Greenhouse gas emissions by the United States/ja

この記事は、 気候変動に寄与する米国からの温室効果ガスとその緩和策についてについての説明である。米国の気候変動全般については、 Climate change in the United States/jaを参照してください。

交通は米国の温室効果ガス排出源で最大である

米国の一人当たりおよびGDPあたりの排出量は大幅に減少しているが、排出量の純減はそれほど大きくない。

米国は、温室効果ガス排出量の多い国の中で、一人当たりの排出量が最も多い国の一つである。

米国は温室効果ガスであるメタンを含む天然ガスの主要生産国である。

米国の温室効果ガス排出量（経済部門別）

米国の年間CO2排出量は、人口が約4倍の中国の約3分の1である。

アメリカ合衆国は、2020年に52億メトリックトンの二酸化炭素換算温室効果ガス（GHG）排出量を排出し、世界第2位の排出国であり、中国の温室効果ガス排出量に次ぐ排出量であるとともに、一人当たりの温室効果ガス排出量が最も多い国の一つである。2019年には、中国が世界のGHGの27%を排出したと推定され、次いでアメリカ合衆国が11%、インドが6.6%であった。アメリカ合衆国は、これまで世界のGHGの4分の1を排出し、これは他のどの国よりも多い。年間排出量は一人当たり15トンを超え、上位8カ国の中で一人当たりの温室効果ガス排出量が最も多い国である。

IEAは、米国の最も裕福な10%の人々が、毎年一人当たり55トン以上のCO2を排出していると推定している。石炭火力発電所が徐々に閉鎖されているため、2010年代には発電からの排出量が、現在最大の排出源である交通機関に次ぐ2位に減少した。2020年には、アメリカ合衆国のGHG排出量の27%が交通機関から、25%が電力から、24%が産業から、13%が商業および住宅建築物から、11%が農業からであった。

米国のエネルギー関連CO2排出量は2023年に3%減少し、約1億3400万トン（MMmt）の削減となった。この削減は主に電力部門で発生し、石炭火力発電から太陽光や天然ガスなどのより持続可能なエネルギー源への大幅な転換が見られた。

2021年には、電力部門が米国の温室効果ガス排出源で2番目に大きく、米国の総排出量の25%を占めた。これらの温室効果ガス排出は、アメリカ合衆国における気候変動、および世界中の気候変動に寄与している。

Background

In context of climate change

US emissions of CO
2 and methane, 2018

Since 1850, the United States has cumulatively contributed the greatest amount of greenhouse gases of any nation or region.

Since 1850, the United States has cumulatively contributed the greatest amount of CO
2 of any nation.

Greenhouse gases absorb radiant energy from the Earth after the surface is warmed by sunlight. US emissions in 2022 involved carbon dioxide (CO
2, 79.7%), methane (CH
4, 11.1%), nitrous oxide (N
2O, 6.1%) and other gases (e.g., fluorinated gases, 3.1%).

Greenhouse gases vary in how long they remain in the atmosphere. Though methane and nitrous oxide are more potent greenhouse gasses than CO
2, CO
2 is longer-lived, remaining in the atmosphere for centuries. The average CO
2 concentration in 2024 was over 424 parts per million (ppm), and exceeded 427 ppm in February 2025—each more than 50% higher than its pre-industrial level. Annual US national CO
2 emissions were exceeded only by those of China, which has four times the US population. Regardless of where emissions occur, the emitted gases spread around the world. This anthropogenic (human-caused) increase in greenhouses gases has impacts on weather patterns, droughts, heat waves, wildfires, ocean acidification, sea level rise, glacial melting, average global temperatures, extinction of species, and so forth.

Sources of greenhouse gases

Carbon dioxide enters the atmosphere through the mass burning of fossil fuels such as coal, natural gas, and oil along with trees, solid waste, and biological materials. In 2018, carbon dioxide was estimated to approximately be 81% of all USA greenhouse gases emitted in 2018. Natural sinks and reservoirs absorb carbon dioxide emissions through a process called the carbon cycle. Sinks and reservoirs can include the ocean, forests and vegetation, and the ground.

