Scientists have developed new methods for comparing national greenhouse gas inventories with independent measurements collected from space, according to new research published in Earth System Science Data.
With the new approach, scientists combine satellite data of atmospheric carbon dioxide and methane with a model that accounts for the movement or “flux” of these greenhouse gases between the land surface and the atmosphere.
This “inversion method” allows scientists to calculate greenhouse gas emitted into the atmosphere by certain high-emitting countries, as well as the overall flux of carbon dioxide over managed land.
They found out that there were significant differences between these inversion values and the national reports.
The inversion method revealed that methane emissions were higher than the amount most countries reported. Emissions from oil and gas extracting countries in Central Asia and the Gulf, in particular, were several times higher than officially recorded.
In addition, the global land carbon sink, which includes ecosystems on both managed and unmanaged land, absorbs 1.4 billion tonnes of carbon dioxide per year. The observed size was several times bigger than the 0.3 billion tonnes of carbon calculated from countries’ reports.
Underreporting of this carbon sink was most noticeable in temperate and northern hemisphere countries like Canada, as well as throughout the European Union. The gap can be explained by the carbon accumulated by unmanaged ecosystems that lie outside the inventory reporting methodology.
There are some limits to the current criteria for compiling national greenhouse gas inventories. They are frequently based on scaled-up, sector-specific activity and fixed emission factors, for example. As a result, large emission sources, such as those from unmanaged land, are excluded from consideration. More importantly, governments are only urged to check inventories against independently observed measures, not compelled to do so.
The new inversion method, on the other hand, uses satellite data with in-situ measurements to provide a complete picture of emissions that build up in the atmosphere.