A fridge-sized satellite spies on the world’s carbon emissions, now we know just how much 100 nations are producing

High above the Earth, a satellite has been spying on global carbon emissions and now NASA has used the data to release a study that estimates the mass of carbon emitted and removed by the majority of the world’s nations.

Named OCO-2, the satellite has been orbiting the planet’s two poles for a decade, with an instrument containing three spectrometers pointed at the planet below.

These spectrometers measure the intensity of sunlight reflected by carbon dioxide in the atmosphere using a diffraction grating – not unlike the colourful reflection visible on the back of a CD – to split the sunlight hitting the instrument into its component colours.

The small wavelengths that bounce off weak and strong CO₂, and oxygen, are then precisely detected by the finely tuned spectrometers to determine the presence of these gases in the atmosphere.

The OCO-2 monitors how the composition of gases in the atmosphere change over time by taking repeated measurements when passing specific locations on the planet’s surface once every 16 days.

Taking ‘top-down’ measurements from satellites like OCO-2 is particularly helpful for nations which lack the resources to effectively monitor carbon output at ground level.

The other way is to use ground-based instruments to measure carbon from the bottom-up, but this requires nations to estimate and assess each part of their economy to determine how much they emit.

Bottom-up measurements are very detailed, but are time-intensive and costly. Still, these comprehensive measurements are supported by space-based observations, which give another layer of high-resolution verification to carbon assessments.

Among the data obtained by the OCO-2 project, researchers not only mapped increase in atmospheric carbon concentrations, but shifts in the amount of carbon stored in ecosystems.

These carbon ‘stocks’ are vital for efforts to reduce carbon concentrations, with plants, soils and oceans particularly important in capturing and storing carbon and preventing it from reaching the atmosphere.

Maps provided by the researchers show how changes in land management influence carbon emissions. In nations like the US, Canada and parts of Europe, improvements in land care extract and store carbon, whereas deforestation in nations like Brazil and Australia can be seen to have a negative effect on carbon stocks.

Carrying the burden of the world’s carbon shifts are so-called unmanaged ecosystems – areas of the world which are largely untouched by human impacts. Space-based monitoring like that carried out by OCO-2 can be useful in compensating for lower levels of human monitoring in these locations to check for changes in the amount of carbon they sequester.

“National inventories are intended to track how management policies impact emissions and removals of CO₂,” says Professor Noel Cressie from the University of Wollongong, one of the over 60 scientists involved in the project.

“However, the atmosphere doesn’t care whether CO₂ is being emitted from deforestation in the Amazon or wildfires in the Canadian Arctic. Both processes will increase the concentration of atmospheric CO₂ and drive climate change.

“Therefore, it is critical to monitor the carbon balance of unmanaged ecosystems and identify any changes in carbon uptake.”

The published OCO-2 measurements may be used to inform the upcoming global carbon stocktake, which will be held in Dubai during November and December this year.