Methane is mainly produced by livestock and agricultural practices. Methane was estimated to make up 10% of emitted greenhouse gases. From the decrease in non-agricultural GHG emissions during COVID-19, the percent of the USA's GHG emissions from livestock increased from 2.6% to about 5%, which is a smaller percentage than many other countries likely because the USA has more greenhouse gas emissions from vehicles, machines, and factories. Nitrous oxide is a greenhouse gas produced mainly by agriculture. Fluorinated gases are synthetically produced and used as substitutes for stratospheric ozone-depleting substances.

Greenhouse gases are produced from a wide variety of human activities, though some of the greatest impacts come from burning fossil fuels, deforestation, agriculture and industrial manufacturing. In the United States, power generation was the largest source of emissions for many years, but in 2017, the transportation sector overtook it as the leading emissions source. As of that year, the breakdown was transportation at 29%, followed by electricity generation at 28% and industry at 22%.

After carbon dioxide, the next most abundant compound is methane, though there have been methodological differences in how to measure its effects. According to a 2016 study, US methane emissions were underestimated by the EPA for at least a decade, by some 30 to 50 percent. Currently, the US government is working to reduce methane emissions in the agriculture, mining, landfill, and petroleum industries.

Another area of concern is that of ozone-depleting substances such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), which are often potent greenhouse gases with serious global warming potential (GWP). However, significant progress has been made in reducing the usage of these gases as a result of the Montreal Protocol, the international treaty that took effect in 1989.

Major emissions-creating events

In February 2018, an explosion and blowout in a natural gas well in Belmont County, Ohio was detected by the Copernicus Sentinel-5P satellite's Tropospheric Monitoring Instrument. The well was owned by XTO Energy. About 30 homes were evacuated, and brine and produced water were discharged into streams flowing into the Ohio River. The blowout lasted 20 days, releasing more than 50,000 tons of methane into the atmosphere. The blowout leaked more methane than is discharged by most European nations in a year from their oil and gas industries.

Per person, the United States generates carbon dioxide at a far faster rate than other primary regions.

Since 2000, rising CO
2 emissions in China and the rest of world have eclipsed the output of the United States and Europe.

Reporting requirement

Reporting of greenhouse gases was first implemented on a voluntary basis with the creation of a federal register of greenhouse gas emissions authorized under Section 1605(b) of the Energy Policy Act of 1992. This program provides a means for utilities, industries, and other entities to establish a public record of their emissions and the results of voluntary measures to reduce, avoid, or sequester GHG emission

In 2009, the United States Environmental Protection Agency established a similar program mandating reporting for facilities that produce 25,000 or more metric tons of carbon dioxide per year. This has resulted in thousands of US companies monitoring and reporting their greenhouse gas emissions, covering about half of all GHG emissions in the United States.

A separate inventory of fossil fuel CO
2 emissions is provided by Project Vulcan, a NASA/DOE funded effort to quantify North American fossil fuel emissions over time.

Mitigation

See also: Energy conservation in the United States and Climate change policy of the United States

Federal Policies

The United States government has held shifting attitudes toward addressing greenhouse gas emissions. The George W. Bush administration opted not to sign the Kyoto Protocol, but the Obama administration entered the Paris Agreement. The Trump administration withdrew from the Paris Agreement while increasing the export of crude oil and gas, making the United States the largest producer.

In 2021, the Biden administration committed to reducing emissions to half of 2005 levels by 2030. In 2022, President Biden signed the Inflation Reduction Act into law, which is estimated to provide around $375 billion over 10 years to fight climate change. 2022年現在 the social cost of carbon is 51 dollars a tonne whereas academics say it should be more than three times higher.

