We can now tell how much CO2 in the air is due to fossil fuel burning

A way of directly measuring the carbon dioxide released by burning fossil fuels could help cities and countries monitor their efforts to reduce emissions in near real time. "We are in a shrinking window of time to do this, so I think we really need to know what the situation is as quickly and as accurately as possible," says Penelope Pickers at the University of East Anglia, UK. At present, governments and research organisations estimate countries' overall emissions based on data such as how much oil or gas has been sold. While initial estimates are often made fairly quickly, it can take years to fully compile this information and estimates can vary substantially. Measuring fossil fuel emissions directly would help confirm the accuracy of these inventory-based estimates and reveal more quickly if emission-reduction policies are working or not.