www.akademiya2063.org Comprehensive Action Climate Change Initiative (CACCI) Rwanda Knowledge Seminar – March 2024 Racine Ly, Ph.D., Director, Department Data Management, Digital Products and Technology, AKADEMIYA2063 Mansour Dia, Associate Scientist, AKADEMIYA2063 Dakar, Senegal – March 26th, 2024

www.akademiya2063.org Summary 1. Justifying Methane tracking 2. Data and Methodology 3. Results for Rwanda 4. Discussions and next steps

1. Justifying Methane Tracking • Most climate change mitigation and adaptation discussions have focused on carbon dioxide. Recently, methane emissions reduction has attracted substantial attention as a more effective strategy to mitigate global warming. • That is due to its capacity to absorb and re-emit infrared radiation (heat) and its relatively short lifetime in the atmosphere of around 12 years. • The removal of 1 ton of Methane corresponds to around 84 to 86 tons of CO2 removals over 20 years and 28 to 34(1) tons over 100 years (2) (IPCC, 2023). (1) A global warming potential of 21 is often accepted for methane since the second IPCC assessment in 1995. However, due to a better understanding of methane indirect effect on climate forcing, a global warming potential of 25 have been proposed since the fourth assessment in 2007 factoring in the enhancement of tropospheric ozone, stratospheric water vapor and production of CO2 resulting from methane destruction in the atmosphere. The latest IPCC assessment reviewed the Methane global warming potential to between 28 to 36 during its last assessment. (2) The methane global warming potentials provided here, have been retrieved from the IPCC Fifth assessment report Global Warming Potentials (GWP) AR5 in 2014. In 2021, the sixth assessment report provide close figures of methane GWP but with a distinction of fossil and non-fossil methane origin. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 3

• When investigating the global methane budget, it appears that a wide range of natural and anthropogenic sources are balanced with few, often radiative reinforcing sinks. • The sources are estimated to emit between +500 and +600 Tg(3) CH4 yr-1 on average, while the sinks are estimated to remove between –460 and –580 Tg CH4 yr-1 globally. • Based on the above figures, the global community needs to deal with an exceeding budget of between +20 and +52 Tg CH4 yr-1 only. • However, following such an analysis will be misleading since the impact of rising temperatures on methane emissions is not considered. • Example of positive feedback for Methane: Methane emission depends on temperature, water table depth, and substrate availability; Temperature is often the dominant factor of the three. (3) Read Tera gram which corresponds to 1 million grams 1. Justifying Methane Tracking Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 4

1. Justifying Methane Tracking • In Africa, despite the political will to combat climate change, several barriers impede the effective design and implementation of policies and interventions to combat climate change. • One of the most prominent barriers is the lack of data about the dynamics of greenhouse gas emissions to inform those policies and interventions. • The lack of data makes climate reporting subject to inaccuracies, leading to under or overestimating the budget of greenhouse gases, particularly Methane, in countries. “To get to a 1.5-degree pathway, about a third of the methane emissions should be eliminated from our current levels by 2030 and about 45 percent by 2040.” • Such a drastic reduction requires contributions from all, including Africa, and such a journey should start with a stocktaking exercise of the current level of methane emissions. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 5

2. Data and Methodology • Not all layers of the atmosphere are directly impacted by anthropogenic activities. The troposphere (0 to 10 km above ground is the most affected). • The troposphere is, therefore, the layer with the largest concentration of Greenhouse gases. The layers of Earth's atmosphere, with a yellow line showing the air temperature at various heights. Encyclopædia Britannica, Inc. Earth Atmospheric Layers Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 6

2. Data and Methodology Measuring Trace Gases Atmospheric Abundance Total atmospheric transmission spectra in the 1.6 μm spectral range (upper panel) and the contribution of CO2 absorption (middle panel) and CH4 (lower panel). • On its way through the atmosphere, light gets absorbed by atmospheric trace gases. • The depth of the absorption lines in the reflected spectrum provides information about its atmospheric abundance. • For instance, CH4 and CO2 absorb lights in the 1.6 micrometer spectral range. • The “intensity” of absorptions is the proxy of gases’ abundance. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 7

