Southeast Australia experienced intensive and geographically extensive wildfires during the 2019-2020 summer season. The fires released substantial amounts of carbon dioxide into the atmosphere. ...However, existing emission estimates based on fire inventories are uncertain, and vary by up to a factor of four for this event. Here we constrain emission estimates with the help of satellite observations of carbon monoxide, an analytical Bayesian inversion and observed ratios between emitted carbon dioxide and carbon monoxide. We estimate emissions of carbon dioxide to be 715 teragrams (range 517-867) from November 2019 to January 2020. This is more than twice the estimate derived by five different fire inventories, and broadly consistent with estimates based on a bottom-up bootstrap analysis ofthis fire episode. Although fires occur regularly in the savannas in northern Australia, the recent episodes were extremely large in scale and intensity, burning unusually large areas of eucalyptus forest in the southeast. The fires were driven partly by climate change, making better-constrained emission estimates particularly important. This is because the build-up of atmospheric carbon dioxide may become increasingly dependent on fire-driven climate-carbon feedbacks, as highlighted by this event.
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GEOZS, IJS, IMTLJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK, ZAGLJ
Methane emissions due to accidents in the oil and natural gas sector are very challenging to monitor, and hence are seldom considered in emission inventories and reporting. One of the main reasons is ...the lack of measurements during such events. Here we report the detection of large methane emissions from a gas well blowout in Ohio during February to March 2018 in the total column methane measurements from the spaceborne Tropospheric Monitoring Instrument (TROPOMI). From these data, we derive a methane emission rate of 120 ± 32 metric tons per hour. This hourly emission rate is twice that of the widely reported Aliso Canyon event in California in 2015. Assuming the detected emission represents the average rate for the 20-d blowout period, we find the total methane emission from the well blowout is comparable to one-quarter of the entire state of Ohio’s reported annual oil and natural gas methane emission, or, alternatively, a substantial fraction of the annual anthropogenic methane emissions from several European countries. Our work demonstrates the strength and effectiveness of routine satellite measurements in detecting and quantifying greenhouse gas emission from unpredictable events. In this specific case, the magnitude of a relatively unknown yet extremely large accidental leakage was revealed using measurements of TROPOMI in its routine global survey, providing quantitative assessment of associated methane emissions.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
This work presents the operational methane retrieval algorithm for the Sentinel 5 Precursor (S5P) satellite and its performance tested on realistic ensembles of simulated measurements. The target ...product is the column-averaged dry air volume mixing ratio of methane (XCH4), which will be retrieved simultaneously with scattering properties of the atmosphere. The algorithm attempts to fit spectra observed by the shortwave and near-infrared channels of the TROPOspheric Monitoring Instrument (TROPOMI) spectrometer aboard S5P.The sensitivity of the retrieval performance to atmospheric scattering properties, atmospheric input data and instrument calibration errors is evaluated. In addition, we investigate the effect of inhomogeneous slit illumination on the instrument spectral response function. Finally, we discuss the cloud filters to be used operationally and as backup.We show that the required accuracy and precision of < 1 % for the XCH4 product are met for clear-sky measurements over land surfaces and after appropriate filtering of difficult scenes. The algorithm is very stable, having a convergence rate of 99 %. The forward model error is less than 1 % for about 95 % of the valid retrievals. Model errors in the input profile of water do not influence the retrieval outcome noticeably. The methane product is expected to meet the requirements if errors in input profiles of pressure and temperature remain below 0.3 % and 2 K, respectively. We further find that, of all instrument calibration errors investigated here, our retrievals are the most sensitive to an error in the instrument spectral response function of the shortwave infrared channel.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
We use atmospheric observations to quantify methane (CH4) emissions from Mexico's most important onshore and offshore oil and gas production regions which account for 95% of oil production and 78% of ...gas production. We use aircraft-based top-down measurements at the regional and facility-levels to determine emissions. Satellite data (TROPOMI CH4 data and VIIRS night-time flare data) provide independent estimates of emissions over 2 years. Our airborne estimate of the offshore region's emissions is 2800 kg CH4 h−1 (95% confidence interval (CI): 1700-3900 kg CH4 h−1), more than an order of magnitude lower than the Mexican national greenhouse gas inventory estimate. In contrast, emissions from the onshore study region are 29 000 kg CH4 h−1 (95% CI: 19 000-39 000 kg CH4 h−1), more than an order of magnitude higher than the inventory. One single facility-a gas processing complex that receives offshore associated gas-emits 5700 kg CH4 h−1 (CI: 3500-7900 kg CH4 h−1), with the majority of those emissions related to inefficient flaring and representing as much as half of Mexico's residential gas consumption. This facility was responsible for greater emissions than the entirety of the largest offshore production region, suggesting that offshore-produced associated gas is being transported onshore where it is burned and in the process some released to the atmosphere. The satellite-based data suggest even higher emissions for the onshore region than did the temporally constrained aircraft data (>20 times higher than the inventory). If the onshore production region examined is representative of Mexican production generally, then total CH4 emissions from Mexico's oil and gas production would be similar to, or higher than, the official inventory, despite the large overestimate of offshore emissions. The main driver of inaccuracies in the inventory is the use of generic, non-Mexican specific emission factors. Our work highlights the need for local empirical characterization of emissions if effective emissions mitigation is to be undertaken.
