector accounts for 37% of global anthropogenic CH4 emissions. Most of that is from enteric fermentation by ruminants.
Nitrous Dioxide: The livestock sector accounts for 65% of global anthropogenic N2O emissions. The great majority is from manure.
About Different Data
When looking up greenhouse gases, a variety of different data will be found. If they are quoted from FAO, the data comes mainly from two reports: Livestock’s Long Shadow in 2006 and Tackling Climate Change Through Livestock in 2013. The data in these two reports are both cited from IPCC statistics. The reason for the difference is that the reference period varies.
The total anthropogenic GHG emission in Livestock’s Long Shadow used a 2001 to 2004 reference period. The calculated emission percentages are: CO2 shared 9%, CH4 shared 37%, N2O shared 65%. The total anthropogenic GHG emission in Tackling Climate Change through Livestock used a 2005 reference period and calculated CO2 shared 14.5%, CH4 shared 44%, N2O shared 53%. Whichever report it is, given the current number and scale of livestock farming, greenhouse gas emissions are bound to far exceed these figures.
How many times the global warming potential (GWP) of methane is stronger than carbon dioxide over a 20-year period differ. It is because of different values estimated by different research organizations. It ranges from 70 to 85. This book uses the value estimated by IPCC in 2007, which is 72.
Further Reading: 1-4 How Many Animals Are Slaughtered Worldwide Every Year? ｜ 1-5 The Real Percentage of Emission
Cited Reports: Livestock’s Long Shadow ｜ Tackling Climate Change through Livestock
Relative Download: Diet and Environment Relative Download