2. Data and Methodology TROPOMI Measurements Principles TROPOMI measurement principle. The dark-gray ground pixel is imaged on the two- dimensional detector as a spectrum. All ground pixels in the 2600 km wide swath are simultaneously measured (Veefkind et al., 2012) • Data provided by TROPOMI are 3,5 x 7 km2 approximately at NADIR. • TROPOMI is a passive sensor. • S5P covers the entire globe daily. • Weekly averaged data are publicly available. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 8

2. Data and Methodology TROPOMI Methane Data Validation I • The Total Carbon Column Observing Network (TCCON) is used to validate TROPOMI data with ground stations. • TCCON is a network of ground- based Fourier Transform Spectrometers recording direct solar spectra in the near-infrared spectral region. • From these spectra, accurate and precise column-averaged abundance of CO2 , CH4 , N2 O, HF, CO, H2 O, and HDO are retrieved. Lorente, A., Borsdorff, T., Butz, A., Hasekamp, O., aan de Brugh, J., Schneider, A., Wu, L., Hase, F., Kivi, R., Wunch, D., Pollard, D. F., Shiomi, K., Deutscher, N. M., Velazco, V. A., Roehl, C. M., Wennberg, P. O., Warneke, T., and Landgraf, J.: Methane retrieved from TROPOMI: improvement of the data product and validation of the first 2 years of measurements, Atmos. Meas. Tech., 14, 665–684, https://doi.org/10.5194/amt-14-665-2021, 2021 Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 9

2. Data and Methodology TROPOMI Methane Data Validation II Lorente, A., Borsdorff, T., Butz, A., Hasekamp, O., aan de Brugh, J., Schneider, A., Wu, L., Hase, F., Kivi, R., Wunch, D., Pollard, D. F., Shiomi, K., Deutscher, N. M., Velazco, V. A., Roehl, C. M., Wennberg, P. O., Warneke, T., and Landgraf, J.: Methane retrieved from TROPOMI: improvement of the data product and validation of the first 2 years of measurements, Atmos. Meas. Tech., 14, 665–684, https://doi.org/10.5194/amt-14-665-2021, 2021 Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 10

3. Results for Rwanda Rwanda Methane Concentration Overview over Croplands • In Rwanda, the maximum of methane concentration occurs in the northern part of the country. • The Minimum of methane concentration occurs in the southern part of the country. • The normal range of concentration remains to be established. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 11

3. Results for Rwanda Rwanda Methane Concentration over Beans Fields Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 12

3. Results for Rwanda Rwanda Methane Concentration over Maize and Sorghum Fields Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 13

3. Results for Rwanda Rwanda Methane Concentration over croplands – 2022 long rainy season (Mar – May) The Northern part of the country shows a higher concentration of methane independently of the crop growing stages. While the reasons for that are unknown to us. Further investigation will be performed with colleagues to append explainability to the observations. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 14

3. Results for Rwanda Rwanda Methane Concentration over croplands – 2022 short rainy season (Sep – Nov) The Northern part of the country shows a higher concentration of methane independently of the crop growing stages. However, the southern part shifted to higher concentration levels during the 2022 short rainy season growing period. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 15

3. Results for Rwanda Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 Rwanda Methane Concentration over croplands – short (Dec – Feb) and long (Jun – Aug) dry seasons 16

4. Conclusions and Perspectives • The TROPOMI data allows us to establish a baseline of methane concentrations above several land use and land covers in the country and through time. • The time series analysis allows the learn better the interrelationships between concentration changes with land management practices and climate parameters’ anomalies. Such would allow a better assessment of policies’ impacts. • As a way forward, the team will further investigate the methane dynamics above other land use and land covers and against temperature and rainfall anomalies. • New methane emission datasets with source allocation capabilities are expected to be released by the end of 2024. The team is getting ready for their acquisition and processing for Rwanda. Dr. Racine Ly and Mansour Dia – CACCI Knowledge Seminar Rwanda – March 26th, 2024 17

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