Cross-sectoral

• State and Local Climate and Energy Program
• Federal Energy Management Program

Transportation

The transportation sector accounted for nearly 29% of GHG emissions in the United States in 2019, with 58% of emissions coming from light-duty vehicles. 2021年現在, states lack legislation for low emission zones. Programs to reduce greenhouse gas emissions from the transportation sector include:

• The Corporate Average Fuel Economy (CAFE) Program: Requires automobile manufacturers to meet average fuel economy standards for the light-duty vehicles, large passenger vans and SUVs sold in the United States. Fuel economy standards vary according to the size of the vehicle.
• SmartWay: Helps improve environmental outcomes for companies in the freight industry.
• Renewable Fuel Standard: Under the Energy Policy Act of 2005, United States Environmental Protection Agency is responsible for promulgating regulations to ensure that gasoline sold in the United States contains a specific volume of renewable fuel.
• FreedomCAR and Fuel Partnership and Vehicle Technologies Program: The program works jointly with DOE's hydrogen, fuel cell, and infrastructure R&D efforts and the efforts to develop improved technology for hybrid electric vehicles, which include components (such as batteries and electric motors). The U.S. government uses six "criteria pollutants" as indicators of air quality: ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, particulate matter, and lead and does not include carbon dioxide and other greenhouse gases.
• Clean Cities: A network of local coalitions created by DOE in 1993 that works to support energy efficiency and clean fuel efforts in local transportation contexts.
• Congestion Mitigation and Air Quality Improvement (CMAQ) Program: Provides funds to states to improve air quality and congestion through the implementation of surface transportation projects (e.g., traffic flow and public transit improvements).
• Aviation industry regulation: Emissions from commercial and business jets make up 10% of U.S. transportation sector emissions and 3% of total national GHG emissions. In 2016, the EPA issued an "endangerment finding" that allowed the agency to regulate aircraft emissions, and the first proposed standards under that legal determination were issued in July 2020.
• Developing alternative energy sources: The Department of Energy's Bioenergy Technologies Office (BETO) supports research into biofuels as part of that agency's efforts to reduce transportation-related GHG emissions.
• Diesel Emissions Reduction Act (DERA) Program: Provides grants for diesel emissions reduction projects and technologies.

Energy consumption, residential and commercial

As of 2020, buildings in the United States consume roughly 40% of the country's total electricity and contribute a similar percentage of GHG emissions.

• EPA and DOE Clean Energy Programs – Energy Star
• Commercial Building Integration
• Residential Building Integration
• Weatherization Assistance Program
• State Energy Program

Energy consumption, industrial

• Energy Star for industry
• Industrial Technologies Program (ITP)

Energy supply

Total wind+solar electricity generation now exceeds coal-based energy in the U.S.

CO₂ emissions from the US electric power sector

• The Coalbed Methane Outreach Program (CMOP) works to reduce methane released into the atmosphere as a result of coal mining by supporting recovery of naturally occurring coal mine gases and encouraging the production of coalbed methane energy, among other uses.
• Natural Gas STAR Program
• The government also supports alternative energy sources that do not rely on fossil fuels, including wind power, solar power, geothermal power, and biofuel.
• These clean energy sources can often be integrated into the electric grid in what are known as distributed generation systems.
• EPA Clean Energy Programs - Green Power Partnership
• EPA Clean Energy Programs - Combined Heat and Power Partnership
• Carbon capture and storage Research Program
  • Advanced Energy Systems Program
  • CO₂ Capture
  • CO₂ Storage

Agriculture

• Environmental Quality Incentives Program
• Conservation Reserve Program
• Conservation Security Program
• AgSTAR Program

Forestry

• Healthy Forests Initiative
• Forest Land Enhancement Program

Waste management

• The Landfill Methane Outreach Program (LMOP) promotes the use of landfill gas, a naturally occurring byproduct of decaying landfill waste, as a sustainable energy source. Besides reducing emissions, landfill gas utilization has also been credited for reductions in air pollution, improvements to health and safety conditions, and economic benefits for local communities.
• In addition to reducing emissions from waste already in landfills, the EPA's WasteWise program works with businesses to encourage recycling and source reduction to keep waste out of landfills in the first place.

Regional initiatives

• Western Climate Initiative
• The Regional Greenhouse Gas Initiative (RGGI), founded in 2007, is a state-level emissions capping and trading program by nine northeastern U.S. states: Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New York, Rhode Island, Vermont, and Virginia. It is a cap and trade program in which states "sell nearly all emission allowances through auctions and invest proceeds in energy efficiency, renewable energy and other consumer benefit programs."
• Western Governors Association Clean and Diversified Energy Initiative
• Powering the Plains
• Carbon Sequestration Regional Partnerships
• U.S. Mayors Climate Protection Agreement
• National Governors Association's (NGA) Securing a Clean Energy Future.

