How are greenhouse gas emissions monitored?

In this week’s Climate Now debate, we heard how the process of monitoring greenhouse gas emissions is fundamental to pinpointing the world’s biggest emitters and spurring action to bring about reductions. You can watch the highlights of the live debate in the video at the top of this article.

Our panellists spoke about improved satellite technology with global coverage that can precisely identify where there are significant sources of greenhouse gases. They discussed how this can drive accountability and force companies, organisations and nations to take responsibility. 
“Having global data from satellites will give a consistent world daily view which can be fed back to the people that make decisions and push mitigation efforts,” Bram Maasakkers, a senior scientist at the SRON Netherlands Institute for Space Research, explained. 
They also highlighted where there are still crucial gaps in greenhouse gas monitoring, for example of forests and agriculture. Considering some natural ecosystems have been shown to switch from being carbon sinks to sources, accurate measurements can prove how much industries and nations need to reduce their emissions even more to pick up the slack. 
“The drops in carbon absorption by natural sinks are not taken into account in national models which rely on forests to meet their commitments,” explained Oksana Tarasova, a senior scientific officer at the World Meteorological Organisation
Greenhouse gas (GHG) monitoring is now able to give us a detailed picture of where emissions come from in many parts of the world. It can accurately detect tiny amounts: carbon dioxide in the hundreds of parts per million, methane in thousands of parts per billion, nitrous oxide in the hundreds of parts per billion and fluorinated hydrocarbons at even lower levels.
The Copernicus Atmosphere Monitoring Service (CAMS) is one of the leading institutions monitoring levels of carbon dioxide and methane in the atmosphere. Deputy director Richard Engelen explained that it does so by using instruments on the ground, in the air and onboard satellites. The service also uses computer systems to simulate concentrations of the two greenhouse gases based on its knowledge of the atmosphere, biosphere and reported emissions.
It is also possible to accurately measure the emissions from events like wildfires. Engelen took us through a graph of Canadian wildfires where emissions were calculated by detecting the heat emitted with satellites or measuring the burn scars. Scientists then estimate the density of trees that have burnt in a given area.  
Bram Maasakkers, a senior scientist at the SRON Netherlands Institute for Space Research, also explained how the TROPOspheric Monitoring Instrument (TROPOMI) on board the Copernicus Sentinel-5 Precursor satellite creates daily global maps of atmospheric gases including methane, nitrogen dioxide and sulphur dioxide. 
This novel technology can precisely identify emitters by combining TROPOMI data with high-resolution satellite imagery of the earth. “We can detect big methane plumes at levels like 100 tonnes per hour and their sources, such as coal mining in China or oil and gas industries in the US,” Maasakkers explained. “We can pinpoint to an accuracy of about 20 metres.”
The key purpose of being able to identify and measure GHG sources is to bring about accountability as part of the push for net zero. When countries and companies use a bottom-up approach, it involves measuring two key variables: the rate at which an activity tends to produce GHG emissions and the duration of the activity. 
The problem with this system is that unexpected leaks and other irregular releases of GHGs from things like appliances or pipelines are not accounted for. These so-called fugitive emissions made up 5.3 per cent of global GHG emissions in 2013, according to one study. 
A ‘typical’ amount of leakage is now usually factored into emissions inventories, but scientists have found that they are still a considerable underestimation of the problem. This is where the TROPOMI findings can be very significant for mitigation potential. 
“If these are leaks that weren’t known before, this is really important,” Maasakkers said. “We collaborate with the International Methane Emissions Observatory (IMEO) which has a methane alert response system and communicates those leaks to responsible governments and companies so they can be acted upon.”
Engelen added that being able to pinpoint emissions sources facilitates consistency checking of nations’ reported data – which is required annually by the UN. “Having global data from satellites will give a consistent world daily view which can be fed back to the people that make decisions and push mitigation efforts,” he said. 
Scientific data is also the basis for establishing accountability. Amir Sokolowski is the global director of the Climate Change Team at CDP, a not-for-profit charity that runs the global disclosure system for investors, companies, cities, states and regions to manage their environmental impacts.
“We need this information for the next step of who has the responsibility to solve the emissions problem. This way action becomes enforceable,” he said. The CDP has a scoring system for corporations and entities that assesses actions taken to curb emissions. “Science can attribute the source of GHG emissions and then check the impact of the actions that have been taken towards reduction,” he said.
