Greenhouse gas emissions
Greenhouse gas 'emissions' from human activities intensify the greenhouse effect. This contributes to climate change. Carbon dioxide, from burning fossil fuels such as coal, oil, and natural gas, is the main cause of climate change. The largest annual emissions are from China followed by the United States. The United States has higher emissions per capita. The main producers fueling the emissions globally are large oil and gas companies. Emissions from human activities have increased atmospheric carbon dioxide by about 50% over pre-industrial levels. The growing levels of emissions have varied, but have been consistent among all greenhouse gases. Emissions in the 2010s averaged 56 billion tons a year, higher than any decade before. Total cumulative emissions from 1870 to 2022 were 703 , of which 484±20 from fossil fuels and industry, and 219±60 from land use change. Land-use change, such as deforestation, caused about 31% of cumulative emissions over 1870–2022, coal 32%, oil 24%, and gas 10%.
Carbon dioxide is the main greenhouse gas resulting from human activities. It accounts for more than half of warming. Methane emissions have almost the same short-term impact. Nitrous oxide and fluorinated gases play a lesser role in comparison. Emissions of carbon dioxide, methane and nitrous oxide in 2023 were all higher than ever before.
Electricity generation, heat and transport are major emitters; overall energy is responsible for around 73% of emissions. A growing concern for electricity usage is the expansion of artificial intelligence, which is projected to significantly increase global energy demand. Deforestation and other changes in land use also emit carbon dioxide and methane. The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Agricultural soils emit nitrous oxide partly due to fertilizers. Similarly, fluorinated gases from refrigerants play an outsized role in total human emissions.
The current -equivalent emission rates averaging 6.6 tonnes per person per year, are well over twice the estimated rate 2.3 tons required to stay within the 2030 Paris Agreement increase of 1.5 °C over pre-industrial levels. Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries.
The carbon footprint serves as an indicator to compare the amount of greenhouse gases emitted over the entire life cycle from the production of a good or service along the supply chain to its final consumption. Carbon accounting is a framework of methods to measure and track how much greenhouse gas an organization emits. This accounting is used to help understand the various effects of emissions on positive and negative impacts they have on the climate including on human mortality.
Relevance for greenhouse effect and global warming
Overview of main sources
Relevant greenhouse gases
The major anthropogenic sources of greenhouse gases are carbon dioxide, nitrous oxide, methane and three groups of fluorinated gases, hydrofluorocarbons and perfluorocarbons, and nitrogen trifluoride ). Though the greenhouse effect is heavily driven by water vapor, human emissions of water vapor are not a significant contributor to warming.Although CFCs are greenhouse gases, they are regulated by the Montreal Protocol which was motivated by CFCs' contribution to ozone depletion rather than by their contribution to global warming. Ozone depletion has only a minor role in greenhouse warming, though the two processes are sometimes confused in the media. In 2016, negotiators from over 170 nations meeting at the summit of the United Nations Environment Programme reached a legally binding accord to phase out hydrofluorocarbons in the Kigali Amendment to the Montreal Protocol. The use of CFC-12 has been phased out due to its ozone depleting properties. The phasing-out of less active HCFC-compounds will be completed in 2030.
Human activities
Starting about 1750, industrial activity powered by fossil fuels began to significantly increase the concentration of carbon dioxide and other greenhouse gases. Emissions have grown rapidly since about 1950 with ongoing expansions in global population and economic activity following World War II. As of 2021, measured atmospheric concentrations of carbon dioxide were almost 50% higher than pre-industrial levels.The main sources of greenhouse gases due to human activity are:
- Burning fossil fuels: Burning oil, coal and gas is estimated to have emitted 37.4 billion tonnes of -eq in 2023. The largest single source is coal-fired power stations, with 20% of greenhouse gases as of 2021.
- Land use change accounts for about a quarter of total anthropogenic GHG emissions.
