I read here that volcanoes release about "0.6 billion metric tons of carbon dioxide per year". I wonder though, how scientists can estimate the emissions from large regions with geological features that release carbon dioxide and methane. For example, here in the Czech Republic, we have countless springs with carbonated water. Some have only a few bubbles while others shoot out like a freshly opened bottle of sparkling wine. Since the Czech republic has an area of 78 870km² it seems impossible that geologists could ever count and measure the output from all these springs, especially since the vast majority of them probably seep their carbon into underground caves, which then leak into the surface soil and eventually the atmosphere. It seems to me, that there is probably carbon seeping into the atmosphere from every m² of land in the country, and at wildly varying rates. What kind of methods to geologist use to get even a rough estimate? Do they try like covering the ground with 100m² tarps and try gathering the carbon that comes up? I'm just guessing here...
Tracking atmospheric species over the entire planet really is comparatively easy via satellites, compared to plastering entire swathes of land with measurement stations.
You make one infrared image from an imaging satellite at the right wavelength and you got the entire country covered. The right wavelength to choose has to be
- originating from the molecule in emission at the right altitude and
- be optically thin. If you know your emission is optically thin, the flux in your image is directly proportional to the mass that is emitting this flux. If it's not optically thin, complications apply, but the idea is the same.
An example of the observational fleet that NASA has in orbit can be found here (scroll down the page). There it also becomes clear, that various instruments are needed to cover the entire range of interesting atmospheric species, which necessitates a number of observation platforms/satellites.