The main greenhouse gases linked to climate change are 1) carbon dioxide (72 percent ); 2) methane (18 percent); 3) nitrous oxide (9 percent); other gases (1 percent).

Nitrous oxide has been called the worst greenhouse gas. On top of that it also slowly depletes the ozone layer. Better known as laughing gas, nitrous oxide is 296 times more powerful from a global warming perspective than carbon dioxide and has recently replaced chlorofluorocarbons (CFCs) as the primary cause of ozone depletion. About a third of the world’s nitrous oxide emission are caused by human activities, including the use of fertilizer, fossil fuels, livestock manure and industry. One of the primary methane sources is manure from dairy cows, cattle and other animals. The other two thirds come from nature, mostly releases from soil bacteria. A study by the U.S. National Oceanic and Atmospheric Administration published in Science in September 2009, called nitrous oxide emission “the single most important ozone-depleting substance emission and is expect to remain the largest throughout the century.”

HFC23, a hydroflurocarbon, is greenhouse gas whose impact on global warming is 11,700 times greater than that of carbon dioxide.

Carbon Dioxide and Climate Change

Carbon dioxide is a greenhouse gas because it absorbs and radiates heat. Warmed by sunlight, Earth’s land and ocean surfaces continuously radiate thermal infrared energy (heat). Unlike oxygen or nitrogen (which make up most of our atmosphere), greenhouse gases absorb that heat and release it gradually over time, like bricks in a fireplace after the fire goes out. Without this natural greenhouse effect, Earth’s average annual temperature would be below freezing instead of close to 60°F. But increases in greenhouse gases have tipped the Earth's energy budget out of balance, trapping additional heat and raising Earth's average temperature. [Source: NOAA]

Carbon dioxide is the most important of Earth’s long-lived greenhouse gases. It absorbs less heat per molecule than the greenhouse gases methane or nitrous oxide, but it’s more abundant, and it stays in the atmosphere much longer. Increases in atmospheric carbon dioxide are responsible for about two-thirds of the total energy imbalance that is causing Earth's temperature to rise.

Another reason carbon dioxide is important in the Earth system is that it dissolves into the ocean like the fizz in a can of soda. It reacts with water molecules, producing carbonic acid and lowering the ocean's pH (raising its acidity). Since the start of the Industrial Revolution, the pH of the ocean's surface waters has dropped from 8.21 to 8.10. This drop in pH is called ocean acidification.

A drop of 0.1 may not seem like a lot, but the pH scale is logarithmic; a 1-unit drop in pH means a tenfold increase in acidity. A change of 0.1 means a roughly 30% increase in acidity. Increasing acidity interferes with the ability of marine life to extract calcium from the water to build their shells and skeletons

Carbon Dioxide Levels Hit New High in 2021

NOAA said carbon dioxide levels in the atmosphere increased to 2.66 parts per million in 2021 over 2020, one of the higher increases in history but not a record. The annual average for 2021 for carbon dioxide was 414.7 parts per million. Pre-industrial is about 280 parts per million. NOAA said carbon dioxide are now the highest since about 4.3 millions year when the sea level was about 75 feet (23 meters) higher and the average temperature was about 7 degrees Fahrenheit (3.9 degrees Celsius) warmer. [Source: Seth Borenstein, Associated Press, April 8, 2022]

Carbon dioxide levels in the air peaked in May 2021 to a new all time high, and amount nearly 50 percent higher than when the industrial age began and they are growing at a record fast rate. Associated Press reported: The National Oceanic and Atmospheric Administration said the average carbon dioxide level for May was 419.13 parts per million. That’s 1.82 parts per million higher than May 2020 and 50 percent higher than the stable pre-industrial levels of 280 parts per million, said NOAA climate scientist Pieter Tans. [Source: Seth Borenstein, Associated Press, June 8, 2021

“Carbon dioxide levels peak every May just before plant life in the Northern Hemisphere blossoms, sucking some of that carbon out of the atmosphere and into flowers, leaves, seeds and stems. The reprieve is temporary, though, because emissions of carbon dioxide from burning coal, oil and natural gas for transportation and electricity far exceed what plants can take in, pushing greenhouse gas levels to new records every year.