- Livestock enteric fermentation and manure management, paddy rice farming, land use and wetland changes, human-made lakes, pipeline losses, and covered vented landfill emissions leading to higher methane atmospheric concentrations. Many of the newer style fully vented septic systems that enhance and target the fermentation process also are sources of atmospheric methane.
- Use of chlorofluorocarbons in refrigeration systems, and use of CFCs and halons in fire suppression systems and manufacturing processes.
- Agricultural soils emit nitrous oxide partly due to application of fertilizers.
- The largest source of anthropogenic methane emissions is agriculture, closely followed by gas venting and fugitive emissions from the fossil-fuel industry. The largest agricultural methane source is livestock. Cattle are the animal species responsible for the most emissions, representing about 65% of the livestock sector's emissions.
Global estimates
The current -equivalent emission rates averaging 6.6 tonnes per person per year, are well over twice the estimated rate 2.3 tons required to stay within the 2030 Paris Agreement increase of 1.5 °C over pre-industrial levels.
While cities are sometimes considered to be disproportionate contributors to emissions, per-capita emissions tend to be lower for cities than the averages in their countries.
A 2017 survey of corporations responsible for global emissions found that 100 companies were responsible for 71% of global direct and indirect emissions, and that state-owned companies were responsible for 59% of their emissions.
China is, by a significant margin, Asia's and the world's largest emitter; it emits nearly 10 billion tonnes each year, more than one-quarter of global emissions. Other countries with fast growing emissions are South Korea, Iran, and Australia. On the other hand, annual per capita emissions of the EU-15 and the US are gradually decreasing over time. Emissions in Russia and Ukraine have decreased fastest since 1990 due to economic restructuring in these countries.
2015 was the first year to see both total global economic growth and a reduction of carbon emissions.
High income countries compared to low income countries
Annual per capita emissions in the industrialized countries are typically as much as ten times the average in developing countries. Due to China's fast economic development, its annual per capita emissions are quickly approaching the levels of those in the Annex I group of the Kyoto Protocol.Africa and South America are both fairly small emitters, accounting for 3-4% of global emissions each. Both have emissions almost equal to international aviation and shipping.
Calculations and reporting
Variables
There are several ways of measuring greenhouse gas emissions. Some variables that have been reported include:- Definition of measurement boundaries: Emissions can be attributed geographically, to the area where they were emitted or by the activity principle to the territory that produced the emissions. These two principles result in different totals when measuring, for example, electricity importation from one country to another, or emissions at an international airport.
- Time horizon of different gases: The contribution of given greenhouse gas is reported as a equivalent. The calculation to determine this takes into account how long that gas remains in the atmosphere. This is not always known accurately and calculations must be regularly updated to reflect new information.
- The measurement protocol itself: This may be via direct measurement or estimation. The four main methods are the emission factor-based method, mass balance method, predictive emissions monitoring systems, and continuous emissions monitoring systems. These methods differ in accuracy, cost, and usability. Public information from space-based measurements of carbon dioxide by Climate Trace is expected to reveal individual large plants before the 2021 United Nations Climate Change Conference.
Reporting
Emissions may be tracked over long time periods, known as historical or cumulative emissions measurements. Cumulative emissions provide some indicators of what is responsible for greenhouse gas atmospheric concentration build-up.National accounts balance
The national accounts balance tracks emissions based on the difference between a country's exports and imports. For many richer nations, the balance is negative because more goods are imported than they are exported. This result is mostly due to the fact that it is cheaper to produce goods outside of developed countries, leading developed countries to become increasingly dependent on services and not goods. A positive account balance would mean that more production was occurring within a country, so more operational factories would increase carbon emission levels.Emissions may also be measured across shorter time periods. Emissions changes may, for example, be measured against the base year of 1990. 1990 was used in the United Nations Framework Convention on Climate Change as the base year for emissions, and is also used in the Kyoto Protocol. A country's emissions may also be reported as a proportion of global emissions for a particular year.
Another measurement is of per capita emissions. This divides a country's total annual emissions by its mid-year population. Per capita emissions may be based on historical or annual emissions.