We are living through an unprecedented climate and environmental emergency, a fact which has become the defining feature of our time. Political momentum for addressing the human impact on the Earth’s climate and environment has never been higher. Globally, all eyes are on the Paris Agreement and its implementation – particularly now that the United States has re-joined the treaty, and the EU has launched a far-reaching set of policies and actions in the form of the European Green Deal. These developments represent some of the most ambitious political efforts to address the problem of global climate change in our history.
At the heart of these policies is a focus on reducing the net emissions of “greenhouse gases (GHGs)”, which are the primary cause of global warming.
The main greenhouses gases are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3). Some of these gases can remain in the atmosphere for many years, such as CO2; others, like methane, decompose within around 12 years. These gases absorb and re-emit radiant energy, producing the greenhouse effect, which becomes more pronounced the greater the quantity of these gases in the atmosphere.
This article takes a look at the challenges of monitoring greenhouses gases, and how Earth Observation technologies can play a role in this respect.
Taking stock of greenhouse gases: confronting uncertainty
Parties to the UNFCC, the Paris Agreement and the Kyoto protocol are required to produce national greenhouse gas emissions inventories. These are effectively an accounting of sources of emissions, and also include emission removal or sequestration (“sinks”). The European Union compiles a combined inventory for all its Member States, as well as for Iceland and the UK (during the second commitment period of the Kyoto Protocol: 2013-2020). Each country provides a national inventory, based on a common set of methodologies and procedures.
A great deal of effort has been put into establishing good practices and guidelines for the production of comparable and accurate national emissions inventories. Illustratively, the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories is presented in five volumes and runs to several hundred pages. Despite this formidable complexity, the accounting for GHG sources is carried out using a relatively simple approach: emissions are calculated on the basis of activities (such as electricity generation) multiplied by the emissions factor corresponding to the activity. This approach, whilst allowing the production of fairly homogeneous datasets, necessarily generates uncertainty.
The maturity of global emissions inventories in highly variable, and the overall uncertainty is increasing. Countries with less mature or established emissions inventory systems contribute more to global emissions than those with well-established processes and less uncertainty in their inventories.
In the EU, uncertainty of emissions inventories is relatively small (in the order of 3-6%). But, at sub-national scale, uncertainty in emission inventories is much higher, particularly when they are spatially or temporally disaggregated.
The complexity of producing emissions inventories is bound to increase over time, due to factors like the increased use of biofuels (which are currently accounted for as being carbon-neutral, over which there is an ongoing debate) and the future mitigation contributions of the land-use, land-use change, and forestry (LULUCF) sector.
Observing GHGs from space
The use of satellite observations to monitor emissions and GHGs is by no means new, but it is also fairly recent in the history of Earth Observation. The first instrument monitoring carbon dioxide was flown in 1996, and the first satellite dedicated to monitoring greenhouse gases (the Japanese Greenhouse Gases Observing Satellite, GOSAT) was launched in 2009.
The European Space Agency (ESA) has been developing longer-term archives (30+ years) of climate datasets since 2009 as part of its Climate Change Initiative (CCI) programme. Merging data from multiple archives with ongoing satellite missions such as the ESA Earth Explorers, the Copernicus Sentinel constellation and third-parties, the programme generates global datasets for the Essential Climate Variables (ECVs). The programme is structured into 26 thematic projects, each focusing on a field of interest such as Soil Moisture, Biomass or Sea Surface Temperature, one of which is focused on Greenhouse Gases. ESA provides dedicated software (Cate Toolbox) for ingesting, operating on and visualising all ESA Climate Change Initiative (CCI) data.
In its previous incarnation (Greenhouse Gas CCI, 2010-2018), this project produced satellite-derived datasets for CO2 and CH4 from the satellite sensors SCIAMACHY/ENVISAT, GOSAT, and IASI, which are now available via the Copernicus Climate Data Store. The current project (Greenhouse Gas CCI+) is focusing on developing new products (XCO2 and XCH4) using data from a range of missions, including OCO-2, GOSAT-2 and the Sentinel 5 Precursor. A recent procurement notice suggests that ESA intends to further develop capabilities for evaluating emission estimates for methane and other GHGs using current and future satellite missions.
The EU, as part of its Copernicus programme, is launching a dedicated satellite mission for monitoring atmospheric CO2: the Copernicus Carbon Dioxide Monitoring mission (CO2M). Scheduled for launch in 2025, the mission aims to track atmospheric carbon dioxide at a 2km by 2km resolution, across a minimum swath of 250km. This mission was originally designed as a constellation of three satellites, but as of this writing, only two have been contracted.
The launch of this mission is part of a broader EU effort to establish an operational monitoring and verification support capacity of anthropogenic CO₂ emissions. In this respect, two key research projects have advanced the state of the art and laid the groundwork for the future operational system:
- The CO2 Human Emissions (CHE) project is bringing together relevant expertise to develop the science and to scope out the necessary architecture for a European CO2 monitoring capacity. It aims to identify the complementarity between observations, modelling and data assimilation methodologies by establishing their limitations and strengths.
- The VERIFY project is developing scientifically robust methods to assess the accuracy and potential biases in national inventories through an independent pre-operational framework.
The 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories makes special mention of space-based observations, in the context of quality assurance and control. It refers to advancements in “inverse modelling”, an approach which starts with observations of atmospheric concentrations (e.g. from satellites, although other monitoring systems are also used) and uses atmospheric transport and chemistry models to ‘work backwards’ to identify emission sources. Some countries already include inverse modelling outputs in their national inventory reports. Despite the evident potential for this technique, it is itself limited by factors such as uncertainty in the models used. Nonetheless, the document refers the future potential of satellite observations to support this, and other activities supporting the verification of GHG inventories (such as mapping of emission hot spots), as more missions come online.
A role for the private sector?
Although most of the activity carried out in support of GHG emissions monitoring is done at an institutional, governmental or supranational level, there are some private-sector actors carving a niche for commercial provision of services in this area.
GHGSat is a Canadian company monitoring greenhouse gases (GHG), air quality gases, and other trace gas emissions via satellite remote sensing. The company just launched the third satellite in their constellation on a SpaceX Falcon 9 Rideshare, complementing a demonstration satellite launched in 2016 and an operational model launched in 2020. They claim to be able to detect and measure methane emissions from point sources 100x smaller than any comparable system with 100x higher resolution, which is something no other commercial operator or state-funded space organisation can do.
Bluefield carries out monitoring of methane emissions through the combination of multiple satellite sensor data and ground-based sensor measurements. The company offers this product in the context of Environmental, Social, and Governance (ESG) data provision.
WattTime is also monitoring emissions, purportedly at power-plant level, and selling access to their datasets. Besides its commercial activities, WattTime is one of the founding member of Climate TRACE, a global coalition working together to monitor nearly all human-caused GHG emissions worldwide independently and in real time.
Another emerging market is found in the area of carbon offsetting. Pachama, for example, is setting up a service to verify carbon offset though reforestation, and Single Earth is operating a tokenisation system whereby landowners can effectively sell the carbon offset potential of their unused land.
The political pressure from the Paris Agreement in the face of the unfolding climate emergency has spurred governments to act, whilst the monitoring of GHGs from space remains largely an institutional and scientific endeavour, some companies have developed market entry points in specific areas. New missions will bring fresh challenges (e.g. in terms of retrieval algorithms) but, on the positive side, the remaining wide gaps in the adoption of these technologies at national level could lead to greater opportunities for commercial activity in this area.