“Reaching 50 percent higher carbon dioxide than preindustrial is really setting a new benchmark and not in a good way,” said Cornell University climate scientist Natalie Mahowald, who wasn’t part of the research. “If we want to avoid the worst consequences of climate change, we need to work much harder to cut carbon dioxide emissions and right away.”

The one-year jump in carbon dioxide was not a record, mainly because of a La Nina weather pattern, when parts of the Pacific temporarily cool, said Scripps Institution of Oceanography geochemist Ralph Keeling. Keeling’s father started the monitoring of carbon dioxide on top of the Hawaiian mountain Mauna Loa in 1958, and he has continued the work of charting the now famous Keeling Curve. Scripps, which calculates the numbers slightly differently based on time and averaging, said the peak in May was 418.9.

Pandemic lockdowns slowed transportation, travel and other activity by about 7 percent, earlier studies show. But that was too small to make a significant difference. Carbon dioxide can stay in the air for 1,000 years or more, so year-to-year changes in emissions don’t register much. The 10-year average rate of increase also set a record, now up to 2.4 parts per million per year.

“Carbon dioxide going up in a few decades like that is extremely unusual,” Tans said. “For example, when the Earth climbed out of the last ice age, carbon dioxide increased by about 80 parts per million and it took the Earth system, the natural system, 6,000 years. We have a much larger increase in the last few decades.” By comparison, it has taken only 42 years, from 1979 to 2021, to increase carbon dioxide by that same amount.

Sources of Carbon Dioxide and Greenhouse Gases

About half the carbon dioxide released into the atmosphere comes from natural sources and half from human causes. The main man-made contributor to the greenhouse affect in the world today is the burning of fossil fuels such as coal and oil by vehicles and factories.

According to NASA, human activities such as burning of coal and other fossil fuels, cement production and deforestation have increased the atmospheric carbon dioxide concentration by 47 percent since the Industrial Revolution started as of 2021. Energy-related and industrial activities accounting for 60 percent of human-caused greenhouse gas discharges worldwide. In the 2000s, about 80 percent of the increase in man-made carbon dioxide is attributed to the burning of fossil fuels, with 60 percent of that coming from industrialized nations. The United States produced 5.8 billion metric tons of carbon dioxide in 2003 alone, most of it from cars and coal-fired power plants. Large amounts are also spewed out of factories and oil and gas rigs.

Agriculture and forestry account for 30 percent of greenhouse gases. Plowing releases carbon dioxide. Rice fields are another major source. Cattle, sheep and pigs belching and excreting methane are another major source of greenhouse gases. The remaining 20 percent comes mainly from deforestation. The burning of forests adds carbon dioxide to the atmosphere. The absence of trees prevents them from soaking up carbo dioxide and producing oxygen. Grassland soil and plants store large amounts of carbon dioxide. When they are burned they release large amounts of carbon dioxide into the atmosphere and contribute to global warming.

Other contributors include leaky pipelines, which release natural gas, and depletion of sea life, which can absorbs carbon dioxide. Carbon dioxide can remain in the ocean for 100 years or more before it is recycled or it can be recycled right away. Jet travel is the fastest-growing source of greenhouse gases. Aircraft release more than 6000 million tons of carbon dioxide into the atmosphere every year, accounting for 3.5 percent of global warming. Compared to driving the same distance, a short haul flight generates 21 percent more carbon dioxide per passenger.

Emissions of greenhouse gases by industry are declining. The main sources of emission increases are power plants and vehicles. Of particular concern are the large number of coal-fired power plants in China, the United States and India and increases in the number of vehicles in China, India and the developing world.

