Carbon monitoring refers to tracking how much carbon dioxide or methane is produced by particular activity at a particular point in time. For example, it may refer to tracking methane emissions from agriculture, or carbon dioxide emissions from land use changes, such as deforestation, or from burning fossil fuels, whether in a power plant, automobile, or other device. Because carbon dioxide is the greenhouse gas emitted in the largest quantities, and methane is an even more potent greenhouse gas, monitoring carbon emissions is widely seen as crucial to any effort to reduce emissions and thereby slow climate change. Monitoring carbon emissions is key to the cap-and-trade program currently being used in Europe, as well as the one in California, and will be necessary for any such program in the future, like the Paris Agreement. The lack of reliable sources of consistent data on carbon emissions is a significant barrier to efforts to reduce emissions.
Sources of such emissions data include:
Carbon Monitoring for Action (CARMA) – An online database provided by the Center for Global Development, that includes plant-level emissions for more than 50,000 power plants and 4,000 power companies around the world, as well as the total emissions from power generation of countries, provinces (or states), and localities. Carbon emissions from power generation account for about 25 percent of global CO2 emissions.
ETSWAP - An emissions monitoring and reporting system currently in use in the UK and Ireland, which enables relevant organizations to monitor, verify and report carbon emissions, as is required by the EU ETS (European Union Emissions Trading Scheme).
In the United States
Almost all climate change regulations in the US have stipulations to reduce carbon dioxide and methane emissions by economic sector, so being able to accurately monitor and assess these emissions is crucial to being able to assess compliance with these regulations. Emissions estimates at the national level have been shown to be fairly accurate, but at the state level there is still much uncertainty. As part of the Paris Agreement, the US pledged to "decrease its GHG emissions by 26–28 % relative to 2005 levels by 2025 as part of the Paris Agreement negotiated at COP21. To comply with these regulations, it is necessary to quantify emissions from specific source sectors. A source sector is a sector of the economy that emits a particular greenhouse gas, i.e. methane emissions from the oil and gas industry, which the US has pledged to decrease by 40–45 % relative to 2012 levels by 2025 as a more specific action towards achieving its Paris Agreement contribution.
Currently, most governments, including the US government, estimate carbon emissions with a "bottom-up" approach, using emission factors which give the rate of carbon emissions per unit of a certain activity, and data on how much of that activity has taken place. For example an emission factor can be determined for the amount of carbon dioxide emitted per gallon of gasoline burned, and this can be combined with data on gasoline sales to get an estimate of carbon emissions from light duty vehicles. Other examples include determining the number of cows in various locations, or the mass of coal burned at power plants, and combining these data with the appropriate emissions factors to estimate methane or carbon dioxide emissions. Sometimes "top-down" methods are used to monitor carbon emissions. These involve measuring the concentration of a greenhouse gas in the atmosphere and using these measurements to determine the distribution of emissions which caused the resulting concentrations.
Accounting by sector can be complicated when there is a chance of double counting. For example, when coal is gasified to produce synthetic natural gas, which is then mixed with natural gas and burned at a natural gas powered power plant, if accounted for as part of the natural gas sector, this activity must be subtracted from the coal sector and added to the natural gas sector in order to be properly accounted for.
In the European Union
As part of the European Union Emission Trading Scheme (EU-ETS), carbon monitoring is necessary in order to ensure compliance with the cap-and-trade program. This carbon monitoring program has three main components: atmospheric carbon dioxide measurements, bottom-up carbon dioxide emissions maps, and an operational data-assimilation system to synthesize the information from the first two components.
The top-down, atmospheric measurement approach involves satellite data and in-situ measurements of carbon dioxide concentrations, as well as atmospheric models that model atmospheric transport of carbon dioxide. These have limited ability to determine carbon dioxide emissions at highly resolved spatial scales and can typically not represent finer scales than a 1 km grid. The models also must resolve the fluxes of carbon dioxide from anthropogenic sources like fossil fuel burning, and from natural interactions like terrestrial ecosystems and the ocean. Due to the complexities and limitations of the top-down approach, the EU combines this method with a bottom-up approach.
The current bottom-up data are based on information that is self-reported by emitters in the trading scheme. However, the EU is trying to improve this information source and has proposed plans for improved bottom-up emissions maps, which will have greatly improved spatial resolution and near real-time updates.
An operational data system to combine the information gathered from the two aforementioned sources is also planned. The EU hopes that by the 2030s, this will be operational and enable a highly sophisticated carbon monitoring program across the European Union.
Satellites can be used to monitor carbon dioxide concentrations from outer space, and have been shown to be as accurate as Earth-based measurement systems. NASA currently operates a satellite named the Orbiting Carbon Observatory-2 (OCO-2), and Japan operates their own satellite, the Greenhouse Gases Observing Satellite (GOSAT). These satellites can provide valuable information to fill in data gaps from emission inventories. The OCO-2 measured a strong flux of carbon dioxide over the Middle East, which had not been represented in emissions inventories, indicating that important sources were being neglected in bottom-up estimates of emissions. These satellites currently both have an error of only 0.5% in the measurements, but the American and Japanese teams hope to bring that error down to 0.25%. China recently launched their own satellite to monitor greenhouse gas concentrations on Earth, the TanSat, in December 2016. It currently has a three-year mission planned and will take readings of carbon dioxide concentrations every 16 days.
- "Global Carbon Monitoring System Fact Sheet". climatechange.gov.au. Department of Climate Change and Energy Efficiency. Archived from the original on November 20, 2008.
- IPCC (2014). "Summary for Policy Makers" (PDF). Intergovernmental Panel on Climate Change.
- "Irish and British aviation emissions cutting work underway". Edie.net. Retrieved 2013-09-08.
-  Archived March 30, 2012, at the Wayback Machine.
- Miller, Scot M. (March 2017). "Constraining sector-specific CO2 and CH4 emissions in the US" (PDF). Atmospheric Chemistry and Physics. doi:10.5194/acp-17-3963-2017.
- "The Paris Agreement". United Nations Framework Convention on Climate Change.
- "EPA Releases First-Ever Standards to Cut Methane Emissions from the Oil and Gas Sector". US Environmental Protection Agency.
- "Greenhouse Gas Emissions from a Typical Passenger Vehicle" (PDF). US Environmental Protection Agency.
- "CO2 Report" (PDF). European Union.
- "Next generation of carbon-monitoring satellites faces daunting hurdles". Nature.
- "Earth Observatory". NASA.
- "China launches carbon dioxide monitoring satellite". Physics.com. Archived from the original on 2016-12-23.