The hydrological cycle and its response to environmental variability such as temperature changes is of prime importance for climate reconstruction and prediction. We retrieved deuterated water/water ...(HDO/H2O) abundances using spaceborne absorption spectroscopy, providing an almost global perspective on the near-surface distribution of water vapor isotopologs. We observed an unexpectedly high HDO/H2O seasonality in the inner Sahel region, pointing to a strong isotopic depletion in the subsiding branch of the Hadley circulation and its misrepresentation in general circulation models. An extension of the analysis at high latitudes using ground-based observations of deltaD and a model study shows that dynamic processes can entirely compensate for temperature effects on the isotopic composition of precipitation.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
We quantify the impact of atmospheric transport and limited marine boundary layer sampling on changes in global and regional methane burdens estimate using tracer transport model simulations with ...annually repeating methane emissions and sinks but varying atmospheric transport patterns. We find the 1σ error due to this transport and sampling effect on annual global methane increases to be 1.11 ppb/year and on zonal growth rates to be 3.8 ppb/year, indicating that it becomes more critical at smaller spatiotemporal scales. We also find that the trends in inter‐hemispheric and inter‐polar difference of methane are significantly influenced by the effect. Contrary to a negligible trend in the inter‐hemispheric difference of measurements, we find, after adjusting for the transport and sampling, a trend of 0.37 ± 0.06 ppb/year. This is consistent with the emission trend from a 3‐D inversion of the measurements, suggesting a faster increase in emissions in the Northern Hemisphere than in the Southern Hemisphere.
Plain Language Summary
Changes in global and regional atmospheric burdens of methane are determined by the net effect of sources and sinks and atmospheric transport. Many studies approximate the burdens based on measurements from a network of globally distributed surface air sampling sites. Here we quantify the impact of atmospheric transport and limited marine boundary layer sampling (transport and sampling) on changes in global and regional methane burden estimates using tracer transport model simulation with annually repeating methane emissions and sinks but varying atmospheric transport patterns. We find that for assessing the annual global methane increases, a measurement‐only approach is fairly accurate. However, extending the measurement‐only analysis to hemispheric or latitudinal variations is more problematic as transport influences quickly become significant or even dominant. We find a large impact of transport and sampling effect on the inter‐hemispheric and inter‐polar difference.
