Tomorrow, NASA launches the OCO-2 satellite, which will make a detailed map of how much CO2 is in the atmosphere at various points on the globe. They plan to combine that data with data from other existing satellites, atmospheric sampling, and ground sampling, with the goal of finding out where CO2 is being produced and where it's being absorbed—in very high resolution, about 3 km2 per measurement, or, smaller than a big coal-fired power plant.
The satellite will be in a polar orbit which allows it to fly over every single spot on earth every 16 days, which means it will generate a complete map of CO2 concentrations every 16 days—less the areas that were covered in cloud when it flew over on that cycle. This repeated mapping also means that seasonal variations can be tracked, to separate a long-term trend from a seasonal fluctuation.
OCO-2 measures CO2 by measuring how much light is absorbed by the CO2 as sunlight travels down to the surface, reflects off the planet, and bounces back up to the satellite. So, cloud cover interferes with the measurement, and repeated mapping is one of the ways they're compensating for that.