Both the Japanese and American Space agencies, JAXA and NASA, are about to launch satellites into orbit which measure Earth's carbon dioxide and methane levels, hoping to glean insight into global warming's effects.
According to the Economist, the Japanese satellite, Ibuki, will circle the Earth every 100 minutes, collecting data from 56,000 points around the world at 667km above the surface. For detection methods, it uses a spectrometer to detect carbon dioxide and methane levels through the sun, and can detect changes down to one part per million. Ibuki also uses a detector which reads clouds and aerosols for radiation levels.
The American satellite, the Orbiting Carbon Observatory, will circle the Earth every 99 minutes (take THAT, Japan!), and fly at an altitude of 724km. OCO will use three spectrometers to measure carbon dioxide and oxygen levels, and report back with concentration maps every 16 days.
The goal with these satellites is two fold: first, it will hopefully help figure out what happens to CO2 after it is produced. Scientists think there is a large "sink" of unaccounted-for greenhouse gases some where on the planet, but there's no definitive proof of where that might be. Secondly, they want to figure out the effect that natural CO2 producers, such as rain forests and forest fires, have on the planet. Though they can measure man-made CO2 levels using more accurate ground sensors, figuring out what role the natural world plays in all this has been difficult. Maybe this will answer the question. [Economist]