Methane and Climate Change

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fuels and energy
Methane is a greenhouse gas and a major cause of climate change. A compound of carbon and hydrogen, which makes it exceptionally good at trapping heat, it is released from both natural sources, such as wetlands and termites, and also through human activities such as agriculture, fossil fuel exploitation and landfill sites. Livestock farming is a major source of methane emissions. Methane is a natural gas increasingly used energy source. Scientists also fear future release of trapped methane under the ocean and in frozen Arctic land, but there's no indication that's happening on a large scale. [Source: Matt McGrath, BBC, November 1, 2021]

Methane is a big contributor to climate change, leading to about a 0.9 degrees Fahrenheit (0.5 degrees Celsius) increase in temperature since the 19th century, according to the Intergovernmental Panel on Climate Change. Carbon dioxide has caused about 50% more warming than methane. Methane is about 25 times more powerful at trapping heat than carbon dioxide. But it only lasts nine years in the air instead of thousands of years like carbon dioxide. [Source: Seth Borenstein, Associated Press, April 8, 2022]

Associated Press reported: Because it doesn’t last in the air long, many nations in 2021 agreed to target methane for quick emission cuts as low hanging fruit in the global efforts to limit future warming to 1.5 or 2 degrees Celsius (2.7 or 3.6 degrees Fahrenheit) since pre-industrial times. The world has already warmed 1.1 to 1.2 degrees Celsius (about 2 to 2.2 degrees Fahrenheit). NOAA has been tracking methane levels in the air since 1983.

Methane makes up about a fifth of greenhouses gases. It is 23 times more powerful in terms of trapping heat in the atmosphere than carbon dioxide and lasts 12 years in the atmosphere before it oxidizes and converts to carbon dioxide and water. Levels of methane have increased over 150 percent since the pre-industrial age. Sources include flooded rice paddies, peat bogs, coal mining, rubbish heaps and melted permafrost. According to one estimate a third of the world’s methane may come from termite farts. Other animals also produce large amounts of methane (See Below).

Sources of Methane

Methane sources: agriculture (40 percent), fossil fuel (30 percent), water disposal (18 percent), land use and biomass burning (7 percent) and residential and commercial (5 percent). A recent study by German scientists a the Max Planck Institute in Heidelberg found 10 percent to 30 percent of new methane emissions come from plants. Concentrations of methane have tripled in the past 150 years.

About 14 percent of the global methane emissions come from farm animal flatulence and belches, mostly from cattle, dairy cows and sheep. Scientists at the Rowett Research Institure in Aberdeen, Scotland have come up with sweet-smelling food additives made with fumaric acids that reduce methane emissions by 70 percent. Japanese scientists at Obihiro University have made similar progress against belches using cysteine (a type of amino acid) and nitrates in cattle feed to suppress methane production during digestion so that the belches contain no methane.

Much of the methane produced by agriculture comes from paddy fields, so much so that rice emits more greenhouse gases than other crop. The source of the methane is bacteria that thrives in flooded paddies.

A 2021 United Nations report said that efforts to reduce methane emissions should be focused on reducing emissions from landfill sites and gas wells, cutting down food waste and loss, improving livestock management, and encouraging consumers to adopt diets with a lower meat and dairy content.

Methane Increased at Record Levels in 2021

According to the World Meteorological Organisation, methane levels in the atmosphere reached 1,889 parts per billion in 2021. Concentrations of CO 2 are roughly 200 times higher, but methane is calculated to be more than 80 times more potent at warming over a 20-year period.

NOAA estimated that levels of methane rose at a record pace in 2021. Associated Press reported: The preliminary airborne level of methane jumped 17 parts per billion, hitting 1895.7 parts per billion in 2021. It’s the second year in a row that methane rose at a record rate with 2020 going up 15.3 ppb over 2019. Methane levels are now way more than double pre-industrial levels of 720 parts per billion, said Lindsay Lan, an atmospheric scientist at NOAA and the University of Colorado. “This trend of accelerating increase in methane is extremely disturbing,” said Cornell University methane researcher Robert Howarth. [Source: Seth Borenstein, Associated Press, April 8, 2022]

“To limit warming to well-below 2C this century, we need to cut our methane emissions dramatically, and today we are clearly moving in the wrong direction,” climate scientist Zeke Hausfather of Stripe and Berkeley Earth said. “Cutting methane has strong immediate climate benefits, as it is the only greenhouse gas for which emission reductions can quickly cool the climate (versus slowing or stopping the rate of warming).”

