Climate Matters•October 30, 2024
Heat-Trapping Pollution
KEY CONCEPTS
Greenhouse gases warm the Earth by trapping heat near the surface.
Heat-trapping greenhouse gases emitted by humans, mainly from burning fossil fuels, have led to rapid warming. Carbon dioxide and methane have contributed the most.
Global emissions and concentrations of greenhouse gases are higher than any point in the previous 800,000 years — and they continue to rise.
Most U.S. greenhouse gas emissions come from transportation, energy generation, and industry.
Greenhouse gases cause dangerous warming, but there are many options to rapidly cut emissions and choose a safer future.
Five things to know about greenhouse gases
1. Greenhouse gases warm the Earth by trapping heat near the surface.
Earth’s atmosphere contains a mix of gases that sustain life by absorbing some solar radiation, allowing living organisms to breathe, and transporting water.
One class of gases, known as greenhouse gases, traps heat near Earth’s surface. These heat-trapping greenhouse gases include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapor.
Each greenhouse gas differs in heat-trapping potential and the length of time that it remains in the atmosphere.
Greenhouse gases play a key role in regulating life-sustaining temperatures on Earth. Without any greenhouse gases, the energy that the Earth receives from the sun would radiate back into space, making our planet far too cold to support life. Too high a concentration, however, can trap a dangerous amount of heat.
Human activities since the Industrial Revolution — mainly the burning of fossil fuels such as coal, oil, and natural gas (mainly composed of methane gas) — have caused a sharp rise in atmospheric greenhouse gas concentrations and rapid warming.
Present-day concentrations of CO2, methane, and nitrous oxide are far higher than at any point during at least the last 800,000 years.
The excess heat that these greenhouse gases trap has led to rapid warming at rates not seen in at least the last 2,000 years — leading to many disruptive changes in our climate system, including more frequent and intense weather and climate extremes across the U.S. and around the world.
2. Greenhouse gases emitted by humans have already raised global temperatures. Carbon dioxide and methane have contributed the most.
Although a natural greenhouse effect has affected temperatures on Earth for millions of years, there is scientific consensus that human activities, particularly burning fossil fuels, is amplifying the natural greenhouse effect and causing rapid warming that goes far beyond natural variability.
Carbon dioxide, methane, and nitrous oxide are the three human-driven greenhouse gases that have contributed the most to global warming. The atmospheric concentration of each gas has increased more than 47%, 156%, and 23%, respectively, since 1850. Water vapor is the most abundant greenhouse gas in the atmosphere, but since human activity only has a small direct impact on its levels, it is not included in indicators of human-caused warming.
These three gases have caused a combined 1.6°C (2.9°F) of global warming since 1850.
The vast majority (95%) of this warming is due to CO2 and methane.
A small fraction of warming is masked by the cooling effects of aerosols, but as air quality standards improve, this contrasting impact is likely to decrease
Beyond emissions of these three important greenhouse gases, the net effect of all human activities (including land-use change and the cooling effect of aerosols and sulfur dioxide emissions) has warmed the planet by about 1.2°C (2.1°F) above pre-industrial levels.
This rapid warming is causing dangerous disruptions such as extreme heat, droughts, wildfires, more intense storms, and rising sea levels, which are projected to intensify if human-driven warming continues.
Carbon dioxide accounts for about 75% of global human-caused greenhouse gas emissions and has contributed the most to cumulative warming.
Methane and nitrous oxide constitute a much smaller portion of emissions, but they still have a considerable warming impact. Over a 20-year period, one metric ton of methane or nitrous oxide can trap about 80 times or 270 times the heat of one metric ton of CO2, respectively.
Because CO2 and methane are responsible for the majority of warming, reducing emissions of both is the best way to keep dangerous warming in check. Due to their dangerous effects on global climate, these greenhouse gases are widely regulated by the United Nations, with nearly 200 countries setting targets to reduce emissions of each.
Learn more: Solutions Series: Cutting Methane Emissions
3. Global emissions and concentrations of greenhouse gases are higher than ever before and continue to rise.
Atmospheric concentrations of CO2, methane, and nitrous oxide are far higher now than at any point over the last 2,000 years — and they have continued to rise, reaching new record highs.
