Efforts to reduce emissions 'need consistent counting'

The oil industry could find it hard to reduce emissions based on data from city authorities, due to the different accounting methods used.

According to Maike Sippel of the University of Stuttgart, there are a range of different tracking methods used when estimating the carbon output of different cities' populations.

For example, transport - one of the oil industry's major target markets and a significant source of carbon dioxide - can be counted in one of at least three ways.

One city might include all transport activity that occurs within its boundaries, while another might track its citizens' emissions, even when they are elsewhere in the world.

A third could omit transport from its carbon accounting entirely, making it harder to reduce emissions from vehicle use in any organised way.

The researcher says: "Almost half of all city targets may rather be symbolic, as cities do not publish emissions from the base year of their target."

Courses on offer at the University of Stuttgart are focused primarily on engineering and natural sciences, as well as social sciences and humanities.