Lan said early signs point more to natural causes for the methane jump, because of La Nina, the natural and temporary cooling of parts of the Pacific that change weather worldwide, but it’s still early. La Nina tends to make it rain more in some tropical regions and the two years in a row of record increases during La Nina points to methane escaping from wetlands, she said.

The key question is whether this increasing trend could add to climate change problems or is a pandemic-related blip due to the decrease in methane-destroying nitrous oxides from less car and industrial pollution, said Stanford University climate scientist Rob Jackson, “It seems to be something else instead of COVID,” Lan said. She figures high levels in 2020 and then even higher levels in 2021, when lockdowns were eased, point away from a pandemic effect.

Both fossil fuels and agriculture are key in methane increases, Howarth said. But he said, “my research strongly points toward fossil fuels as being the largest cause of the increase since 2008, with increase emissions from shale gas production from fracking in the U.S. being a major part of that.”

In a study in 2021, Lan looked at the chemical isotopes to isolate where steady increases in methane emissions since 2006 may be coming from. The chemical signature pointed away from fossil fuels as the bigger guilty party and more toward either natural wetland emissions or agriculture, she said.

Methane measurements from the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua Satellite

Global Warming, Coal and Fossil Fuels

Coal is one of the largest sources of global-warming-producing, greenhouse gases. Coal produces more carbon dioxide per unit than any other fossil fuel. Carbon dioxide emitted per kilowatt hour: 1) coal, 2.1; 2) petroleum, 1.4; 3) natural gas, 0.8. About a quarter of the world’s carbon dioxide emissions come from coal-burning power plants. All the use of coal together account for about 40 percent of carbon dioxide emissions. If new power plants are built the situation will get worse.

The new modern plants also still release millions of tons of carbon dioxide, as much as 11 million tons a year, only slightly less than similar sized plant built 30 years ago. Almost all the carbon dioxide is released in the atmosphere. There is no easy method to capture carbon dioxide and dispose of it.

The World Bank has issued warning abut the consequences of global warming and said the world must wean itself off fossil fuel but at the same time is funding new coal-fired plans in the developing countries such as India, South Africa and Botswana. Marianne Fay, the bank’s chief economist told the Times of London, “There are a lot poor countries which have coal reserves, and for them it’s the only option. Our policy is to continue finding coal to the extent that there no alternative and to push for the most efficient coal plants possible Frankly, ut would be immoral at this stage to say, “We want to have clean hands, therefore we are not going to touch coal.”

Food Production Generates More than a Third of Manmade Greenhouse Gases

Xiaoming Xu and Atul Jain wrote in The Conversation: “Food production is a big contributor to climate change, generating about 35 percent of total global man-made greenhouse gas emissions. Breaking down this share, production of animal-based foods – meat, poultry and dairy products, including growing crops to feed livestock and pastures for grazing – contributes 57 percent of emissions linked to the food system. Raising plant-based foods for human consumption contributes 29 percent. The other 14 percent of agricultural emissions come from products not used as food or feed, such as cotton and rubber. Overall, we calculated that the food system produces emissions that are equivalent to approximately 17.3 billion metric tons (17.318 teragrams) of carbon dioxide yearly.[Source: Xiaoming Xu, Postdoctoral Research Associate in Atmospheric Sciences, University of Illinois at Urbana-Champaign and Atul Jain, Professor of Atmospheric Sciences, University of Illinois at Urbana-Champaign, The Conversation, September 14, 2021]

“Land use change – clearing forests for farms and ranches, which reduces carbon storage in trees and soils – accounts for 29 percent of total food production greenhouse gas emissions. Another 38 percent comes from farmland management activities, such as plowing fields, which reduces soil carbon storage, and treating crops with nitrogen fertilizer. Farmers also burn a lot of fossil fuel to run their tractors and harvesters.

“Raising livestock generates 21 percent of greenhouse gas emissions from food production. It includes methane belched by grazing animals, as well as methane and nitrous oxide released from livestock manure. The remaining 11 percent comes from activities that occur beyond farm gates, such as mining, manufacturing and transporting fertilizers and pesticides, as well as energy use in food processing.

