Four world capitals are banning diesel vehicles from 2025

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The mayors of four major cities – Mexico City, Madrid, Paris and Athens – have pledged to ban diesel vehicles from their streets by 2025.

The mayors signed an "Air Quality Declaration" at the C40 Mayors Summit, which is being held in Mexico City. They also stated they would promote walking and cycling as well as encourage the use of alternative vehicles.

Air pollution is a major problem around the world, with the World Health Organization (WHO) stating that around 3 million deaths every year are linked to people's exposure to outdoor air pollution. In 2012 the International Agency for Research on Cancer – part of the WHO – classified diesel engine exhaust as "carcinogenic to humans."

"Mayors have already stood up to say that the climate change is one of the greatest challenges we face," Anne Hidalgo, the mayor of Paris, said in a news release.

"Today, we also stand up to say we no longer tolerate air pollution and the health problems and deaths it causes – particularly for our most vulnerable citizens," Hidalgo, who is also the new chair of the C40 Cities Climate Leadership Group, added.

"Big problems like air pollution require bold action, and we call on car and bus manufacturers to join us."

The mayor of Athens, Giorgos Kaminis, did not hold back in stating his ambition for the city. "Our goal is to ultimately remove all cars from the center of Athens in the years to come," he said.

In other environment news, on Thursday the chief executive of Royal Dutch Shell told Reuters that the company was planning to connect part of its executive bonuses to greenhouse gas emissions.

"We have linked executive remuneration in the past to energy intensity and next year we are going to make it even more specific to the CO2 footprint metrics associated with these energy efficiencies," Ben van Beurden told Reuters.