State Policies

California

• Vehicle Air Pollution (Senate Resolution 27): States and implies that California does not have to adhere to cutbacks in federal emissions standards, thereby allowing stricter California emissions standards than the federal government. This Senate Resolution stems from the previous administration's efforts to reverse environmental policies, and in this case, vehicle emissions standards. California's authority to set its own emissions standards is allowed through California's Clean Air Act preemption waiver granted to the state by the EPA in 2009.  California's waiver applies to vehicles made in 2009 and later. The previous state standard included a goal for certain vehicles to reach an average 35 miles per gallon. California saw a large decline in vehicle emissions from 2007 to 2013 but a rise in emissions following 2013, which can be attributed to different circumstances, some of which include population and employment growth, and increases in overall state GDP indicating more economic activity in the state.
• Cap-and-Trade Program: Market-based carbon pricing program that sets a statewide cap on emissions. This cap declines annually and applies to large emitters that account for over 80 percent of California's GHG emissions. The California Air Resources Board (CARB) creates an allowance for each ton of carbon dioxide emissions. The number of allowances decreases over time and incentivizes a flexible approach to emissions reduction through trading.
• Advanced Clean Cars: Addresses GHG emissions and criteria air pollutants in California through the Low-Emission Vehicle (LEV) regulation and the Zero-Emission Vehicle (ZEV) regulation. The LEV regulation establishes increasing emissions standards for passenger vehicles through model year 2025. The ZEV regulation requires vehicle manufacturers to sell a certain percentage of ZEVs and plug-in hybrids annually through 2025. The next iteration of this program for future model years is under development. 15 states have adopted the regulations under this program.
• Advanced Clean Cars II: Mandates a ban on the sale of internal combustion engine passenger vehicles, trucks, and SUVs starting in 2035, and mandates annual increases in ZEV sales targets from model year 2026 to 2035. California has adopted the regulation and New York announced that it would follow.
• Advanced Clean Trucks: Requires manufacturers of medium-and heavy-duty trucks to sell an increasing percentage of zero-emission trucks each year starting with model year 2024. In addition to California, Oregon, Washington, New Jersey, New York, and Massachusetts have also adopted this regulation. 10 other states and the District of Columbia intend to adopt in the future.
• Low Carbon Fuel Standard (LCFS): Establishes annual targets through 2030 to ensure transportation-related fuels become cleaner and less carbon intensive. Oregon has a similar program entitled, Clean Fuels Program, which runs until 2025.
• In 2006, the state of California passed AB-32 (Global Warming Solutions Act of 2006), which requires California to reduce greenhouse gas emissions. To implement AB-32, the California Air Resources Board proposed a carbon tax but this was not enacted.
• In May 2008, the Bay Area Air Quality Management District, which covers nine counties in the San Francisco Bay Area, passed a carbon tax on businesses of 4.4 cents per ton of CO₂.

Colorado

In November 2006, voters in Boulder, Colorado, passed what is said to be the first municipal carbon tax. It covers electricity consumption with deductions for using electricity from renewable sources (primarily Xcel's WindSource program). The goal is to reduce their emissions by 7% below 1990 levels by 2012. Tax revenues are collected by Xcel Energy and are directed to the city's Office of Environmental Affairs to fund programs to reduce emissions.

Boulder's Climate Action Plan (CAP) tax was expected to raise $1.6 million in 2010. The tax was increased to a maximum allowable rate by voters in 2009 to meet CAP goals. As of 2017 the tax was set at $0.0049 /kWh for residential users (avg. $21 per year), $0.0009/kWh for commercial (avg. $94 per year), and $0.0003 /kWh for industrial (avg. $9,600 per year). Tax revenues were expected to decrease over time as conservation and renewable energy expand. The tax was renewed by voters on 6 November 2012.

As of 2015, the Boulder carbon tax was estimated to reduce carbon output by over 100,000 tons per year and provided $1.8 million in revenue. This revenue is invested in bike lanes, energy-efficient solutions, rebates, and community programs. The surcharge has been generally well received.

