Greenhouse gas emissions come from human activities like burning fossil fuels and can be measured in terms of carbon dioxide (CO2).
The Environmental Protection Agency has long monitored sources of greenhouse gases through their National Emissions and Sinks Inventory dating back to 1990. Visit their Greenhouse Gas Inventory Data Explorer to create personalized graphs and follow trends over time.
Carbon Dioxide
Carbon dioxide, commonly abbreviated CO2, is a colorless gas and one of the main constituents of Earth’s atmosphere. It is produced through combustion of carbon-containing fuels as well as plant respiration and fermentation processes, helping block radiant energy that would otherwise escape out into space by passing through our atmosphere unimpeded. As of March 2018, carbon dioxide concentration levels are at their all-time high levels.
Air bubbles trapped within mile-thick ice cores indicate that atmospheric carbon dioxide levels rarely exceeded 300 parts per million (ppm). Since the Industrial Revolution began, however, they have increased to 400 parts per million and this increased greenhouse effect is driving global temperatures upward.
One-fifth of manmade carbon dioxide emissions come from burning fossil fuels like coal, oil and natural gas; another quarter comes from land-use changes, including clearing forests to make way for agriculture and other uses; some carbon dioxide may even end up stored in dead and decaying plant matter as it decomposes, eaten by animals that then store or release their stores back into soils and oceans through volcanoes over thousands or millions of years.
Arrhenius proposed that the removal of some carbon dioxide from Earth’s atmosphere could help bring temperatures back down to levels that had produced ice age cycles in the past. His calculation involved a complex mathematical procedure using estimates for how carbon is recycled through Earth’s natural systems like volcanic eruptions and ocean uptake.
Today, approximately one third of carbon emissions come from human activities in North America and Europe, with the remaining third coming from rapidly emerging economies like China and India. If current emission trends continue at their current pace, carbon dioxide concentration in the atmosphere may peak by 2050 at approximately 750 parts per million and remain there or higher for many millennia after. This would cause irreversible climate change that will leave lasting legacies from our choices today.
Methane
Methane, second only to carbon dioxide as a greenhouse gas, is the second-most prominent global warming gas on Earth. Like CO2, methane is colorless and odorless gas produced both naturally (such as when plants decompose underwater in wetlands) and industrially (natural gas is mostly composed of methane). But over shorter timescales — approximately 10 years instead of centuries for CO2–methane can be 25 times more potent at warming the atmosphere than carbon dioxide.
Methane emissions worldwide are on an exponential increase. Between 2020 and 2021, global average atmospheric concentration of methane increased by 18-15 ppb respectively; one possible explanation could be climate feedback loops wherein as our planet becomes warmer, organic material decomposes faster leading to increased methane emission levels.
Human-caused methane emissions stem largely from rice farming, raising cattle, and energy production–especially by burning fossil fuels such as coal, oil and natural gas. Methane can also escape through leaks in natural gas pipelines or oil wells or through leaky natural gas pipelines or wells or through natural processes in termite colonies or the digestive processes of ruminant animals such as termites.
Scientists are modeling the long-term impacts of methane emissions and discovering that they may have greater warming impacts than initially assumed. Many countries have pledged to reduce methane emissions as part of the Paris Agreement and over 100 nations have signed the Global Methane Pledge as a result.
Methane emissions can be significantly reduced through shifting to plant-based agriculture and decreasing animal feed intake (e.g. by giving cows less grain and more grass), improving waste management at landfills, installing technologies to capture methane for use later, or installing technologies that capture and sell it back out for other uses – among many other measures. One promising tool is “methane fees,” often combined with existing business taxes in extractive industries like coal mining or oil drilling; our Staff Climate Note contains this chart showing their potential to reduce methane emissions dramatically!
Nitrous Oxide
Nitrous oxide, commonly referred to as laughing gas, is an extremely potent greenhouse gas capable of trapping 300 times more heat in the atmosphere than carbon dioxide and contributing to ground-level ozone formation. Although carbon dioxide and methane remain the predominant greenhouse gases associated with human activities, emissions of nitrous oxide are growing quickly due to synthetic fertilizer usage in agriculture and livestock ranching operations.
Nitrous oxide is produced naturally by soil microbes, but its release can be stimulated through synthetic nitrogen fertilizers or by denitrifying and nitrifying organic nitrogen (such as animal manure). Nitrous oxide may also be generated experimentally via zinc on dilute nitric acid or hydroxylamine hydrochloride on sodium nitrite.
Chemiluminescence is an easy and straightforward method for measuring nitrous oxide concentration levels in the atmosphere, and the intensity of its emitted light relates directly to oxygen content present. Simply injecting small amounts of nitric oxide into the air then monitoring their activated molecules emitting light signals can provide a rapid measurement.
Nitrous oxide serves numerous legitimate uses, from hospital anesthetics and motor racing engine performance enhancement, to fumigant usage in food industries and soil pest control. Nitrous oxide gas comes in cartridges or cylinders for these uses. Furthermore, its use as an anesthetic in hospitals as well as soil pesticide use makes this substance highly versatile.
California accounts for roughly 8% of total greenhouse gas emissions from agriculture, with most coming from animal and crop agriculture. Like carbon dioxide, nitrous oxide is also considered a greenhouse gas; therefore its atmospheric concentrations increase when other greenhouse gases decrease or as water vapor increases in the air.
To reduce nitrous oxide production, one of the key strategies is maintaining accurate nutrient management. Appropriate fertilization rates will help limit emissions without impacting crop yield or quality; this can be accomplished through monitoring and following recommended nitrate application guidelines for each crop in question.
Fluorinated Gases
Fluorinated greenhouse gases such as fluorinated hydrofluorocarbons are potent greenhouse gases that linger in the atmosphere for long periods. Their global warming potential is up to 25 times greater than carbon dioxide. F-gases, or human-made chemicals known collectively as F-gases, include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3) which are released into the environment through leaks as well as disposal of appliances that use them.
HFCs are widely used in refrigeration systems and the production of aerosol propellants, foam blowing agents and solvents; they’ve also become an alternative to chlorofluorocarbons and halons which have been phased out under an international agreement known as the Montreal Protocol. Their low ozone-depleting potential makes these chemicals ideal replacements. Furthermore, HFCs boast very high global warming potentials; small changes to atmospheric concentration can have substantial ramifications on global temperatures; furthermore they have long atmospheric lifetimes; lasting years on end.
HFC-134a is one of the most commonly used F-gases, accounting for half of emissions and 86% of consumption by Global Warming Potential (GWP). Major sources include air conditioning equipment in vehicles and buildings, fire extinguishers, and thermal insulation foams; though refrigerant gas emissions contribute only a fraction to their climate impact; most impact comes from indirect CO2 emissions arising from electricity usage when maintaining refrigeration systems.
Overall, F-gas emissions rose approximately 105% between 1990 and 2021. This growth was fueled by an unprecedented 349% rise in HFCs since they are widely used as replacements for ozone-depleting substances. PFC and SF6 emissions declined during this time due to reduction efforts made by aluminum production facilities as well as electrical transmission and distribution businesses; such efforts include using alternative refrigerants that reduce energy use as well as retrofitting equipment to lower its energy needs and recycling or disposing of end of life equipment.