August 13, 2021
Today, human sources are responsible for 60% of global methane emissions, mainly from fossil fuel burning, landfill decomposition and agriculture. Almost a quarter of methane emissions can be attributed to agriculture, much of which comes from livestock. Rice growing and food waste are also major sources of agricultural methane as nearly a third of all food produced for human consumption is lost or wasted.
At NASA, scientists are studying the global methane budget to better understand the main sources of methane emissions and their contribution to climate change. In addition to human sources, methane is also produced in natural environments. The largest natural source of methane is wetlands, which contribute 30% of global methane emissions. Other natural sources of methane emissions are the oceans, termites, permafrost, vegetation, and forest fires.
Atmospheric methane concentrations have more than doubled since the industrial revolution due to the intensive use of oil, gas and coal, the increasing demand for beef and dairy products, and the increased production of food and organic waste. Although the increase in atmospheric methane concentration towards the end of the 20th is warming.
ASA’s new three-dimensional portrait of methane shows the world’s second largest contribution to greenhouse warming as it travels through the atmosphere. By combining multiple datasets from emissions inventories and simulations of wetlands in a high-resolution computer model, researchers now have an additional tool to understand this complex gas and its role in the earth’s carbon cycle, atmospheric composition and climate system. The new data visualization creates a more complete picture of the variety of methane sources on the ground and how the gas behaves as it moves through the atmosphere. Credits: NASA / Scientific Visualization Studio This video can be downloaded from NASA’s Scientific Visualization Studio
The greenhouse effect and methane
Greenhouse gases, including methane, contribute to chemical reactions and climate feedback. The greenhouse gas molecules capture solar energy by acting like a thermal blanket. The sun’s energy is absorbed by the earth’s surface, although some of this energy is reflected back into the atmosphere. The absorbed energy is also re-emitted at infrared wavelengths. Some of the reflected and re-emitted energy is released back into space, but the rest is trapped in the atmosphere by greenhouse gases. Over time, the trapped heat warms our climate and increases global temperatures.
Greenhouse gases in our atmosphere act like a blanket that traps the warmth of the sun. This causes global temperatures to rise as the amount of greenhouse gases increases.Credits: NASA / Jesse Kirsch
The man-made rise in temperature can affect the methane released from natural sources. For example, permafrost can naturally thaw and emit methane into the atmosphere, but humans have increased the rate at which permafrost thaws due to man-made warming.
Methane is the world’s second largest cause of global warming after carbon dioxide. Although carbon dioxide is more abundant in the atmosphere than methane, a single methane molecule traps heat more effectively than a single carbon dioxide molecule.
However, the lifespan of a methane molecule is shorter than that of a carbon dioxide molecule because natural chemical processes remove methane from the atmosphere faster than carbon dioxide. This means that if methane emissions were reduced and methane was naturally chemically cleaned, atmospheric methane could drop dramatically in just ten years. Reducing the amount of methane released into the atmosphere could have a significant and almost immediate impact in reducing the short-term effects of climate change and help keep global temperature change below 2 degrees Celsius.
Why cows produce methane
Cattle such as dairy cows or beef cattle produce methane as a by-product of digestion. Cattle are ruminants, which means they have a special digestive system that allows them to process foods that humans and most other animals cannot digest, such as fresh grass and undercooked grains. When food gets into a cattle’s stomach, it goes through a process called enteric fermentation: microbes and bacteria partially break down the food particles, which then ferment in the part of the stomach called the rumen. When the food particles ferment, they produce methane. Every time cattle burp – and to a lesser extent puff – methane is emitted and released into the atmosphere, where it acts as a greenhouse gas.
Facts about methane: methane has been responsible for 20% of global warming since the industrial revolution; In 2018, the food system contributed 33% of all man-made greenhouse gas emissions; In 2015, livestock accounted for 10% of methane emissions in the US; Methane is about 30 times stronger than CO2 over a century; Europe and the Arctic are the only two regions whose methane emissions fell between 2000 and 2018; Atmospheric methane concentrations have more than doubled over the past 200 years. Credits: NASA / Jesse Kirsch
NASA’s eyes on methane
While methane concentrations are well monitored, emissions must be inferred from a variety of factors. NASA scientists use a variety of methods to track methane emissions. To get the most accurate estimates possible, they use emissions inventories from countries around the world, simulate methane emissions from wetlands, and combine them with ground, air and satellite data using atmospheric models.
In California (and some other regions) researchers fly aircraft equipped with NASA’s Airborne Visible Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) and collect highly calibrated data. This data is used in the California Methane Survey, a joint venture between NASA, the California Air Resources Board, and the California Energy Commission, to quickly identify and report methane leaks.
In Alaska and northwestern Canada, NASA researchers are using satellites, aircraft and field research to better understand methane emissions from thawing permafrost as part of the Arctic Boreal and Vulnerability Experiment (ABoVE). Researchers have found that the carbon-rich permafrost is thawing at an increasing rate, likely as a result of man-made climate change, making the Arctic a major potential source of methane emissions. According to scientific estimates, the soils of this region store five times more carbon than has been emitted by all human activities in the last 200 years.
NASA researchers combine data from missions like ABoVE and the California Methane Survey with their knowledge of methane behavior in the atmosphere to create methane computer models. These models can help scientists and policy makers understand past, current, and future atmospheric methane patterns.
Ways to reduce methane emissions
Researchers in a variety of fields have been looking for possible solutions to reduce global methane emissions. For example, biogas plants reduce methane emissions by converting waste from livestock, plants, water and food into energy. Biogas is produced through the same natural process that occurs in landfills to break down organic waste. However, biogas plants take advantage of the resulting gas and use it as a clean, renewable and reliable source of energy instead of releasing it into the atmosphere as a greenhouse gas.
A study led by Professor Ermias Kebreab of the University of California-Davis found that adding a few ounces of algae to beef cattle diets could reduce their methane emissions by over 82%.
These types of technological – and biological – innovations can provide decision makers, ranchers, and others with more options for managing our future methane.
Credits: NASA / Jesse Kirsch / courtesy of Tracy Schohr
by Emily Fischer
NASA’s Earth Science News Team