 How can we fight climate change if we don't know where greenhouse gases are really coming from? Governments around the world are making serious commitments to reduce their national emissions. But to do that effectively, decision makers need to know the exact amounts and origins of the different gases being released in their region. A cutting-edge scientific technique is now giving governments and industries this data. Scientists are using something called stable isotopes to fingerprint each gas present in a sample of air and trace its source. This allows the authorities to target their climate policies to the biggest polluters and not miss any problem areas. Such indisputable data reveals the reality of emission sources and helps authorities build local support for focused climate action. The International Atomic Energy Agency is working with a world meteorological organisation to help countries perform these measurements and generate the data needed. The IAEA and the WMO are setting up regional centres to analyse the data received and teach scientists how to apply this technique in their home countries. Because the air in each country will tell a different story and we can't solve a problem that we don't understand.