Maryland

In May 2010, Montgomery County, Maryland, passed the nation's first county-level carbon tax. The legislation required payments of $5 per ton of CO₂ emitted from any stationary source emitting more than a million tons of carbon dioxide per year. The only source of emissions fitting the criteria is an 850 megawatt coal-fired power plant then owned by Mirant Corporation. The tax was expected to raise between $10 million and $15 million for the county, which faced a nearly $1 billion budget gap.

The law directed half of tax revenues toward low interest loans for county residents to invest in residential energy efficiency. The county's energy supplier buys its energy at auction, requiring the plant owner to sell its energy at market value, preventing any increase in energy costs. In June 2010, Mirant sued the county to stop the tax. In June 2011 the Federal Court of Appeals ruled that the tax was a fee imposed "for regulatory or punitive purposes" rather than a tax, and therefore could be challenged in court. The County Council repealed the fee in July 2012.

GHG reduction targets

• States with statutory GHG reduction targets: California, Colorado, Connecticut, Hawaii, Maryland, Maine, Minnesota, Massachusetts, New Jersey, New York, Nevada, Oregon, Rhode Island, Vermont, Virginia, and Washington.
• States that don't have statutory targets, but have statutory GHG reporting requirements: Iowa and Pennsylvania.

Renewable portfolio standards

• 38 states have established renewable portfolio standards or voluntary targets, which increase the share of renewable electricity generation over time.

Lead by example programs

• New Hampshire's Better Buildings Neighborhood Program
• New Jersey's Clean Energy Program
• Atlanta's Virginia Highland - 1st Carbon Neutral Zone in the United States

Local programs

Municipal, county, and regional governments have substantial influence on greenhouse gas emissions, and many have reduction goals and programs. Local governments are often one of the largest employers in their jurisdictions, and can achieve substantial reductions in their own operations, such as by using zero-emissions vehicles, making government buildings energy-efficient, making or buying renewable energy, and providing incentives for employees to walk, bike, or take transit to work. Local governments have control over several policy areas which influence emissions for the population as a whole. These include land use regulations such as zoning; transportation infrastructure like public transit, parking, and bike lanes; and building codes and efficiency regulations. Some municipalities act as utility cooperatives and set a minimum standard for renewable generation. Although healthier air is the main benefit of clean air zones in cities they can have a side effect of reducing greenhouse gas emissions: however as of 2025 it is unclear whether cities in the US have the political power to make clean air zones.

Non-governmental responses

Individual action

See also: Individual action on climate change

Actions taken by individuals on climate change include diet, travel alternatives, household energy use, reduced consumption and family size. Individuals can also engage in local and political advocacy around issues of climate change. Individuals have a variety of carbon offsetting options available to mitigate their environmental impact through non-profit organizations.

Business community

See also: Business action on climate change

Numerous large businesses have started cutting emissions and committed to eliminate net emissions by various dates in the future, resulting in higher demand for renewable energy and lower demand for fossil fuel energy. Businesses may also go carbon neutral by enrolling in Carbonfree® Programs or certifying their products as Carbonfree®

Technologies in development

• Carbon Sequestration Regional Partnerships
• Nuclear:
  • Generation IV Nuclear Energy Systems Initiative
  • Nuclear Hydrogen Initiative{
  • Advanced Fuel Cycle Initiative
  • Global Nuclear Energy Partnership{
• Clean Automotive Technology
• Hydrogen Technology
• High-temperature superconductivity

See also

• Climate Registry
• Coal in the United States
• Energy conservation in the United States
• Greenhouse gas emissions in Kentucky
• List of U.S. states by carbon dioxide emissions
• Phase-out of fossil fuel vehicles
• Plug-in electric vehicles in the United States
• Politics of global warming
• Regulation of greenhouse gases under the Clean Air Act
• Select Committee on Energy Independence and Global Warming
• U.S. Climate Change Science Program
• List of coal-fired power stations in the United States
• List of natural gas-fired power stations in the United States

External links

• Inventory by Climate Trace
• Live carbon emissions from electricity generation
• Carbon dioxide emissions by fuel (Energy Information Administration).