New Delhi, July 21 -- US President Donald Trump has spotlighted how unacceptable polluted air is. Yesterday, as Canadian wildfires affected New York, he held Canada responsible for the poor air quality under which the World Cup final was being played. His reaction to air pollution offers an opportunity to reflect on air quality for three reasons. First, Trump's anger about the situation is justified. By condemning the air quality, he reminds the world not to normalise it. Second, by blaming Canada, he raises a more complex issue: the commons belong to everyone. Canada cannot control climate change and the resulting forest fires, much less the direction of the wind. But what happens when one country suffers because of activities in another? Trump has even suggested that he could add it to the tariffs. Although I wonder whether he will follow through on that threat, my greater interest lies in the question of climate reparations. The developed world had committed to helping other countries combat climate change and compensate them for loss and damage. It has done very little so far. Can Trump's demand for compensation be leveraged by the world's most vulnerable countries? Finally, Trump's words, and their timing, underscore the need for clean air in sports and at sporting events. He reminds us that clean air ought to be a way of life. This should push the world to stop holding marathons, matches and other sporting events during periods of peak pollution. We often disagree with Trump. Here is one occasion when few can contest what he is saying. It may well be his global green leadership moment....