“Which foods generate the most greenhouse gas emissions? Among animal-based foods, beef is the largest contributor to climate change. It generates 25 percent of total food emissions, followed by cow milk (8 percent) and pork (7 percent). Rice is the largest contributor among plant-based foods, producing 12 percent of the total greenhouse gas emissions from the food sector, followed by wheat (5 percent) and sugarcane (2 percent). Rice stands out because it can grow in water, so many farmers flood their fields to kill weeds, creating ideal conditions for certain bacteria that emit methane.

“This helps to explain why South and Southeast Asia have the greatest food-production-related emissions by region, producing 23 percent of the global total. This region is the only place where plant-based emissions are larger than animal-based emissions. South America is the second-largest emitter at 20 percent, and has the largest emissions from animal-based food, reflecting the dominance of ranching there. Among individual countries, China, India and Indonesia have the highest emissions from plant-based food production, contributing 7 percent, 4 percent, and 2 percent respectively of global food-related greenhouse gas emissions. The countries with leading emissions from the production of animal-based foods are China (8 percent), Brazil (6 percent), the U.S. (5 percent) and India (4 percent).

“Worldwide, we estimate that humans are using 18 million square miles (4.6 billion hectares) of land to produce food – about 31 percent of Earth’s total land area, excluding areas covered by snow and ice. Of this, 30 percent is cropland and 70 percent is various types of grazing land. Looking at how these areas are managed, we estimate that 13 percent of total agricultural land is being used to produce plant-based foods. The other 77 percent is being used to produce animal-based foods, including croplands that are growing animal feed and grazing lands. The remaining 10 percent is being used to raise other products, such as cotton, rubber and tobacco.

Impact of Livestock and Cow Burps on Climate Change

Bovine emissions — cow belches, which emit methane — are a significant source of greenhouse The Humane Society International says the industry is responsible for 18 percent of greenhouse gas emissions, while a study published by the Journal of Ecological Society puts that figure at 87 percent. On top of the animals themselves, animal husbandry and livestock raising are leading forces behind deforestation. By one estimate 80 percent of the Amazon's deforestation takes place to provide land for cattle farming. In the United States, 41 percent of land is used for livestock pastures and feed crops. [Source: Kaitlin Reilly, Yahoo News, January 28, 2022]

"Without a doubt, humanity cannot survive on Earth without a massive reduction in animal product consumption," Greg Schwartz, a Laney College professor of environmental geography and advocate of a meat- and dairy-free lifestyle, known as Veganuary, told Yahoo Life. "Given the sobering statistics about animal agriculture’s devastating impact on the planet, going plant-based, especially as a denizen of Western countries with very high animal product consumption rates, has the most significant pro-planet effects of any lifestyle modification.

Schwartz estimates that the animal agriculture industry accounts for 40 percent of climate change. "Being a vegan who drives an SUV is more environmentally-friendly than being an omnivore who drives an electric car," he said. “The best way to be ecologically friendly and to lower your ecological footprint in general is to eat less meat and less animal products,” Schwartz says. “That’s at the top of the pyramid, because eating [animal products] is so harmful.”

““Of the meats, beef is clearly the worst in terms of consumption, in terms of wasting of calories, wasting of water. Cows are inefficient: They only produce about 6 percent of edible flesh from all of the calories they eat. They naturally take up a lot of land space, which is why you get a lot of that deforestation and altered land use.” According to Switch4Good, an organization seeking to eliminate dairy consumption, if everyone in the United States ate no meat or cheese for just one day per week, it would have the environmental benefit of not driving 91 billion miles or taking 7.6 million cars off the road.

Image Sources: World Meteorological Organization; National Oceanic and Atmospheric Administration (NOAA), Wikimedia Commons

World Meteorological Organization; National Oceanic and Atmospheric Administration (NOAA), Text Sources: New York Times, Washington Post, Los Angeles Times, Times of London, Yomiuri Shimbun, The Guardian, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated April 2022

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