FAQ (CarbonTracker-CH4)
Q1: I'm a member of the press and would like more information, to whom do I turn?
Q2: Can I use whatever I find on these pages?
Q3: How do I cite or acknowledge CarbonTracker-CH4work?
Q4: What data are available beyond those currently offered through FTP, and how do I get them?
Q5: Why is CarbonTracker-CH4 almost a year behind the current date?
Q6: How reliable are your products?
Q7: Where can I find more technical details on CarbonTracker-CH4?
Q8: I'm having trouble using the CarbonTracker-CH4 results, where can I get help?
Q9: Are CarbonTracker-CH4 results available for earlier releases?
Q10: What are the units of CH4 emissions that CarbonTracker-CH4 uses?
Q11: What are the units of atmospheric CH4 abundance that CarbonTracker-CH4 uses?

Q1: I'm a member of the press and would like more information, to whom do I turn?
A1: Please contact Arlyn Andrews (NOAA GML Carbon Cycle Division Lead) to discuss CarbonTracker CH4, get the latest carbon cycle insights, or obtain additional material.

Q2: Can I use whatever I find on these pages?
A2: Yes, all our results are free to be used by the public, scientists, and others. This includes all figures, numbers, data files, and even source code (upon request). We encourage you to contact us with questions to ensure proper representation of the results, and we welcome any feedback and possibility for cooperation. Please acknowledge the CarbonTracker efforts when you use them in your scientific endeavors.

Q3: How do I cite or acknowledge CarbonTracker-CH4 work?
A3: We ask that scientific work that relies heavily on CarbonTracker products is discussed with us before publication, to ensure proper representation of our work and co-authorship if appropriate. Detailed instructions for acknowledgment are available at our citation page.

Q4: What data are available beyond that currently offered through FTP, and how do I get them?
A4: In addition to the available global fluxes and mole fraction data, we can provide prior data, inferred posterior fluxes for each source sector, and flux uncertainties. Please contact us to discuss the sharing of these results.

Q5: Why is CarbonTracker-CH4 almost a year behind the current date?
A5: CarbonTracker operates with at least a one-year delay. Our next release will update flux estimates through the end of 2022. There are several reasons for this delay, but the most important one is that there is a lag in receiving air sample flasks from around the world, analyzing their contents for CH4 and its stable isotope ratio (δ13C-CH4), and performing the requisite quality control. This process involves many people and many hours of meticulous work. As a result, the CH4 mole fraction data for 2022 won't be available for our CarbonTracker modeling efforts until 2023-2024. Preparing the CarbonTracker-CH4 product itself may require another several months or so of modeling effort.

While CarbonTracker results are lagged by a year, the raw flask and in-situ observations themselves are posted as soon as they are available, even as the quality-control efforts are underway. For the most up-to-date observational data, you can visit our interactive data visualization page at: http://gml.noaa.gov/dv/iadv/.

Q6: How reliable are your products?
A6: The reliability of our products depends on the time and location for which they are assessed. Results that are aggregated in space (e.g., whole continents) or time (e.g., seasonal averages) will be more robust than local or instantaneous estimates. For the fluxes, formal uncertainty estimates of fluxes (full covariance matrices are available upon request) give some indication of the random errors we expect. However, systematic errors (e.g., biases) might dominate these at specific times and locations. Calculated mole fraction data will generally be reliable to within the specified model-data mismatch errors at each site, while mole fractions at other locations will be better constrained in the proximity of assimilated sites. Assessing our products against independent data and quantifying their reliability is an important and ongoing task for the CarbonTracker-CH4 team. We welcome any help and assistance, or feedback you might have on this issue. The CarbonTracker-CH4 team will generally quote conservative formal uncertainty estimates on all website products.

Q7: Where can I find more technical details on CarbonTracker-CH4?
A7: The most complete information about CarbonTracker-CH4 is available on our documentation page. For technical details beyond the documentation page, we suggest you read the literature, visit our collaborators page, see our release notes, or contact us.

Q8: I'm having trouble using the CarbonTracker-CH4 results, where can I get help?
A8: Send us an email describing in detail what you are trying to do, and what problem you run into. We will make every attempt to help you along.

Q9: Are CarbonTracker-CH4 results available for earlier releases?
A9: Yes. Previous versions of CarbonTracker-CH4 have been archived and are available on our versions page.

Q10: What are the units of CH4 emissions that CarbonTracker uses?
A10: CH4 emissions are reported in mass of CH4 released into the atmosphere per unit of time, over some assumed area. We generally report emissions in teragrams of CH4 per year, or TgCH4/yr. A teragram is 1012 g, or 1 million metric tons of CH4.

Q11: What are the units of atmospheric CH4 abundance that CarbonTracker-CH4 uses?
A11: Atmospheric CH4 abundances are reported as a dry-air mole fraction, in parts per billion ("ppb"). This is the ratio of the number of CH4 molecules in the sample to the total number of molecules, excluding water molecules. Parts per billion are equivalent to nanomol/mol (or nmol mol-1), so we sometimes report abundances using that form. This ratio means that for a sample of dry air having a CH4 abundance of 2000 ppb, out of every billion molecules, 2000 are CH4. Historically, abundances were sometimes erroneously reported as parts per billion by volume ("ppbv"), which is only equivalent to ppb if you assume that CH4 and dry air (consisting mostly of N2 and O2 molecules) act as ideal gases. This is not generally true, and as a result the CH4 community now reports dry-air mole fractions as ratios of the number of molecules, not of their volumes.