In 2013, the National Oceanic and Atmospheric Administration (NOAA) reported that atmospheric concentrations of carbon dioxide (CO2) had reached 400 parts per million (ppm) for the first time since the Pliocene Era (ca. 3 million years ago).
According to the IPCC's Sixth Assessment Report (AR6), "excess carbon dioxide" in our atmosphere will result in a global average temperature increase of between 1.5 and 2 °C by 2030.
This will significantly affect ecological systems worldwide, including species extinction, droughts, wildfires, extreme weather, and crop failures.
Aside from curbing emissions, these changes call for mitigation and adaptation strategies and climate monitoring. This is the purpose of NASA's Orbiting Carbon Observatory (OCO) 2 and 3 missions, twin satellites that make space-based observations of CO2 in Earth's atmosphere to understand the characteristics of climate change better.
Using the world's fifth-largest coal-fired power plant as a test case, a team of researchers used data from OCO 2 and 3 to detect and track changes in CO2 and quantify the emissions produced below.
The research was led by Ray Nassar, a senior researcher with Environment and Climate Change Canada (ECCC) and an adjunct professor at the University of Toronto (UofT). He was joined by researchers from ECCC, UofT, Colorado State University, and NASA's Jet Propulsion Laboratory (JPL).
The paper that describes their findings was published on 28 October 2022 in Frontiers in Remote Sensing.
Their findings demonstrate that space-based observations can be used to track CO2 emission changes at a local scale.
Launched in 2014, the OCO-2 satellite maps natural and anthropogenic CO2 emissions on regional and continental scales. This is done indirectly by measuring the intensity of sunlight reflected off Earth's surface and directly by measuring the amount of CO2 absorbed in the column of air between the surface and the satellite.
The OCO-2 satellite also has spectrometers calibrated to detect the specific signature of CO2 gas. Its companion (OCO-3) was built using OCO-2's spare parts and was launched to the International Space Station (ISS) in 2019.
This instrument includes a mapping mode that can make sweeping observations over entire areas, allowing researchers to use OCO-3 to create detailed mini-maps on the scale of major cities – where excess carbon emissions are concentrated.
Using data obtained during multiple overpasses between 2017 and 2022, the research team analyzed the emissions of the largest single-emissions source in Europe – the Belchatów Power Station in Poland.
From this, they detected changes in CO2 levels that were consistent with hourly fluctuations in the plant's electricity production.
The Belchatów Power Station has been in operation since 1988 and will remain open until the end of 2036 (according to the Polish government). It is currently the largest coal-fired power plant in the world (with a reported capacity of 5,102 megawatts).
It uses brown coal (lignite), which typically generates higher emissions per megawatt than hard coal (anthracite). Large facilities, such as power plants and oil refineries, account for about half of the global carbon emissions from fossil fuels.
Neither satellite was originally designed to detect emissions from specific individual facilities such as Belchatów.
In a NASA press release, OCO-3 mission project scientist Abhishek Chatterjee explained how this made their results a "pleasant surprise" and how he and his colleagues look forward to future research opportunities:
"As a community, we are refining the tools and techniques to be able to extract more information from the data than what we had originally planned. We are learning that we can actually understand a lot more about anthropogenic emissions than what we had previously expected. It is really exciting to think that we will get another five to six years of operations with OCO-3. We are seeing that making measurements at the right time and at the right scale is critical."
According to Nasser, most CO2 emissions reports are created from estimates or data collected at Earth's surface level. This consists of accounting for the mass of fossil fuels used, calculating the expected emissions, and generally doesn't involve atmospheric measurements.
Said Nasser: "The finer details about exactly when and where emissions occur are often not available. Providing a more detailed picture of carbon dioxide emissions could help to track the effectiveness of policies to reduce emissions. Our approach with OCO-2 and OCO-3 can be applied to more power plants or modified for carbon dioxide emissions from cities or countries."
In the future, climate scientists will benefit from the mapping mode of observations of OCO-3, which could serve as a "pathfinder" for next-generation satellite missions. NASA recently announced that mission operations with OCO-3 aboard the ISS will be extended for several more years.
The instrument will operate alongside another greenhouse gas observation mission, the Earth Surface Mineral Dust Source Investigation (EMIT).
These and other efforts to monitor climate change and CO2 emissions in real time will prove invaluable to mitigation and adaptation efforts.