The surge in greenhouse gas emissions has warmed the planet faster during the last 50 years than at any time in at least the past 2,000 years.
Such rapid changes in the climate pose significant hazards to human health, ecosystems, agriculture and food supplies, the economy, and more.
4. Most U.S. greenhouse gas emissions come from transportation, electric power, and industry.
The U.S. contributes significantly to global CO2 emissions, with both the highest cumulative emissions and the highest per-person emissions of any country.
The majority (76%) U.S. greenhouse gas emissions come from three sectors:
Transportation accounts for 28% of U.S. greenhouse gas emissions. About 97% of U.S. transportation emissions come from CO2 produced during the combustion of fossil fuels such as gasoline and diesel in internal combustion engines — mostly in cars and trucks.
Electric power produces one-quarter of U.S. greenhouse gas emissions. The electric power sector generates and distributes electricity to homes, businesses, factories, electric vehicles, and farming operations. About 97% of U.S. emissions from this sector are made up of CO2 from burning fossil fuels such as coal, oil, and natural gas to produce electricity.
Industry accounts for 23% of total U.S. emissions. The industrial sector produces goods and raw materials such as steel, cement, concrete, feedstock chemicals, minerals, and paper. Industrial emissions primarily come from CO2 produced during combustion of fossil fuels used to power factories and machinery. Other emissions leak from gas and oil systems or are generated during the production of chemicals, metals, and cement.
5. Greenhouse gases cause dangerous warming, but we have options to rapidly cut emissions and choose a safer future.
The actions that governments, industries, and individuals take now will significantly influence the future climate and impacts of dangerous warming. Continued emissions that drive the climate past 1.5°C (2.7°F) of global warming are predicted to cause unavoidable increases in climate hazards and related risks to natural ecosystems, human health, and livelihoods.
The impacts of a changing climate worsen with every bit of additional heat-trapping carbon pollution — which is why nearly 200 countries have agreed to keep global warming well below 2°C (3.6°F) with an aspirational limit of 1.5°C (2.7°F).
Although the U.S. has reduced emissions to roughly 17% below 2005 levels, this pace must more than triple for the remainder of this decade to meet national targets by 2030. Reaching these national targets requires action at the state and local levels.
There are many ways that we already know to reduce greenhouse gas emissions, especially across the sectors that account for most of current emissions. The solutions needed to accelerate the cutting of carbon from transportation, electricity, agriculture, and industry already exist — and are expanding across the country.
In much of the world, low-carbon renewable power sources are now cheaper than power from fossil fuels, providing even more reason to move away from fossil fuels.
If we commit to rapid and sustained cuts in carbon pollution now, it could set younger generations on a radically different path — toward a far safer future with less warming and fewer risky extreme weather events.
LOCAL STORY ANGLES
What is your city or state doing to reduce greenhouse gas emissions?
Is yours among the 22 states with official clean energy goals, the 24 states in the U.S. Climate Alliance, or the 33 states with Climate Action Plans? Search State Climate Policy Maps or the Database of State Incentives for Renewables & Efficiency for the status of climate action in all 50 states. State Climate Scorecards track each state’s progress toward official climate goals, broken out by sector.
See if your city has joined Cities Race to Zero, a UN-affiliated network of over one thousand cities around the world that have pledged to take significant action to reduce their greenhouse gas emissions. Organizing at the local and state levels can play a significant role in directly reducing emissions, increasing local support for larger policies, and serving as a model for other cities.
Explore major emitters of greenhouse gases
Explore greenhouse gas emissions from large facilities using this EPA resource to identify facilities in your region that may contribute significantly to greenhouse gas emissions.
CONTACT EXPERTS
Abhishek Chatterjee, PhD
Project Scientist
NASA Jet Propulsion Laboratory
Relevant expertise: global and regional greenhouse gas sources and sinks, urban greenhouse gas emissions
Contact: abhishek.chatterjee@jpl.nasa.gov
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
CO2 data is reported by NOAA’s Earth System Research Laboratory Global Monitoring Division. Calculations of average annual global temperature are performed independently at NASA and NOAA (among other groups). Climate Central combines these and compares temperatures to an earlier 1881-1910 baseline to assess warming closer to the preindustrial era.