Key Points
Transport gives rise to CH4 variations in the spatiotemporal gradients, which are not caused by source or sink changes
We find the transport and sampling error on annual global CH4 increases to be 1.11 ppb/year and on zonal growth rates to be 3.8 ppb/year
The transport‐adjusted inter‐hemispheric difference has a trend of 0.37 ppb/year, consistent with the emission trend from a 3‐D inversion
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Methane retrievals from near‐infrared spectra recorded by the SCIAMACHY instrument onboard ENVISAT hitherto suggested unexpectedly large tropical emissions. Even though recent studies confirm ...substantial tropical emissions, there were indications for an unresolved error in the satellite retrievals. Here we identify a retrieval error related to inaccuracies in water vapor spectroscopic parameters, causing a substantial overestimation of methane correlated with high water vapor abundances. We report on the overall implications of an update in water spectroscopy on methane retrievals with special focus on the tropics where the impact is largest. The new retrievals are applied in a four‐dimensional variational (4D‐VAR) data assimilation system to derive a first estimate of the impact on tropical CH4 sources. Compared to inversions based on previous SCIAMACHY retrievals, annual tropical emission estimates are reduced from 260 to about 201 Tg CH4 but still remain higher than previously anticipated.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The growth rate of atmospheric carbon dioxide (CO2) reflects the net
effect of emissions and uptake resulting from anthropogenic and natural
carbon sources and sinks. Annual mean CO2 growth rates ...have been
determined from satellite retrievals of column-averaged dry-air mole fractions
of CO2, i.e. XCO2, for the years 2003 to 2016. The XCO2
growth rates agree with National Oceanic and Atmospheric Administration
(NOAA) growth rates from CO2 surface observations within the uncertainty
of the satellite-derived growth rates (mean difference ± standard
deviation: 0.0±0.3 ppm year−1; R: 0.82). This new and independent data
set confirms record-large growth rates of around 3 ppm year−1
in 2015 and 2016, which are attributed to the 2015–2016 El Niño. Based on a comparison of
the satellite-derived growth rates with human CO2 emissions from fossil
fuel combustion and with El Niño Southern Oscillation (ENSO) indices, we
estimate by how much the impact of ENSO dominates the impact of fossil-fuel-burning-related emissions in explaining the variance of the atmospheric
CO2 growth rate. Our analysis shows that the ENSO impact on CO2
growth rate variations dominates that of human emissions throughout the
period 2003–2016 but in particular during the period 2010–2016 due to strong
La Niña and El Niño events. Using the derived growth rates and their
uncertainties, we estimate the probability that the impact of ENSO on the
variability is larger than the impact of human emissions to be 63 % for the
time period 2003–2016. If the time period is restricted to 2010–2016, this
probability increases to 94 %.
Year-to-year variations in the atmospheric methane (CH
) growth rate show significant correlation with climatic drivers. The second half of 2010 and the first half of 2011 experienced the strongest ...La Niña since the early 1980s, when global surface networks started monitoring atmospheric CH
mole fractions. We use these surface measurements, retrievals of column-averaged CH
mole fractions from GOSAT, new wetland inundation estimates, and atmospheric δ
C-CH
measurements to estimate the impact of this strong La Niña on the global atmospheric CH
budget. By performing atmospheric inversions, we find evidence of an increase in tropical CH
emissions of ∼6-9 TgCH
yr
during this event. Stable isotope data suggest that biogenic sources are the cause of this emission increase. We find a simultaneous expansion of wetland area, driven by the excess precipitation over the Tropical continents during the La Niña. Two process-based wetland models predict increases in wetland area consistent with observationally-constrained values, but substantially smaller per-area CH
emissions, highlighting the need for improvements in such models. Overall, tropical wetland emissions during the strong La Niña were at least by 5% larger than the long-term mean.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The Measurements of Pollution in the Troposphere (MOPITT) instrument is the only satellite-borne sensor in operation that uses both thermal (TIR) and near-infrared (NIR) channels to estimate CO ...profiles. With more than 15 years (2000 to present) of validated multispectral observations, MOPITT provides the unique capability to separate CO in the lowermost troposphere (LMT, surface to 3 km (∼ 700 hPa)) from the free-tropospheric abundance. To extend this record, a new, hyper-spectral approach is presented here that will provide CO data products exceeding the capabilities of MOPITT by combining the short-wavelength infrared (SWIR, equivalent to the MOPITT NIR) channels from the TROPOspheric Monitoring Instrument (TROPOMI) to be launched aboard the European Sentinel 5 Precursor (S5p) satellite in 2016 and the TIR channels from the Cross-track Infrared Sounder (CrIS) aboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. We apply the MUlti-SpEctra, MUlti-SpEcies, Multi-SEnsors (MUSES) retrieval algorithm to quantify the potential of this joint CO product. CO profiles are retrieved from a single-footprint, full-spectral-resolution CrIS transect over Africa on 27–28 August 2013 coincident with significant biomass burning. Comparisons of collocated CrIS and MOPITT CO observations for the LMT show a mean difference of 2.8 ± 24.9 ppb, which is well within the estimated measurement uncertainty of both sensors. The estimated degrees of freedom (DOF) for CO signals from synergistic CrIS–TROPOMI retrievals are approximately 0.9 in the LMT and 1.3 above the LMT, which indicates that the LMT CO can be distinguished from the free troposphere, similar to MOPITT multispectral observations (0.8 in the LMT, and 1.1 above the LMT). In addition to increased sensitivity, the combined retrievals reduce measurement uncertainty, with ∼ 15 % error reduction in the LMT. With a daily global coverage and a combined spatial footprint of 14 km, the joint CrIS–TROPOMI measurements have the potential to extend and improve upon the MOPITT multispectral CO data records for the coming decade.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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