GHG monitoring is also crucial to understanding the role of natural ecosystems as sources or sinks. The world’s natural carbon sinks absorb about half of all human emissions. But recent research by scientists found that in 2023, the hottest year on record, forests, plants and soil absorbed almost no carbon. During the debate, Oksana Tarasova, a senior scientific officer at the World Meteorological Organisation, took us through a graph which shows how much CO2 was not absorbed by plants and trees in Europe during the heatwave of 2022 compared to normal levels. 
In addition, this year the US nonprofit Amazon Conservation used satellite data to calculate how much carbon the Amazon forest stores. Researchers concluded that the effect of deforestation could mean the Amazon will start contributing more carbon than it absorbs from the atmosphere.
Many nations and companies rely on natural carbon sinks to offset their GHG emissions. Having the data to show how much less CO2 they are now absorbing means being able to give a figure to how much more human-generated emissions need to be curbed. Monitoring of natural sinks and sources is the biggest data gap at the moment, and our panellists emphasised the importance of improving its accuracy.
“The drops in carbon absorption by natural sinks are not taken into account in national models which rely on forests to meet their commitments,” explained Tarasova. “In fact, they rely on increased uptake by forests but as we have seen, if we have droughts or wildfires and this does not happen, the national commitments are no longer reliable.”
Tarasova pointed out that companies and organisations can also buy carbon credits from the Amazon and other forests, despite their fluctuating absorption levels. 
The goal of GHG monitoring now is to keep expanding the areas where data is gathered so that the picture can become increasingly more accurate with a longer-term perspective.
This includes improving coverage of the oceans, which are one of the least monitored areas. “This is important because we assume that a significant part of our fossil fuel emissions is being absorbed by the marine environment and if this changes we need to be aware,” explained Engelen. 
“In the meantime, we need to take precautionary actions as there is always going to be a lag between receiving scientific data and being able to respond with mitigation actions,” said Sokolowski. “The most important role of science is to find the strongest link between social accountability and the actions that need to be taken.”
Richard Engelen is a member of the Senior Management Team of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Deputy Director of the Copernicus Atmosphere Monitoring Service, which ECMWF operates on behalf of the European Union.
Engelen is a scientific expert in remote sensing and data assimilation of atmospheric composition with a special focus on the carbon cycle. He is (co-)author of around 50 international peer-reviewed publications in the scientific literature as well as many contributions to conference and workshop proceedings.
He is or has been a member of the Science Advisory Boards of several European projects and a member of expert panels for the European Commission as well as of various proposal review committees in the USA and in the Netherlands.
J.D. (Bram) Maasakkers is a scientist at SRON Netherlands Institute for Space Research. His work focuses on better understanding anthropogenic methane and carbon monoxide emissions using observations of atmospheric concentrations from satellites.
Maasakkers was a summer intern at Harvard as part of the Atmospheric Chemistry Modeling Group, which uses advanced atmospheric chemistry models to understand the atmosphere’s chemical composition, how it is changed by human activity, and what that means for life on Earth. He then joined the research group full-time as a PhD candidate in environmental science and engineering in 2013. 
Dr Oksana Tarasova has worked at the World Meteorological Organisation since 2009. She has been a Senior Scientific Officer in the Infrastructure Department since August 2022 working on the development of the Global Greenhouse Gas Monitoring Infrastructure. 
She was the Head of the Atmospheric Environment Research Division in the Science and Innovation Department from 2014 to 2022 and has a background in Physics and a PhD in Atmosphere Physics.  
The main focus of Tarasova’s activities is international cooperation in observations and analysis of atmospheric composition, with specific expertise in the areas of greenhouse gases. She is currently a member of multiple advisory boards and research projects. She is an author and co-author of over 100 publications.
Amir Sokolowski is the Global Director of the Climate Change Team at CDP, a not-for-profit charity that runs the global disclosure system for investors, companies, cities, states and regions to manage their environmental impacts.
His team provides the strategic direction, helping ensure that CDP incentivises ambition and is in line with the latest knowledge and developments on the subject. Sokolowski has 16 years of experience working on the ground, with governments and as part of international negotiations enhancing every element of climate governance. 
He has worked across many countries drafting legislation, verifying REDD+ (Reducing Emissions from Deforestation and Forest Degradation) projects, negotiating institutions around carbon markets and contributing to the Paris Rule Book.  
Sokolowski has an MPhil from the University of Oxford, specialising in environmental law, and a BA in Medieval History from Tel Aviv University.